The anatomy of the vascular and lymphatic systems

Pharyngeal artery

The pharyngeal artery gives off three or four branches to supply the constrictor muscles of the pharynx and stylopharyngeus. A variable ramus supplies the palate and may replace the ascending palatine branch of the facial artery. The artery descends forwards between the superior border of the superior constrictor and levator veli palatini to the soft palate, and also supplies a branch to the palatine tonsil and the pharyngotympanic tube.

Inferior tympanic artery

The inferior tympanic artery is a small branch that traverses the temporal canaliculus with the tympanic branch of the glossopharyngeal nerve and supplies the medial wall of the tympanic cavity.

Meningeal arteries

The meningeal arteries are small vessels that supply the nerves that traverse the foramen lacerum, jugular foramen and hypoglossal canal, and the associated dura mater and adjoining bone. One branch, the posterior meningeal artery, reaches the cerebellar fossa via the jugular foramen and is usually regarded as the terminal branch of the ascending pharyngeal artery.

Infrahyoid artery

The infrahyoid artery is a small branch that runs along the lower border of the hyoid bone deep to thyrohyoid and anastomoses with its fellow of the opposite side to supply the infrahyoid strap muscles.

Superior laryngeal artery

The superior laryngeal artery accompanies the internal laryngeal nerve. Deep to thyrohyoid, it pierces the lower part of the thyrohyoid membrane to supply the tissues of the upper part of the larynx. It anastomoses with its fellow of the opposite side and with the inferior laryngeal branch of the inferior thyroid artery.

Sternocleidomastoid artery

The sternocleidomastoid artery descends laterally across the carotid sheath and supplies the middle region of sternocleidomastoid. Like the parent artery itself, it may arise directly from the external carotid artery.

Cricothyroid artery

The cricothyroid artery crosses high on the anterior cricothyroid ligament, anastomoses with its fellow of the opposite side and supplies cricothyroid.

Suprahyoid artery

The suprahyoid artery is a small branch that runs along the upper border of the hyoid bone to anastomose with the contralateral artery and supply adjacent structures.

Dorsal lingual arteries

There are usually two or three small dorsal lingual arteries. They arise medial to hyoglossus and ascend to the posterior part of the dorsum of the tongue. They supply its mucous membrane and the palatoglossal arch, tonsil, soft palate and epiglottis and anastomose with their contralateral fellows.

Sublingual artery

The sublingual artery arises at the anterior margin of hyoglossus. It passes forwards between genioglossus and mylohyoid to the sublingual gland, and supplies the gland, mylohyoid and the buccal and gingival mucous membranes. One branch pierces mylohyoid and joins the submental branches of the facial artery. Another branch courses through the mandibular gingivae to anastomose with its contralateral fellow. A single artery arises from this anastomosis and enters a small foramen (lingual foramen) on the mandible, situated in the midline on the posterior aspect of the symphysis immediately above the genial tubercles.

Deep lingual artery

The deep lingual artery is the terminal part of the lingual artery and is found on the inferior surface of the tongue near the lingual frenulum.

In addition to the lingual artery, the tonsillar and ascending palatine branches of the facial and ascending pharyngeal arteries also supply tissue in the root of the tongue. In the region of the valleculae, epiglottic branches of the superior laryngeal artery anastomose with the inferior dorsal branches of the lingual artery.

Ascending palatine artery

The ascending palatine artery arises close to the origin of the facial artery. It passes up between styloglossus and stylopharyngeus to reach the side of the pharynx, along which it ascends between the superior constrictor of the pharynx and medial pterygoid towards the cranial base. It bifurcates near levator veli palatini. One branch follows this muscle, winding over the upper border of the superior constrictor of the pharynx to supply the soft palate and to anastomose with its fellow of the opposite side and the greater palatine branch of the maxillary artery. The other branch pierces the superior constrictor muscle to supply the tonsil and pharyngotympanic tube, and to anastomose with the tonsillar and ascending pharyngeal arteries (see Fig. 40.7 ).

Tonsillar artery

The tonsillar artery provides the main blood supply to the palatine tonsil. It ascends between medial pterygoid and styloglossus, penetrates the superior constrictor of the pharynx at the upper border of styloglossus, and enters the inferior pole of the tonsil. Its branches ramify in the tonsil and in the musculature of the posterior part of the tongue. The tonsillar artery may sometimes arise from the ascending palatine artery.

Submental artery

The submental artery is the largest cervical branch of the facial artery (see Fig. 35.7A ). It arises as the facial artery separates from the submandibular gland and turns forwards on mylohyoid below the mandible. It supplies the overlying skin and muscles, and anastomoses with a sublingual branch of the lingual and mylohyoid branch of the inferior alveolar artery. At the chin, it ascends over the mandible and divides into superficial and deep branches that anastomose with the inferior labial and mental arteries to supply the chin and lower lip.

Glandular branches

Three or four large vessels supply the submandibular salivary gland and associated lymph nodes, adjacent muscles and skin.

Premasseteric artery

The premasseteric artery is small and inconstant. When present, it passes upwards along the anterior border of masseter and supplies the surrounding tissues.

Inferior labial artery

The inferior labial artery arises near the angle of the mouth, passes upwards and forwards under depressor anguli oris, and then penetrates orbicularis oris to run sinuously near the margin of the lower lip, between the muscle and the mucous membrane. It supplies the inferior labial glands, mucous membrane and muscles, and anastomoses with its contralateral fellow and with the mental branch of the inferior alveolar artery.

Superior labial artery

The superior labial artery is larger and more tortuous than the inferior labial artery. It pursues a similar course along the superior labial margin, between the mucous membrane and orbicularis oris, anastomoses with its contralateral fellow, and supplies the upper lip. It gives off an alar branch and a septal branch that ramifies anteroinferiorly in the nasal septum.

Lateral nasal artery

The lateral nasal artery is given off by the side of the nose, supplies the dorsum and ala of the nose, and anastomoses with its contralateral fellow. The lateral nasal artery can be replaced by a branch from the superior labial artery.

Transverse facial artery

The transverse facial artery arises before the superficial temporal artery emerges from the parotid gland. It traverses the gland, crosses masseter between the parotid duct and the zygomatic arch (accompanied by one or two facial nerve branches), and divides into numerous branches that supply the parotid gland and duct, masseter and adjacent skin. The branches anastomose with the facial, masseteric, buccal, lacrimal and infraorbital arteries, and can have a direct origin from the external carotid artery.

Auricular artery

The branches of the auricular artery are distributed to the lobule and lateral surface of the auricle and to the external acoustic meatus.

Zygomatico-orbital artery

The zygomatico-orbital artery may arise independently from the superficial temporal artery or from its middle temporal or parietal branches. It runs close to the upper border of the zygomatic arch, between the two layers of temporal fascia, to the lateral orbital angle. It supplies orbicularis oculi and anastomoses with the lacrimal and palpebral branches of the ophthalmic artery. A well-developed zygomatico-orbital artery can be associated with a delayed division of the superficial temporal artery into frontal and parietal branches.

Middle temporal artery

The middle temporal artery arises just above the zygomatic arch and perforates the temporal fascia to supply temporalis. It anastomoses with the deep temporal branches of the maxillary artery.

Frontal (anterior) branch

The frontal branch passes upwards towards the frontal tuberosity and supplies the muscles, skin and pericranium in this region. It anastomoses with its contralateral fellow and with the supraorbital and supratrochlear branches of the ophthalmic artery.

Parietal (posterior) branch

The parietal branch is larger than the frontal branch of the superficial temporal artery. It curves upwards and backwards, remains superficial to the temporal fascia, and anastomoses with its contralateral fellow and with the posterior auricular and occipital arteries.

Deep auricular artery

The deep auricular artery pierces the osseous or cartilaginous wall of the external acoustic meatus and supplies the skin of the external acoustic meatus and part of the tympanic membrane. A small branch contributes to the arterial supply of the temporomandibular joint.

Anterior tympanic artery

The anterior tympanic artery passes through the petrotympanic fissure to supply part of the lining of the middle ear and accompanies the chorda tympani nerve.

Middle meningeal artery

The middle meningeal artery is the main source of blood to the calvaria (see Fig. 38.22 ). It may arise either directly from the first part of the maxillary artery or from a common trunk with the inferior alveolar artery. When the maxillary artery lies superficial to lateral pterygoid, the middle meningeal artery is usually the first branch of the maxillary artery: this is not usually the case when the maxillary artery takes a deep course in relation to the muscle. The middle meningeal artery ascends between the sphenomandibular ligament and lateral pterygoid, passes between the two roots of the auriculotemporal nerve, and leaves the infratemporal fossa through the foramen spinosum to enter the cranial cavity medial to the midpoint of the zygomatic bone. It then runs in an anterolateral groove on the squamous part of the temporal bone, dividing into frontal and parietal branches (see Fig. 25.10A ). The larger frontal (anterior) branch crosses the greater wing of the sphenoid and enters a groove or canal in the sphenoidal angle of the parietal bone (the sphenoparietal canal). It divides into branches between the dura mater and cranium; some branches ascend to the vertex. The parietal (posterior) branch curves back on the squamous temporal bone, reaches the lower border of the parietal bone anterior to its mastoid angle and divides to supply the posterior parts of the dura mater and cranium. These frontal and parietal branches anastomose with their fellows and with the anterior and posterior meningeal arteries.

Ganglionic branches supply the trigeminal ganglion and associated roots. The petrosal branch enters the hiatus for the greater petrosal nerve, supplies the facial nerve, geniculate ganglion and tympanic cavity, and anastomoses with the stylomastoid artery ( ). The superior tympanic artery runs in the canal for tensor tympani and supplies the muscle and the mucosa that lines the canal. Temporal branches traverse minute foramina in the greater wing of the sphenoid and anastomose with deep temporal arteries that supply temporalis. An anastomotic branch enters the orbit laterally in the superior orbital fissure, and anastomoses with a recurrent branch of the lacrimal artery; enlargement of this anastomosis is believed to account for the occasional origin of the lacrimal artery from the middle meningeal artery.

Accessory meningeal artery

The accessory meningeal artery may arise from the maxillary artery or the middle meningeal artery. It enters the cranial cavity through the foramen ovale and supplies the trigeminal ganglion, dura mater and bone. Its main distribution is extracranial, principally to medial pterygoid, lateral pterygoid (upper head), tensor veli palatini, the greater wing and pterygoid processes of the sphenoid bone, the mandibular nerve and the otic ganglion. It is sometimes replaced by separate small arteries.

Inferior alveolar artery

The inferior alveolar (dental) artery descends in the infratemporal fossa posterior to the inferior alveolar nerve. Here, it lies between the ramus of the mandible laterally and the sphenomandibular ligament medially. Before entering the mandibular foramen it gives off a mylohyoid branch, which pierces the sphenomandibular ligament to descend with the mylohyoid nerve in its groove on the inner surface of the ramus of the mandible. The mylohyoid artery ramifies superficially on the muscle and anastomoses with the submental branch of the facial artery. The inferior alveolar artery then traverses the mandibular canal with the inferior alveolar nerve to supply the mandibular molars and premolars, and divides into the incisive and mental arteries near the first premolar.

The incisive artery continues below the incisor teeth (which it supplies) to the midline, where it anastomoses with its fellow, although few anastomotic vessels cross the midline. In the canal, the arteries supply the mandible, tooth sockets and teeth via branches that enter the minute hole at the apex of each root to supply the pulp. The mental artery emerges onto the face from the mandibular canal at the mental foramen, supplies muscles and skin in the chin region, and anastomoses with the inferior labial and submental arteries. Near its origin, the inferior alveolar artery has a lingual branch, which descends with the lingual nerve to supply the lingual mucous membrane. The pattern of branching of the inferior alveolar artery reflects that of the nerves of the same name.

Deep temporal arteries

The arterial supply to the temporalis in the coronal plane is concentrated mainly on its medial and lateral aspects. The anterior and posterior branches of the deep temporal arteries pass between temporalis and the pericranium, producing shallow grooves in the bone. They anastomose with the middle temporal branch of the superficial temporal artery situated laterally ( ). The anterior deep temporal artery anastomoses with the lacrimal artery by small branches that perforate the zygomatic bone and greater wing of the sphenoid.

Masseteric artery

The masseteric artery is small and accompanies the masseteric nerve as it passes through the mandibular incisure (notch), posterior to the tendon of temporalis, to enter the deep surface of masseter (see Fig. 38.20 ). Its branches can also supply the temporomandibular joint. The masseteric artery anastomoses with the masseteric branches of the facial artery and with the transverse facial branch of the superficial temporal artery. This vessel is at risk and may cause considerable bleeding if damaged when the sigmoid notch is entered or split surgically.

Pterygoid arteries

The pterygoid arteries are irregular in number and origin, and are distributed to lateral and medial pterygoid.

Buccal artery

The buccal artery emerges onto the face from the infratemporal fossa. It runs obliquely forwards between medial pterygoid and the attachment of temporalis, accompanying the lower part of the buccal branch of the mandibular nerve, to supply the skin and mucosa over buccinator (see Fig. 38.21A ). It anastomoses with branches of the facial and infraorbital arteries. A small lingual branch may be given off to accompany the lingual nerve and supply structures in the floor of the mouth.

Posterior superior alveolar artery

The posterior superior alveolar artery usually arises from the maxillary artery within the pterygopalatine fossa and runs through the pterygomaxillary fissure onto the maxillary tuberosity. It gives off branches that penetrate the bone here to supply the maxillary molar and premolar teeth and the maxillary air sinus, and other branches that supply the buccal mucosa. Occasionally the posterior superior alveolar artery arises from the infraorbital artery.

Infraorbital artery

The infraorbital artery often arises with the posterior superior alveolar artery. It enters the orbit posteriorly through the inferior orbital fissure. Accompanying the infraorbital nerve, it passes along the infraorbital groove of the maxilla in the floor of the orbit before entering the infraorbital canal, and emerges onto the face through the infraorbital foramen. On the face the infraorbital artery supplies the lower eyelid, the lateral aspect of the nose and the upper lip.

While in the infraorbital groove, it gives off branches that supply inferior rectus and inferior oblique, the nasolacrimal sac and, occasionally, the lacrimal gland.

Within the infraorbital canal it gives off the anterior superior alveolar artery which curves through the canalis sinuosus to supply the upper incisor and canine teeth and the mucous membrane in the anterior part of the maxillary sinus. The canalis sinuosus swerves laterally from the infraorbital canal and inferomedially below it in the wall of the maxillary sinus, following the rim of the anterior nasal aperture, between the alveoli of canine and incisor teeth and the nasal cavity. It ends near the nasal septum where its terminal branch emerges. The canal may be up to 55 mm long.

A middle superior alveolar artery is often described. When present, it branches from the infraorbital artery within the infraorbital canal and runs inferiorly along the lateral wall of the maxillary sinus towards the region of the canine and lateral incisor teeth, forming anastomotic arcades with the anterior and posterior superior alveolar arteries, and terminating near the canine tooth.

The infraorbital artery has extensive anastomoses with the transverse facial and buccal arteries and with branches of the ophthalmic and facial arteries.

Artery of the pterygoid canal

The artery of the pterygoid canal (Vidian artery) usually arises as a branch of the distal part of the maxillary artery or sometimes as a branch of the petrous segment of the internal carotid artery. It passes through the pterygoid canal and anastomoses with the pharyngeal, ethmoidal and sphenopalatine arteries in the pterygopalatine fossa and with the ascending pharyngeal, accessory meningeal, ascending palatine and descending palatine arteries in the oropharynx and around the pharyngotympanic tube. Through these complex anastomoses, the artery of the pterygoid canal contributes to the supply of part of the pharyngotympanic tube, the tympanic cavity and the upper part of the pharynx. It can also anastomose with the artery of the foramen rotundum and so communicate with branches of the cavernous portion of the internal carotid artery.

The communication between the internal and external carotid arteries via the artery of the pterygoid canal is one of a number of collateral vascular pathways that exist between the external carotid artery and branches of the petrous and intracavernous segments of the internal carotid artery. Albeit small and difficult to demonstrate angiographically, these vascular connections may nevertheless provide the arterial supply for arteriovenous malformations, dural-based fistulae and skull base tumours, and may also compensate for occlusion of the internal carotid artery. They also pose a risk of inadvertent embolization of the brain parenchyma during interventional angiography of the external carotid artery system.

There are extensive communications between the artery of the pterygoid canal and the highly vascular nasopharyngeal mucosa. Embolization of branches of the external carotid artery can result in incomplete obliteration of a vascular nasopharyngeal lesion when the artery of the pterygoid canal arises from the internal carotid artery. The collateral circulation provided by the artery of the pterygoid canal can help to maintain cerebral circulation if there is stenosis of the petrous internal carotid artery proximal to the point where the artery of the pterygoid canal joins it, because blood flow in the post-stenotic segment of the internal carotid artery will be supplemented from the external carotid artery via the artery of the pterygoid canal (see Fig. 38.29 ) ( , , ).

Pharyngeal artery

The pharyngeal branch of the maxillary artery passes through the palatovaginal canal, accompanying the nerve of the same name, and is distributed to the mucosa of the nasal roof, nasopharynx, sphenoidal air sinus and pharyngotympanic tube.

Greater (descending) palatine artery

The greater palatine artery leaves the pterygopalatine fossa through the greater (anterior) palatine canal, within which it gives off two or three lesser palatine arteries. The greater palatine artery supplies the inferior meatus of the nasal cavity, then passes onto the roof of the hard palate at the greater (anterior) palatine foramen and runs forwards to supply the hard palate and the palatal gingivae of the maxillary teeth. It gives off a branch that runs up into the incisive canal to anastomose with the nasopalatine artery and so contribute to the arterial supply of the nasal septum. The lesser palatine arteries emerge on to the palate through the lesser (posterior) palatine foramen, or foramina, and supply the soft palate.

As the greater palatine artery runs the length of the hard palate, it permits axial mucoperiosteal flaps to be raised, if necessary bilaterally, for the reconstruction of local defects. It is also possible to pedicle the entire mucoperiosteum of the hard palate on a single greater palatine artery. The vascular supply to the denuded palatal bone is sufficient, presumably from its nasal surface, to permit regeneration of the palatal soft tissue. Contracture of the regenerated tissue does not occur because the defect lies over the palatal bone ( , , ).

Sphenopalatine artery

The sphenopalatine artery and the greater palatine artery are the terminal branches of the maxillary artery. The sphenopalatine artery is the principal artery that supplies the mucosa of the nasal cavity. It passes through the sphenopalatine foramen posterior to the superior meatus. From here, its posterior lateral nasal branches ramify over the turbinates and meatuses and anastomose with the ethmoidal arteries and nasal branches of the greater palatine artery to supply the frontal, maxillary, ethmoidal and sphenoidal air sinuses. The sphenopalatine artery next crosses anteriorly on the inferior surface of the sphenoid and ends on the nasal septum in a series of posterior septal branches that anastomose with the ethmoidal arteries (see Fig. 39.9 ).

Ligation of the sphenopalatine artery may be necessary in the control of refractory epistaxis. It is usually located endoscopically at the postero-inferior end of the middle turbinate. Multiple branches may be encountered. The sphenopalatine artery provides the axial blood supply to the nasal septal mucosal flap (nasoseptal flap) used in endoscopic skull-base repair, a reflection of its contribution to the vascular supply to the nasal cavity ( ).

Cervical part

The cervical part begins at the carotid bifurcation and ascends anterior to the transverse processes of the upper three cervical vertebrae and enters the cranial cavity via the carotid canal in the petrous part of the temporal bone. The artery has no branches in the neck and so is easily distinguishable from the external carotid artery, should the latter require ligation, e.g. to control haemorrhage from a penetrating injury to the neck ( ).

Petrous part

The petrous part of the internal carotid artery ascends in the carotid canal, curves anteromedially and then superomedially above the cartilage that fills the foramen lacerum, and enters the cranial cavity. It lies at first anterior to the cochlea and tympanic cavity, and is separated from the latter and the pharyngotympanic tube by a thin, bony lamella that is cribriform in the young and partly absorbed in old age. Further anteriorly, it is separated from the trigeminal ganglion by the thin roof of the carotid canal, although this is often deficient. The artery is surrounded by a venous plexus and by the carotid autonomic plexus, derived from the internal carotid branch of the superior cervical ganglion. The petrous part of the artery gives rise to two branches. The caroticotympanic artery is a small, occasionally double, vessel that enters the tympanic cavity by a foramen in the carotid canal and anastomoses with the anterior tympanic branch of the maxillary artery and the stylomastoid artery. The pterygoid artery is inconsistent; when present, it enters the pterygoid canal with the nerve of the same name, and anastomoses with a (recurrent) branch of the greater palatine artery.

Cavernous part

The cavernous part of the internal carotid artery ascends to the posterior clinoid process. It turns anteriorly to the side of the body of the sphenoid within the cavernous sinus and then curves superiorly and medial to the anterior clinoid process, to emerge through the dural roof of the sinus. The oculomotor, trochlear, ophthalmic and abducens nerves are lateral to it within the cavernous sinus. The abducens nerve is closely related to the lateral wall of the internal carotid artery, whilst the oculomotor and trochlear nerves are situated in the lateral wall of the cavernous sinus (see Figure 25.8, Figure 25.9 ). This explains the higher risk of abducens nerve injury secondary to pathology such as aneurysms of the cavernous part of the carotid artery. Occasionally the caroticoclinoid ligament between the anterior and middle clinoid processes becomes ossified, forming a bony ring (caroticoclinoid foramen) around the artery ( ).

The cavernous part of the artery gives off a number of small vessels. Branches supply the trigeminal ganglion, the walls of the cavernous and inferior petrosal sinuses, and the nerves contained therein. A minute meningeal branch passes over the lesser wing of the sphenoid to supply the dura mater and bone in the anterior cranial fossa, and also anastomoses with a meningeal branch of the posterior ethmoidal artery. Numerous small hypophysial branches supply the neurohypophysis, and are of particular importance because they form the pituitary portal system (see Fig. 23.11 ).

Intracranial part

After piercing the dura mater, the internal carotid artery turns back below the optic nerve to run between it and the oculomotor nerve. It reaches the anterior perforated substance at the medial end of the lateral fissure and terminates by dividing into the anterior and middle cerebral arteries (see Fig. 26.3 ).

Several preterminal vessels leave the cerebral portion of the internal carotid. The ophthalmic artery arises from the anterior part of the internal carotid as it leaves the cavernous sinus, often at the point of piercing the dura, and enters the orbit through the optic canal. The posterior communicating artery (see Fig. 26.3 ) runs back from the internal carotid above the oculomotor nerve, and anastomoses with the posterior cerebral artery (a terminal branch of the basilar artery), thereby contributing to the circulus arteriosus around the interpeduncular fossa. The posterior communicating artery is usually very small. However, sometimes it is so large that the posterior cerebral artery is supplied via the posterior communicating artery rather than from the basilar artery (‘fetal posterior communicating artery’); it is often larger on one side only. Small branches from its posterior half pierce the posterior perforated substance together with branches from the posterior cerebral artery. Collectively they supply the medial thalamic surface and the walls of the third ventricle. The anterior choroidal artery leaves the internal carotid just distal to its posterior communicating branch and passes back above the medial part of the uncus. It crosses the optic tract to reach and supply the crus cerebri of the midbrain, then turns laterally, recrosses the optic tract, and gains the lateral side of the lateral geniculate body, which it supplies with several branches. It finally enters the inferior horn of the lateral ventricle via the choroidal fissure and ends in the choroid plexus. This small, but important, vessel also contributes to the blood supply of the globus pallidus, caudate nucleus, amygdala, hypothalamus, tuber cinereum, red nucleus, substantia nigra, posterior limb of the internal capsule, optic radiation, optic tract, hippocampus and the fimbria of the fornix.

The combination of the petrous, cavernous and intracranial parts of the internal carotid artery is called the ‘carotid siphon’ because of its sigmoid course (see Fig. 26.1 and Video 26.1 ). However, in infants, the parasellar region of the internal carotid artery does not form a siphon but takes a relatively straight course ( ). The cranial and sympathetic nerves therefore have different topographical relationships with the artery in the infant compared with that found in older children and adults.

The initial millimetres of the intracranial part lie between two rings (proximal and distal rings) of dense connective tissue that surround the carotid artery where the ophthalmic artery usually branches. In cases of surgical clipping of ophthalmic artery aneurysms, it is of surgical relevance for neurosurgeons to expose this part of the artery by removing the anterior clinoid process and exposing this segment of the internal carotid artery (see Video 26.1 ).

Central or perforating arteries

Numerous small central (perforating or ganglionic) arteries arise from the circulus arteriosus or from vessels near it (see Fig. 26.3 ). Many of these enter the brain through the anterior and posterior perforated substances. Central branches supply nearby structures on or near the base of the brain together with the interior of the cerebral hemisphere, including the internal capsule, basal ganglia and thalamus. These branches form four principal groups. The anteromedial group arises from the anterior cerebral and anterior communicating arteries, and passes through the medial part of the anterior perforated substance. These arteries supply the optic chiasma, lamina terminalis, anterior, preoptic and supraoptic areas of the hypothalamus, septum, para-olfactory areas, anterior columns of the fornix, cingulate gyrus, rostrum of the corpus callosum and the anterior part of the putamen and the head of the caudate nucleus. The posteromedial group comes from the entire length of the posterior communicating artery and from the proximal portion of the posterior cerebral artery. Anteriorly, these arteries supply the hypothalamus and pituitary gland, and the anterior and medial parts of the thalamus via thalamo-perforating arteries. Caudally, branches of the posteromedial group supply the mammillary bodies, subthalamus, the lateral wall of the third ventricle, including the medial thalamus, and the globus pallidus. The anterolateral group is mostly comprised of branches from the proximal part of the middle cerebral artery that are also known as striate, lateral striate or lenticulostriate arteries. They enter the brain through the anterior perforated substance and supply the posterior striatum, lateral globus pallidus and the anterior limb, genu and posterior limb of the internal capsule. The medial striate artery, derived from the middle or anterior cerebral arteries, supplies the rostral part of the caudate nucleus and putamen, and the anterior limb and genu of the internal capsule. The posterolateral group is derived from the posterior cerebral artery distal to its junction with the posterior communicating artery, and supplies the cerebral peduncle, colliculi, pineal gland and, via thalamogeniculate branches, the posterior thalamus and medial geniculate body.

Right coronary artery

The right coronary artery arises from the right aortic sinus; its opening is usually below the sinutubular junction (see Fig. 57.23 ). The artery is usually single, although up to four openings have been observed, reflecting the independent origins of the conal, sinuatrial nodal and ventricular arteries (see Figure 57.42, Figure 57.43 ). The right coronary artery passes at first anteriorly and slightly to the right between the right atrial auricle and pulmonary trunk. On reaching the atrioventricular sulcus, it descends almost vertically to the right side of the inferior cardiac border, curving around it into the inferior part of the sulcus in which it passes towards the cardiac crux (the junction of the atrioventricular, interatrial and interventricular sulci) (see Fig. 57.4B ). The artery ends a little to the left of the crux, often by anastomosing with the circumflex branch of the left coronary artery. The right coronary artery may end near the right cardiac border, between this and the crux, or more often it reaches the left border, replacing the more distal part of the circumflex artery. Its branches supply the right and variable parts of the left chambers and atrioventricular septum. Usually, the first branch is the conal branch of the right coronary artery ( ). This vessel arises independently from the right aortic sinus in approximately 33% of hearts and is sometimes termed the third coronary artery, but this is an inappropriate term because a similarly named vessel arises from the left coronary circulation. The conal branch of the right coronary artery branches anteroinferiorly over the conus arteriosus (infundibulum) and over the superior aspect of the right ventricle, sometimes anastomosing with a similar branch from the anterior interventricular (left anterior descending) artery to form Vieussens arterial ring, an inconstant anastomosis around the right ventricular outflow tract that may provide an important collateral circulation in cases of arterial occlusion (see Figure 57.44, Figure 57.45 ) ( ).

The first segment of the right coronary artery (between its origin and the right side of the inferior cardiac margin) gives off anterior atrial and ventricular branches that diverge widely. The ventricular arteries arise at almost 90° from the right coronary artery, an arrangement that is in marked contrast to the more acutely angled origins of the ventricular branches of the left coronary artery. The anterior ventricular branches, usually two or three, ramify towards the cardiac apex, but they rarely reach the apex unless the right marginal artery is included within this group. The right marginal artery is greater in calibre than the other anterior ventricular arteries and reaches the cardiac apex in most hearts. When it is very large, there may be no additional anterior ventricular branch. Two, sometimes three, small inferior ventricular branches, arise from the second segment of the right coronary artery between the right side of the inferior cardiac margin and cardiac crux to supply the inferior aspect of the right ventricle. Their size is inversely proportional to that of the right marginal artery, which usually extends to the inferior cardiac surface. On approaching the cardiac crux, the right coronary artery normally produces up to three inferior interventricular branches (occasionally none). The actual inferior interventricular artery sits within the interventricular sulcus, and may be flanked either to the right or left, or on both sides, by these parallel branches. When these flanking vessels exist, branches of the inferior interventricular artery are small and sparse. The inferior interventricular artery is occasionally replaced by a branch of the left coronary artery. Although the atrial branches of the right coronary artery are sometimes described as part of anterior, lateral (right or marginal) and posterior groups, they are usually small single vessels, 1 mm in diameter (see Figure 57.46, Figure 57.47, Figure 57.48 ). The right anterior and lateral branches (occasionally double, and very rarely triple) mainly supply the right atrium. The posterior branch is usually single and supplies both atria.

The artery of the sinuatrial node is an atrial branch of variable origin, distributed largely to right atrial myocardium. Its origin is variable: most commonly, it arises as the first atrial branch of the right coronary artery, less often from its right lateral atrial branch, and least often from its inferior atrioventricular part. It may sometimes originate from the circumflex branch of the left coronary artery. It usually passes posteriorly in the groove between the right atrial auricle and ascending aorta, and branches around the junction of the superior vena cava and right atrium, typically as an arterial loop from which small branches supply the right atrium. A large branch, the ramus cristae terminalis, traverses and supplies the sinuatrial node: it would seem more appropriate to name this branch the nodal artery, given that the vessel currently bearing this name is predominantly atrial in distribution.

Septal perforating branches of the right coronary artery are relatively short and leave the inferior interventricular branch to supply the inferior part (about one-third) of the interventricular septum. They are numerous but do not usually reach the apical region of the septum. The largest inferior septal perforating artery, usually the first branch, commonly arises from the inverted loop said to characterize the right coronary artery at the crux and it almost always supplies the atrioventricular node. Small, recurrent atrioventricular branches originate from the ventricular branches of the right coronary artery as they cross the atrioventricular sulcus and supply adjacent atrial myocardium.

Left coronary artery

The left coronary artery is usually larger in calibre than the right. It supplies a greater volume of myocardium, including almost all of the left ventricle and atrium, and most of the interventricular septum (see Figure 57.42, Figure 57.49, Figure 57.50, Figure 57.51 ). In hearts with right dominance, the right coronary artery supplies a variable amount of the inferior region of the left ventricle (see Fig. 57.41A–C ).

The left coronary artery arises from the left aortic sinus. The opening of the artery sometimes lies inferior to the margin of the valve leaflets and may be double, usually leading into the circumflex and anterior interventricular (left anterior descending) branches of the left coronary artery. Its initial portion, between its opening and first branches, varies in length from a few millimetres to a few centimetres. The artery lies between the pulmonary trunk and the left atrial auricle, emerging into the atrioventricular sulcus, where it turns left. This part is loosely embedded in subepicardial fat and usually has no branches, but may give off a small atrial branch and, rarely, the sinuatrial nodal artery. Reaching the atrioventricular sulcus, the left coronary artery divides into its two main branches: the circumflex and anterior interventricular arteries.

The anterior interventricular artery is commonly described as the continuation of the left coronary artery. It descends obliquely forwards and to the left in the interventricular sulcus (see Fig. 57.52 ), sometimes deeply embedded in or crossed by myocardial tissue (myocardial bridges), and by the great cardiac vein and its tributaries.

Myocardial bridges are reported to have a frequency varying from 0.5 to 40% when identified clinically and from 15 to 85% when found at autopsy (see Fig. 57.53 ). The wide variation in frequency indicates that many bridges may be asymptomatic during life. The major clinical conditions produced by a myocardial bridge are cardiac ischaemia, atherosclerosis and sudden cardiac death. The incidence of atherosclerosis is increased when the right coronary artery is bridged. Although a relationship between myocardial bridges and sudden cardiac death has not been established, autopsy series have shown histological evidence of otherwise unexplained ischaemia in individuals with myocardial bridges; many died during exercise and had no other risk factors for coronary arterial disease.

Almost invariably, the anterior interventricular artery reaches the cardiac apex, where it terminates in around 33% of hearts. More frequently, it curves around the notch of the cardiac apex into the inferior interventricular sulcus and passes one-third to one-half of the way along its length, meeting the terminal parts of the inferior interventricular branches of the right coronary artery.

The anterior interventricular artery gives off right and left anterior ventricular and anterior septal branches, and a variable number of corresponding posterior branches. Anterior right ventricular branches are small and rarely number more than one or two; the right ventricle is supplied almost entirely by the right coronary artery. Up to nine large left anterior ventricular arteries branch at acute angles from the anterior interventricular artery, crossing the anterior aspect of the left ventricle diagonally, with the largest reaching the rounded left (obtuse) cardiac border. One, termed the left diagonal artery, often dominates, sometimes arising separately from the left coronary artery, which then ends by trifurcation. It is reported in at least 33–50% of hearts, and may be doubled in around 20%. A small left conal artery frequently leaves the anterior interventricular artery near its origin, and anastomoses on the conus arteriosus with its counterpart from the right coronary artery and with the vasa vasorum of the pulmonary trunk and aorta. The anterior septal perforating branches leave the anterior interventricular artery almost perpendicularly, and pass posteroinferiorly within the septum, usually supplying its anterior two-thirds. The first septal perforator artery usually supplies the atrioventricular bundle at the point of its division. Small inferior septal branches from the same source supply the inferior third of the septum for a variable distance from the cardiac apex ( ).

The circumflex branch of the left coronary artery, comparable to the anterior interventricular artery in calibre, curves leftwards in the atrioventricular sulcus, and continues around the left cardiac border into the posterior and then inferior part of the sulcus, terminating to the left of the cardiac crux in most hearts, although sometimes continuing as the inferior interventricular artery. Proximally, the left atrial auricle usually overlaps it. A large ventricular branch, the left marginal artery, normally arises from the left circumflex artery at a 90° angle and branches over the rounded left border, supplying much of the adjacent left ventricle, typically to its apex. Smaller anterior and inferior branches of the circumflex artery also supply the left ventricle. Anterior ventricular branches (from one to five, commonly two or three) course parallel to the diagonal artery when it is present, and replace it when it is absent. Inferior ventricular branches are smaller and fewer because the left ventricle is partly supplied by the inferior interventricular artery. When this artery is small or absent, it is accompanied or replaced by often doubled or tripled interventricular continuations of the circumflex artery.

The artery to the sinuatrial node is often derived from the first 1–2 cm of the circumflex artery after its origin from the left coronary artery (anterior circumflex segment) and less often from the remaining length of the circumflex artery. It passes over and supplies the left atrium, encircles the superior vena cava (similar to a right coronary sinuatrial nodal branch) and sends a large branch through the node; despite its name, it is predominantly atrial in distribution. The artery to the atrioventricular node, sometimes the terminal branch of the circumflex artery (20%), arises near the cardiac crux. When this occurs, the circumflex artery usually gives off the inferior interventricular artery, an example of left dominance.

Pneumomediastinum and aortic nipple

Pneumomediastinum is an overarching term that describes the presence of air in the mediastinum. It may arise from a wide range of pathological conditions or physiological states, e.g. penetrating trauma, ruptured major airways or oesophagus, hyperventilation or distressed ventilation such as acute asthma, periparturition or diabetic ketoacidosis.

The aortic nipple is the radiographic term used to describe a lateral nipple-like projection located on the aortic knuckle. It corresponds to the end-on appearance of the left superior intercostal vein coursing anteriorly and is not observed in all individuals. It may be mistaken radiologically for lymphadenopathy or an intrapulmonary nodule or neoplasm. Despite their relative independence, the aortic nipple is defined by new contours in cases of pneumomediastinum, taking on an ‘inverted aortic nipple’ appearance (see Fig. 58.5 ). In this position, the inverted aortic nipple may facilitate radiographic discrimination of pneumomediastinum from similar conditions. The presence of an aortic nipple has also been shown to precede pathological conditions such as venous obstruction in the superior and inferior vena cavae or left brachiocephalic vein, and has been identified in conditions where venous flow through the left superior intercostal vein is increased (e.g. portal venous hypertension and certain congenital venous anomalies).

Coarctation of the thoracic aorta

The aortic lumen is occasionally partly or completely obliterated, either above (preductal or infantile type), opposite or just beyond (postductal or adult type), the entry of the ductus arteriosus. In the preductal type, the length of coarctation is variable, aortic arch hypoplasia is common, and the left subclavian and even the brachiocephalic trunk may be involved. Severe forms of infantile coarctation and its extreme form (aortic interruption) may be patent ductus arteriosus-dependent, as there is no time for effective collateral circulation to develop. Prostaglandin infusion prior to transfer, and surgery at a tertiary centre, often provide a good mid- to long-term outlook for such infants.

The postductal type of coarctation has been attributed to abnormal extension of tissue of the ductus arteriosus into the aortic wall, stenosing both vessels as the duct contracts after birth. This form may permit years of normal life, allowing the development of an extensive collateral circulation to the aorta distal to the stenosis (see Figure 58.7, Figure 58.8 ). High vascularity of the thoracic wall is important and clinically characteristic. Many arteries that arise indirectly from the aorta proximal to the region of coarctation anastomose with vessels that are connected to the aorta distal to the region of coarctation; these vessels form a bypass route and become greatly enlarged. Thus, in the thoracic wall, the thoraco-acromial, lateral thoracic and subscapular arteries (from the axillary artery), the suprascapular artery (from the subclavian artery) and the supreme intercostal artery (from the costocervical trunk) anastomose with other posterior intercostal arteries and the internal thoracic artery and its terminal branches (e.g. the musculophrenic artery) anastomose with many of the posterior intercostal arteries and the inferior epigastric arteries (from the external iliac artery). Posterior intercostal arteries are always involved, and enlargement of their dorsal branches may eventually groove (notch) the inferior margins of the ribs. The radiographic shadow of an enlarged left subclavian artery is also increased. Enlargement of the scapular vessels and anastomoses may lead to widespread interscapular pulsation which is palpated easily with the palm of the hand, and is sometimes heard on auscultation.

Aortic aneurysm formation

Degeneration of the aortic tunica media and intimal dissection play a major role in the pathogenesis of aneurysms affecting the ascending aorta and aortic arch. Smooth muscle cells are lost and elastic fibres degenerate, producing cystic spaces in the media that then fill with mucoid material. The loss of these structural cells leads to weakening of the wall with progressive dilation. Ageing and hypertension are major predisposing factors to cystic medial degeneration and there is a strong link with cigarette smoking. Thoracic aortic aneurysms are categorized by their location. A particular pattern of aortic root involvement, anulo-aortic ectasia, is seen in Marfan syndrome ( ). Descending aortic aneurysms are generally caused by atherosclerosis (90%) and the remainder result from mycotic disease or trauma.

Associations also exist between thoracic aortic aneurysm and other connective tissue diseases such as homocysteinuria and Ehlers–Danlos syndrome. A genetic relation is seen in familial thoracic aortic aneurysm syndrome ( ). Rarely, aneurysms may occur as a result of Takayasu’s arteritis, or infections within the aortic wall. Some aortic aneurysms are incidental findings on chest films or CT studies. Symptomatic cases present with breathlessness, unbearable chest and back pain, hoarse voice, cough and haemoptysis. Early diastolic murmurs caused by aortic regurgitation may be audible. Repair is carried out in patients with symptoms or fusiform dilation measuring more than 5 cm in diameter. Aneurysms may also occur in an aberrant right subclavian artery and may involve the diverticulum of Kommerell, leading to dysphagia and even tracheal compression. Inadvertent rupture may occur during endoscopy because of the retro-oesophageal location.

Aortic dissection

Aortic dissection occurs as a result of degeneration of the tunica media of the aortic wall and is associated with senescence, persistent hypertension or collagen vascular diseases such as Marfan syndrome. Many patients with aortic dissection have a pre-existing aneurysm. Other associations include aortic coarctation, Turner’s syndrome, cocaine abuse (<1%) and trauma during surgical procedures. There is a higher prevalence in males than females, but after 75 years of age there is no sex difference in prevalence ( ). In a classic aortic dissection, an intimal tear may occur, producing a split into the tunica media that creates a false lumen (see Fig. 58.9 ). If another tear occurs, connection can be made once again with the true lumen (double-barrel aorta). Additional aetiopathologies include penetrating atherosclerotic ulceration, where an atherosclerotic plaque ruptures into the aortic tunica media, and aortic intramural haematoma, where the vasa vasorum haemorrhage into the wall of the aorta ( ).

Aortic dissections are classified as types I, II, IIIa and IIIb (DeBakey classification), or types A and B (Stanford classification). Dissections that include the aorta proximal to the left subclavian artery, with or without distal extension, are classified as type I, II or A. Type I involves up to the entire aorta (ascending, arch and descending), whereas type II involves the ascending aorta only. Dissections that are distal to the left subclavian artery are classified as type IIIa (extend to the respiratory diaphragm), IIIb (extend below the respiratory diaphragm) or B. These cases present acutely with severe retrosternal, neck or interscapular chest pain. Depending on the extent of the dissection, they may be associated with neurological signs, diarrhoea or leg weakness. Extension into the pericardium causes cardiac tamponade and circulatory collapse. Diagnosis is established by echocardiography and on contrast-enhanced CT or magnetic resonance imaging (MRI). Medical management is possible for descending aortic dissections, while surgical repair is essential for ascending aortic or aortic arch dissection.

Pericardial branches

A variable number of small vessels are distributed to the posterior aspect of the pericardium.

Bronchial arteries

Bronchial arteries vary in number, size and origin. There is usually only one right bronchial artery that arises from either the right third posterior intercostal artery, or the superior left bronchial artery, or various right posterior intercostal arteries, and runs posteriorly on the right principal main bronchus. The left bronchial arteries, usually two, arise from the thoracic aorta, the superior near the fifth thoracic vertebra, the inferior below the left principal main bronchus, and run posterior to the left main bronchus. The bronchial arteries supply the pulmonary areolar tissue, bronchopulmonary lymph nodes, pericardium and oesophagus.

Oesophageal branches

Two or three bronchial arteries supply the thoracic oesophagus. Two or three oesophageal arteries that arise either anteriorly or from the right side of the descending thoracic aorta supply the distal oesophagus ( ).

Mediastinal branches

Numerous small vessels supply lymph nodes and areolar tissue in the posterior mediastinum.

Superior phrenic branches

Superior phrenic arteries arise from the distal descending thoracic aorta and are distributed posteriorly to the superior (thoracic) surface of the respiratory diaphragm, anastomosing with the musculophrenic and pericardiacophrenic arteries (see Fig. 55.6 ).

Posterior intercostal arteries

There are usually nine pairs of posterior intercostal arteries. They arise from the posterior aspect of the descending thoracic aorta and are distributed to the lower nine intercostal spaces (third to eleventh spaces). The right posterior intercostal arteries are longer because the aorta deviates to the left (see Fig. 53.18 ): they cross the vertebral bodies posterior to the oesophagus, thoracic duct and azygos vein, and the parietal pleura covering the right lung. The left posterior intercostal arteries travel posteriorly across the vertebral bodies and are in contact with the parietal pleura covering the left lung; the first and second are crossed by the left superior intercostal vein, and those located inferiorly are crossed by the hemiazygos and accessory hemiazygos veins. The sympathetic trunk and ganglia lie anterior to all of the arteries, and the thoracic splanchnic nerves are anterior to the more inferiorly located arteries.

Each artery crosses its intercostal space obliquely towards the angle of the rib above and continues forwards in its costal groove. It runs between the costal parietal pleura and associated endothoracic fascia, and the internal intercostal membrane as far as the angle of the rib, then passes between the internal and innermost intercostal muscles (see Fig. 53.17 ) and anastomoses with an anterior intercostal branch from either the internal thoracic or musculophrenic artery. Each artery is accompanied by a vein above and a nerve below, except in the upper spaces, where the nerve is initially superior to the artery. The third posterior intercostal artery anastomoses with the supreme intercostal artery and may provide the major supply to the second intercostal space. The inferior two posterior intercostal arteries continue anteriorly into the abdominal wall, where they anastomose with the subcostal, superior epigastric and lumbar arteries (see Fig. 52.3 ). Each posterior intercostal artery has dorsal, collateral, muscular and cutaneous branches (see Fig. 53.18 ).

Subcostal arteries

The subcostal arteries are the last paired branches of the descending thoracic aorta, in series with the posterior intercostal arteries and inferior to the twelfth ribs. Each runs laterally anterior to the body of the twelfth thoracic vertebra and posterior to the thoracic splanchnic nerves, sympathetic trunk, costal part of the parietal pleura and lumbar part of the respiratory diaphragm. The right subcostal artery is also posterior to the thoracic duct and azygos vein, while the left is posterior to the hemiazygos vein. Each artery enters the abdomen at the lower border of the twelfth rib, accompanied by the twelfth thoracic (subcostal) nerve, lying posterior to the lateral arcuate ligament and kidney, and anterior to quadratus lumborum. The right artery courses posterior to the ascending colon, and the left courses posterior to the descending colon. The subcostal arteries pierce the aponeurosis of transversus abdominis to become more superficial, and continue toward the anterior midline in the plane between transversus abdominis and internal abdominal oblique; they anastomose with the superior epigastric, lower posterior intercostal and lumbar arteries. Each has a dorsal branch, distributed like those of the posterior intercostal arteries.

Aberrant artery (right dorsal aorta vestige)

A small artery sometimes leaves the descending thoracic aorta from its right side near the origin of the right bronchial artery. It ascends to the right behind the trachea and oesophagus and may anastomose with the right supreme intercostal artery.

Aortic rupture in trauma

Rupture of the ascending aorta is usually associated with a high immediate mortality ( ). Blunt aortic rupture commonly occurs in road traffic accidents and has a 20% survival rate. There is usually a transverse tear involving the tunica intima and tunica media of the aortic wall; systemic circulatory pressure may cause the formation of a false aneurysm. Rupture of the isthmus region of the descending thoracic aorta is more common, probably because it marks the junction between the mobile and fixed parts of the aorta. Other sites include the ascending aorta proximal to the origin of the brachiocephalic trunk, the aortic arch and the abdominal aorta. Rupture is likely to be the result of a number of factors, including torsion, shear and stretching forces, possibly compounded by hydrostatic pressure.

Aortic atherosclerosis or calcification

Echocardiography, particularly transoesophageal, allows detailed assessment of proximal aortic atherosclerosis implicated in systemic embolic events and strokes, and the extent of turbulent flow. MRI can allow accurate assessment of the composition and size of atherosclerotic plaques and flow dynamics, permitting assessment of the risk of plaque rupture and thrombus formation.

Left gastric artery

The left gastric artery is the smallest branch of the coeliac trunk. It ascends to the left of the midline and crosses over the distal end of the left crus of the respiratory diaphragm beneath a fold of peritoneum in the upper posterior wall of the omental bursa (the gastropancreatic fold). Here, it lies adjacent to the left inferior phrenic artery and medial or anterior to the left suprarenal gland. It runs forwards into the superior portion of the lesser omentum adjacent to the proximal end of the lesser curvature, and then it turns anteroinferiorly to run along the lesser curvature between the two peritoneal leaves of the lesser omentum. At the highest point of its course it gives off one or more oesophageal branches. In its course along the lesser curvature it gives off multiple branches that run on to the anterior and posterior surfaces of the stomach, after which it anastomoses with the right gastric artery in the region of the angular incisure.

Rarely the left gastric artery (replaced or accessory) arises from the common hepatic or left hepatic arteries, or directly from the abdominal aorta ( ). The most common of these variations is an origin from the left hepatic artery, when the left gastric artery passes between the peritoneal layers of the proximal lesser omentum to reach the lesser curvature of the stomach. However, a replaced/accessory left hepatic artery arising from the left gastric artery is more common than a replaced/accessory left gastric artery origin.

Hepatic artery

During fetal and early postnatal life the common hepatic artery is the largest branch of the coeliac trunk, whereas in adults it is intermediate in size between the left gastric and splenic arteries. The common hepatic artery gives off the right gastric and gastroduodenal arteries (see Fig. 66.9A ). After originating from the coeliac trunk, it passes anteriorly and laterally, above the superior border of the pancreas, to the superior aspect of the first part of the duodenum. It is subdivided into the common hepatic artery, from the coeliac trunk to the origin of the gastroduodenal artery, and the proper hepatic artery, from that point to its bifurcation. Both parts ascend anterior to the hepatic portal vein and medial to the bile duct within the free margin of the hepatoduodenal ligament in the anterior wall of the omental foramen. The left and right hepatic arteries arise at a variable level below the porta hepatis. The right hepatic artery typically crosses posterior (occasionally anterior) to the common hepatic duct (see Fig. 66.9B ). Its usual course is toward the common hepatic duct: it bends inferiorly before crossing posterior to the duct and then bends back up toward the right hepatic duct lateral to the common hepatic duct and hepatic portal vein. Its close proximity to the bifurcation of the bile duct means that it is often involved or encased by bile duct cancers that arise at the bifurcation (hilar cholangiocarcinoma): the right hepatic artery is more frequently involved than the left hepatic artery in bile duct cancers of the porta hepatis. Occasionally the right hepatic artery crosses anterior to the common hepatic duct and is more vulnerable to injury during biliary surgery. It almost always divides into an anterior branch supplying segments V and VIII and a posterior branch supplying segments VI and VII. The anterior division also often supplies a branch to segment I and the gallbladder. The proper hepatic artery sometimes divides at a more inferior level close to its origin, and occasionally it divides at a superior level, well to the left of the porta hepatis. The main significance of an early division is that the right hepatic artery can pass posterior to the hepatic portal vein ( ). The segmental arteries of the liver are macroscopically end arteries, although some collateral circulation occurs between segments via fine terminal branches.

Anatomical variants of the normal arrangement of the hepatic arteries are found in about one-third of individuals and are important to recognize because they are relevant to surgical and interventional radiological procedures ( , , , ). An artery that supplies a part of the liver in addition to the normal artery supplying that part is defined as an accessory artery. A replaced hepatic artery is an artery that does not originate from an orthodox position and provides the sole supply to that part of the liver.

A replaced proper hepatic artery can arise from the superior mesenteric artery (see Fig. 66.10 ) and can be suspected at surgery by a relatively superficial hepatic portal vein (reflecting the absence of a hepatic artery that would normally ascend in front of the vein). More commonly, a replaced or accessory right hepatic artery arises from the superior mesenteric artery (see Figure 66.10, Figure 66.11 ). In such cases, the variant artery runs in the lesser omentum posterior to the hepatic portal vein and bile duct and can usually be identified at surgery by palpable pulsation posterior to the hepatic portal vein. An accessory right hepatic artery can be injured during resection of the pancreatic head because it lies close to the hepatic portal vein. Occasionally a replaced or accessory left hepatic artery arises from the left gastric artery, entering the liver through the umbilical fissure; this artery provides a source of collateral supply in cases where the arteries at the porta hepatis are occluded, but it can also be injured during mobilization of the stomach as it lies in the superior portion of the lesser omentum. Rarely an accessory left or right hepatic artery arises from the gastroduodenal artery or directly from the aorta. The presence of replaced arteries can be life-saving in patients with bile duct cancer; because they are further away from the bile duct they tend to be spared from infiltration by the cancer, making excision of the tumour feasible. Knowledge of these variations is also essential when whole and split liver transplantation is performed, and their presence often requires reconstruction.

The most common anatomical variants are a replaced or accessory left hepatic artery that arises from the left gastric artery, or a replaced or accessory right hepatic artery that arises from the superior mesenteric artery, both occurring in 10–20% of individuals.

Variations in the intrahepatic arteries are common and can be important surgically. For example, the segment IV artery most commonly arises from the left hepatic artery, but in up to 30% of cases it arises from the right hepatic artery or the proper hepatic artery ( ). The segment IV artery never arises to the right of the common hepatic duct, which means that if the right hepatic artery is divided to the right of the common hepatic duct, the arterial supply to segment IV is not endangered. Failure to recognize this variation can compromise the blood supply to segment IV following right hepatectomy, and it is especially important during right liver donation for live donor liver transplantation.

Splenic artery

The artery almost always arises from the coeliac trunk, in common with the left gastric and common hepatic arteries. However, it can originate from the common hepatic artery or the left gastric artery, or, rarely, directly from the abdominal aorta either in isolation or as a splenomesenteric trunk ( ). From its origin, the artery runs a little way inferiorly before turning to the left behind the stomach to run horizontally anterior to the left kidney and left suprarenal gland and behind or above the tail of the pancreas in the splenorenal ligament (see Fig. 68.6A ). Multiple loops or even coils of the artery appear above the superior border of the pancreas ( , ). The splenic artery gives off multiple small branches along its course that penetrate and supply the pancreas, including the dorsal pancreatic artery, the great pancreatic artery, arising approximately two-thirds of the way along the gland, and the artery to the tail of the pancreas, arising near the tail. These branches lie on or within the posterior aspect of the gland and often anastomose with the inferior pancreatic artery. Anatomical variations are not unusual, and the dorsal, great or inferior pancreatic arteries can be dominant in any one individual ( ). Near its termination, the splenic artery gives off the short gastric arteries and the left gastro-omental artery ( ). Additional variant branches include a posterior gastric artery and small retroperitoneal branches.

The splenic artery is one of the most tortuous arteries in the body (see Fig. 69.6 ). The reason for the tortuosity, which can become more pronounced with advancing age, is not understood, although there have been several proposals ( , , , , , ). The artery is 8–32 cm long and its calibre usually exceeds that of the common hepatic and left gastric arteries, which range from 3 to 12 mm. Splenic arterial blood flow is approximately 3 ml/sec/100 g, corresponding to approximately 7% of cardiac output ( , , , , , , ).

The splenic artery usually divides into two, or occasionally three, branches before entering the splenic hilum. The superior and inferior branches are sometimes known as superior and inferior polar arteries; as they enter the hilum they divide into four or five segmental arteries, each of which supplies a segment of splenic tissue. There is relatively little arterial collateral circulation between segments, which means that occlusion of a segmental vessel often leads to infarction of part of the spleen. Segmental arteries divide within the splenic trabeculae, becoming trabecular arteries. These leave the trabeculae and give rise to central arterioles that are surrounded by thick lymphoid sheaths of white pulp. Central arterioles ramify into several penicillar arterioles that feed the sinusoids of the red pulp. There is considerable communication among arterioles ( , , , , ).

Inferior pancreaticoduodenal artery

An inferior pancreaticoduodenal artery is present in most individuals. It usually arises either directly from the superior mesenteric artery at the inferior border of the pancreas or as a common vessel with the first jejunal artery (a pancreaticoduodenojejunal trunk) from the posterior or left aspect of the superior mesenteric artery ( , ). It runs to the right, posterior to the superior mesenteric vein, to reach the posterior surface of the uncinate process, where it divides into anterior and posterior inferior pancreaticoduodenal arteries. The smaller anterior pancreaticoduodenal artery passes to the right, immediately inferior and then anterior to the inferior border of the head of the pancreas, and runs superiorly to anastomose with the anterior superior pancreaticoduodenal artery and form the anterior pancreaticoduodenal arcade. The larger posterior branch runs posteriorly and to the right, posterior to the head of the pancreas, parallel and superior to the anterior inferior pancreaticoduodenal artery, and anastomoses with the posterior superior pancreaticoduodenal artery to form the posterior pancreaticoduodenal arcade ( ). Both branches supply the head of the pancreas, its uncinate process and the superior and descending parts of the duodenum. Occasionally the anterior and posterior pancreaticoduodenal arteries arise separately from the superior mesenteric or first jejunal artery. Multiple small arteries run between the anterior and posterior pancreaticoduodenal arcades, either via the pancreaticoduodenal groove or through the substance of the gland. The largest and most consistent of these is the communicating artery (sometimes known as the middle pancreaticoduodenal arcade) that passes between the pancreatic duct and accessory pancreatic duct and connects the anterior pancreaticoduodenal arterial arcade and the posterior superior pancreaticoduodenal artery ( ; see Fig. 68.6C ). This artery gives rise to most of the small arteries that supply the major duodenal papilla ( ).

When it arises as a pancreaticoduodenojejunal trunk, the inferior pancreaticoduodenal artery gives off a jejunal branch and then runs posterior to both the superior mesenteric artery and vein before dividing into its terminal branches. The inferior pancreaticoduodenal artery is at risk of bleeding during the retroperitoneal dissection of a Whipple procedure. Occasionally it is absent and the anterior and posterior inferior pancreaticoduodenal arteries arise separately from the superior mesenteric artery.

Jejunal branches

Usually, 4–6 jejunal branches arise from the left side of the proximal portion of the superior mesenteric artery (see Figure 64.13, Figure 64.14 ). They are distributed to the jejunum via 1–3 tiers of arterial arcades, the most distal of which gives rise to straight arteries. The latter run almost parallel in the mesentery before being distributed alternately to either side of the small intestine, forming two distinct ‘leaves’ of vessels within the mesentery separated by a relatively avascular plane (see Fig. 64.5A ). This vascular arrangement allows a dilated segment of small intestine to be bisected longitudinally and tubularized to double its length, a potentially useful technique for achieving small intestine lengthening in short bowel syndrome ( ). Small twigs from the jejunal arteries supply regional mesenteric nodes.

Branches from the first jejunal branch of the superior mesenteric artery supply the ascending part of the duodenum and frequently anastomose with a terminal branch of the anterior superior pancreaticoduodenal artery. The ascending part of the duodenum therefore receives a potential collateral supply from the coeliac trunk and superior mesenteric artery, which means that it is not commonly affected by ischaemia.

Ileal branches

Ileal branches are more numerous (around 8–12) and slightly smaller in calibre than jejunal branches. They arise from the left and anterior aspects of the superior mesenteric artery. The length of the mesentery from the superior mesenteric artery to the mesenteric border of the intestine is greater in the ileum, and so the branches form between two and six arcades before giving rise to multiple straight arteries that run directly towards the ileal wall (see Fig. 64.10B ). These branches run parallel in the mesentery and are distributed to both aspects of the ileum. They are shorter and thinner than their jejunal counterparts, particularly in the distal ileum, and do not form such distinct parallel ‘leaves’ of vessels. The terminal ileal arcades are supplied by the ileal branch of the ileocolic artery and the last ileal branch of the superior mesenteric artery (see Fig. 64.13 ). Few other vessels connect the ileocolic and superior mesenteric artery territories, and this makes surgical dissection of the ileocolic artery up to its origin relatively simple.

Ileocolic artery

The ileocolic artery arises from the superior mesenteric artery near the root of the mesentery of the small intestine, descending within that mesentery to the right towards the caecum, and crossing anterior to the right ureter, gonadal vessels and psoas major. It usually divides into superior and inferior branches, the superior branch running up along the left side of the ascending colon to anastomose with the right colic artery (or right branch of the middle colic artery) ( ). The inferior branch runs to the ileocaecal junction and divides into anterior and posterior caecal arteries, the appendicular artery, and an ileal branch that passes to the left in the ileal mesentery to anastomose with a terminal ileal branch of the superior mesenteric artery (see Fig. 65.23 ). The latter therefore provides a collateral arterial supply to the caecum. The ileocolic artery provides the major arterial supply to the caecum; traction on the caecum in the direction of the anterior superior iliac spine will cause the artery to tent up the mesentery, allowing the vessel to be easily identified.

The appendicular artery usually arises directly from the ileocolic artery and descends posterior to the terminal ileum to enter the meso-appendix a short distance from the base of the appendix (see Fig. 65.23 ). Here, it gives off a recurrent branch that anastomoses at the proximal appendix with a branch of the posterior caecal artery. The appendicular artery approaches the distal end of the organ, at first near to and then in the edge of the meso-appendix. Its terminal part lies on the wall of the appendix and can become thrombosed in appendicitis, resulting in distal gangrene or necrosis. Less commonly, the appendicular artery arises from the posterior caecal artery or an ileal artery ( ) (see Fig. 65.12 ). Accessory appendicular arteries are common; two or more arteries may supply the appendix.

Right colic artery

The right colic artery is relatively small and variable in its anatomy ( ). It usually arises as a common trunk with the middle colic artery, but can originate directly from the superior mesenteric artery or from the ileocolic artery (when it is referred to as an accessory right colic artery) (see Fig. 65.24 ). It passes to the right, across the right psoas major and quadratus lumborum, crossing the right gonadal vessels and ureter. Near the left side of the ascending colon it divides into a descending branch, which runs down to anastomose with the superior branch of the ileocolic artery, and an ascending branch, which passes up across the inferior pole of the right kidney to the right colic flexure, where it anastomoses with a branch of the middle colic artery. Together, these anastomoses form the marginal artery at the right colic flexure.

Middle colic artery

The middle colic artery arises from the right side of the superior mesenteric artery, either separately or in common with the right colic artery, just inferior to the neck of the pancreas, and passes anteriorly and superiorly within the transverse mesocolon, just to the right of the midline. As it approaches the colon, it usually divides into right and left branches. The right branch anastomoses with the ascending branch of the right colic artery. The left branch supplies the terminal part of midgut derivatives and anastomoses with a branch of the left colic artery near the left colic flexure. The marginal artery thus formed lies a few centimetres from the mesenteric edge of the transverse colon. Sometimes, the middle colic artery divides into three or more branches within the transverse mesocolon, in which case the most lateral branches form the arterial anastomoses. An accessory, or rarely a replaced, middle colic artery can arise directly from the abdominal aorta ( ), dorsal pancreatic, hepatic, inferior mesenteric or left colic arteries (see Fig. 65.25 ). In addition, an accessory middle colic artery is occasionally found arising from the superior mesenteric artery proximal to the origin of the actual middle colic artery ( ).

Left colic artery

The left colic artery usually arises from the inferior mesenteric artery shortly after its origin, ascends within the left colic mesentery and divides into an ascending and a descending branch (see Figure 65.38, Figure 65.39 ). The ascending branch passes upwards across the left psoas major, gonadal vessels, ureter and left kidney, and is crossed by the inferior mesenteric vein; its terminal branches anastomose with those of the left branch of the middle colic artery within the transverse mesocolon. The descending branch passes laterally and inferiorly and anastomoses with branches from the ascending branch and the most proximal sigmoid artery to form part of the marginal artery. The arterial arcades thus formed supply the distal third of the transverse and the descending colon. The left colic artery can originate from or in common with a sigmoid artery ( ). Occasionally an accessory, or rarely a replaced, left colic artery originates from the trunk of the superior mesenteric artery or its middle colic or first jejunal artery. When present, it runs laterally in the upper left colic mesentery just inferior to the duodenojejunal flexure to supply the proximal descending colon, and forms all or part of the marginal artery in the region of the distal transverse colon. The left colic artery can itself give rise to an accessory left middle colic artery. Occasionally it gives rise to a branch shortly after its origin, which ascends in the mesentery and anastomoses directly with a similar descending branch of the left branch of the middle colic artery (the so-called arc of Riolan; ).

The dominant arterial supply of the left colic flexure is usually from the left colic artery but can be from the left branch of the middle colic artery. The marginal artery in this region may be absent or small, but it can enlarge considerably if the inferior mesenteric artery is stenosed or occluded.

Sigmoid arteries

The inferior mesenteric artery gives rise to between two and five sigmoid arteries, which descend obliquely in the sigmoid mesocolon anterior to the left psoas major, ureter and gonadal vessels. They supply the distal descending colon and sigmoid colon and anastomose superiorly with the left colic artery and inferiorly with the superior anorectal artery. Unlike the arrangement in the small intestine, arterial arcades do not form until the arteries are close to the wall of the colon, when small branches arise to supply the sigmoid colon directly. A true marginal artery is less obvious in the sigmoid colon. There is often a significant interval in the mesentery between the highest sigmoid artery and the descending branch of the left colic artery; this forms a useful guide to the arterial territories during surgical dissection.

Superior anorectal artery

The principal arterial supply to the upper two-thirds of the rectum is via the superior anorectal artery (see Fig. 65.41 ). The inferior mesenteric artery crosses the left common iliac vessels medial to the ureter and descends in the medial limb of the sigmoid mesocolon, straddled by the hypogastric nerves on either side. As it crosses the linea terminalis it becomes the superior anorectal artery. At the level of the third sacral vertebra, where the rectum begins, the artery enters the proximal mesorectum in the midline and divides into two branches that descend, initially posterolaterally and then on each side of the rectum. Terminal branches pierce the rectal wall and anastomose with branches of the middle rectal and inferior anorectal arteries within the rectal submucosa.

The middle anorectal arteries arise from the internal pudendal, inferior gluteal, internal iliac arteries and less frequently from other internal iliac artery branches ( , ). When present, they enter the mesorectum anterolaterally in the ‘lateral ligaments’ and provide some additional supply to the middle third of the rectum.

Right common iliac artery

The right common iliac artery is approximately 5 cm long. It passes obliquely across part of the bodies of the fourth and the fifth lumbar vertebrae, and is crossed anteriorly by the sympathetic rami to the pelvic plexus and, at its division into internal and external iliac arteries, by the ureter. It is covered by the parietal peritoneum, which separates it from the small intestine. Posteriorly, it is separated from the bodies of the fourth and fifth lumbar vertebrae and the intervening intervertebral disc by the right sympathetic trunk, the terminal parts of the common iliac veins and the start of the inferior vena cava, the obturator nerve, lumbosacral trunk and iliolumbar artery. Laterally, the inferior vena cava and the right common iliac vein lie superiorly and the right psoas major lies inferiorly. The left common iliac vein is medial to the proximal part of the right common iliac artery.

Left common iliac artery

The left common iliac artery is shorter than the right and is approximately 4 cm long. Lying anteriorly are branches of the sympathetic trunk that contribute to the superior hypogastric plexus, the superior anorectal artery and, at its terminal bifurcation, the ureter. The sympathetic trunk, the bodies of the fourth and fifth lumbar vertebrae and the intervening intervertebral disc, the obturator nerve, lumbosacral trunk and iliolumbar artery are all posterior. The left common iliac vein is posteromedial and the left psoas major is lateral.

Superior vesical artery

The superior vesical artery is the first large branch of the anterior division. It lies on the lateral wall of the pelvis, just inferior to the linea terminalis, and runs anteroinferiorly, medial to the periosteum of the posterior surface of the pubis. It supplies the distal end of the ureter, the fundus of the urinary bladder, the proximal end of the ductus deferens and the seminal glands. It also gives origin to the umbilical artery in the fetus, which remains as a fibrous cord – the medial umbilical ligament – in the adult. This vessel occasionally remains patent as a small artery supplying the umbilicus.

The artery to the ductus deferens often originates from one of the branches of the superior vesical artery to the fundus of the urinary bladder: it accompanies the ductus deferens to the testis, where it anastomoses with the testicular artery.

Inferior vesical artery

The inferior vesical artery sometimes arises as a common branch with the middle anorectal artery from the internal iliac artery. In the male, it supplies the fundus of the urinary bladder, prostate, seminal glands and distal ureter and sometimes provides the artery to the ductus deferens. Branches to the prostate communicate across the midline. In the female it supplies the urinary bladder, and is often replaced by the vaginal artery ( ).

Middle anorectal artery

The middle anorectal artery runs into the lateral fascial coverings of the mesorectum. It often consists of multiple branches, can be small, and occasionally arises either close to or in common with the origin of the inferior vesical artery in males.

Vaginal artery

In females, the vaginal artery sometimes replaces the inferior vesical artery. It can arise from the uterine artery close to its origin as either a single vessel or multiple branches.

Obturator artery

The obturator artery arises from the anterior division of the internal iliac artery and runs anteroinferiorly on the lateral pelvic wall to the upper part of the obturator foramen. In the pelvis, it is related laterally to the obturator fascia and is crossed on its medial aspect by the ureter and, in the male, by the ductus deferens. The obturator nerve is superior to the artery, the obturator vein inferior to it. The obturator artery provides iliac branches to the iliac fossa that supply the underlying bone and iliacus and anastomose with the iliolumbar artery. It gives off a branch that runs medially to the urinary bladder and sometimes replaces the inferior vesical artery. In the female, the ovary lies medial to the obturator artery. A pubic branch usually arises just before the obturator artery leaves the pelvis and ascends over the pubis to anastomose with the contralateral artery and the pubic branch of the inferior epigastric artery.

The obturator artery leaves the pelvis via the obturator canal. It divides into anterior and posterior branches that encircle the obturator foramen between obturator externus and the obturator membrane. The anterior branch curves anteriorly on the membrane and then inferiorly along its anterior margin to supply branches to obturator externus, pectineus, adductors longus, brevis and magnus and gracilis. It anastomoses with the posterior branch and the medial circumflex femoral artery. The posterior branch follows the posterior margin of the obturator foramen, turning anteriorly on the ischial part to anastomose with the anterior branch. It supplies the muscles attached to the ischial tuberosity and anastomoses with the inferior gluteal artery. An acetabular branch enters the hip joint at the acetabular notch, ramifies in the fat of the acetabular fossa and sends a branch along the ligament of the head of the femur.

The obturator artery is occasionally replaced by an enlarged pubic branch of the inferior epigastric artery that descends almost vertically to the obturator foramen. It usually lies near the external iliac vein, lateral to the femoral ring, and is rarely injured during inguinal or femoral hernia surgery. It may curve along the edge of the lacunar ligament, partly encircling the neck of a hernia sac, and can be cut inadvertently during enlargement of the femoral ring in reducing a femoral hernia.

Uterine artery

The uterine artery is large and it usually arises inferior to the obturator artery on the lateral wall of the pelvis, running inferomedially within the cardinal ligament. It may arise directly from the internal iliac artery, the superior gluteal artery, obturator artery or from a common trunk with the internal pudendal artery ( ).

From its origin, the uterine artery crosses the ureter anteriorly in the broad ligament before branching as it reaches the uterus at the level of the cervico-isthmic junction (see Fig. 75.21 ). One major branch ascends the uterus tortuously within the broad ligament until it reaches the region of the hilum of the ovary, where it anastomoses with branches of the ovarian artery. Another branch descends to supply the cervix and anastomoses with branches of the vaginal artery to form two median longitudinal vessels, the azygos arteries of the vagina, which descend anterior and posterior to the vagina. Although there are anastomoses with the ovarian and vaginal arteries, the dominance of the uterine artery is indicated by its marked hypertrophy during pregnancy.

The tortuosity of the vessels as they ascend in the broad ligaments is repeated in their branches within the uterine wall. Each uterine artery gives off numerous branches. These enter the uterine wall, divide and run circumferentially as groups of anterior and posterior arcuate arteries. They ramify and narrow as they approach the anterior and posterior midline so that no large vessels are present in these regions. However, the left and right arterial trees anastomose across the midline and unilateral ligation can be performed without serious effects. Terminal branches in the uterine muscle are tortuous and are called helicine arterioles. They provide a series of dense capillary plexuses in the myometrium and endometrium. From the arcuate arteries, many helical arteriolar rami pass into the endometrium. Their detailed appearance changes during the menstrual cycle. Helical arterioles are less prominent during the proliferative phase, whereas they grow in length and calibre, becoming even more tortuous, during the secretory phase.

Internal pudendal artery

The internal pudendal artery is the smaller terminal branch of the anterior division of the internal iliac artery. Close to its origin it crosses anterior to piriformis, the sacral plexus and the inferior gluteal artery. It descends laterally to the inferior aspect of the greater sciatic foramen, where it leaves the pelvis between piriformis and ischiococcygeus and enters the gluteal region (see Fig. 75.4 ). It next curves around the posterior aspect of the ischial spine and enters the ischio-anal fossa via the lesser sciatic foramen. This course effectively allows the nerve to wrap around the posterior limit of levator ani at its attachment to the ischial spine. Posterior to the ischial spine, the artery is covered by gluteus maximus, the pudendal nerve is medial, and the nerve to obturator internus is lateral. The artery passes through the ischio-anal fossa in the pudendal canal (Alcock’s canal) in the fascia covering obturator internus, giving off the inferior anorectal artery early in its course through the fossa (see Fig. 71.12 ). It gives off several muscular branches in the pelvis and the gluteal region to supply adjacent muscles and nerves. The internal pudendal artery enters the perineum around the posterior aspect of the ischial spine and runs on the lateral wall of the ischio-anal fossa in the pudendal canal with the internal pudendal veins and the pudendal nerve. The canal lies about 4 cm superior to the inferior limit of the ischial tuberosity and is formed by connective tissue binding the internal pudendal vessels and pudendal nerve to the medial surface of the fascia covering obturator internus. As the artery approaches the margin of the ischial ramus, it proceeds superficial or deep to the perineal membrane, along the medial margin of the inferior pubic ramus, en route to its target structures.

In the male, the internal pudendal artery distal to the perineal artery gives a branch to the bulb of the penis before it divides into the deep and dorsal arteries of the penis (see Fig. 71.12 ). In the female, a similar branch of the internal pudendal artery is distributed to the corpus spongiosum and vagina. The deep arteries supply the corpora cavernosa of the clitoris; the dorsal arteries supply the glans and prepuce of the clitoris.

Branches of the internal pudendal artery are sometimes derived from an accessory pudendal artery, which is usually a branch of the internal pudendal artery before its exit from the pelvis.

Inferior gluteal artery

The inferior gluteal artery is the larger terminal branch of the anterior division of the internal iliac artery. It descends posteriorly, anterior to the sacral plexus and piriformis but posterior to the internal pudendal artery. It passes between either the first and second, or the second and third, sacral ventral rami, then between piriformis and ischiococcygeus, before running through the inferior aspect of the greater sciatic foramen to reach the gluteal region. It next runs inferiorly with the sciatic and posterior femoral cutaneous nerves, deep to gluteus maximus and between the greater trochanter and ischial tuberosity, and continues down the thigh, supplying the skin and anastomosing with branches of the perforating arteries. The inferior gluteal and internal pudendal arteries often arise as a common stem from the internal iliac artery, sometimes with the superior gluteal artery. In the pelvis, the inferior gluteal artery gives branches to piriformis, ischiococcygeus and iliococcygeus, and occasionally gives rise to the middle anorectal artery. It can supply vessels to the seminal glands and prostate.

Arteria comitans nervi ischiadici (artery to sciatic nerve)

The arteria comitans nervi ischiadici is a direct or indirect branch of the internal iliac artery, and runs on the surface of, or within, the sciatic nerve. It represents the primitive axial artery of the lower limb. The artery is usually a very small vessel; occasionally, it persists as a large vessel, in which case the femoral artery is correspondingly reduced in size. The artery may participate in collateral circulatory pathways.

Iliolumbar artery

The iliolumbar artery is the first branch of the posterior division of the internal iliac artery and ascends laterally anterior to the sacro-iliac joint and lumbosacral trunk. It lies posterior to the obturator nerve and external iliac vessels, and reaches the medial border of psoas major, dividing behind it into the lumbar and iliac branches. The lumbar branch supplies psoas major and quadratus lumborum, and anastomoses with the fourth lumbar artery. It sends a small spinal branch through the intervertebral foramen between the fifth lumbar and first sacral vertebrae to supply radicular branches to the cauda equina. The iliac branch supplies iliacus; between the muscle and bone it anastomoses with the iliac branches of the obturator artery. A large nutrient branch enters an oblique canal in the ilium. Other branches run around the iliac crest, contribute to the supply of gluteal and abdominal muscles, and anastomose with the superior gluteal, circumflex iliac and lateral circumflex femoral arteries.

Lateral sacral arteries

The lateral sacral arteries are usually double. If they are single, they soon divide into superior and inferior branches. The superior and larger branch passes medially into the first or second anterior sacral foramen, supplies the sacrum and contents of the sacral canal, and then leaves the sacrum via the corresponding dorsal foramen to supply the skin and muscles posterior to the sacrum. The inferior branch crosses obliquely anterior to piriformis and the sacral ventral rami, and then descends lateral to the sympathetic trunk to anastomose with its fellow and the median sacral artery anterior to the coccyx. Its branches enter the anterior sacral foramina and are distributed in the same way as the branches of the superior artery.

Superior gluteal artery

The superior gluteal artery is the largest branch of the internal iliac artery and effectively forms the main continuation of its posterior division. It runs posteriorly between the lumbosacral trunk and the first sacral ventral ramus, or between the first and second sacral ventral rami, and then turns slightly inferiorly, leaving the pelvis via the greater sciatic foramen above piriformis and dividing into superficial and deep branches. In the pelvis, it supplies piriformis, obturator internus and a nutrient artery to the ilium. The superficial branch enters the deep surface of gluteus maximus. Its numerous branches supply the muscle and anastomose with the inferior gluteal branches (see Fig. 77.47 ), while others perforate the tendinous medial attachment of the muscle to supply the skin over the sacrum, where they anastomose with the posterior branches of the lateral sacral arteries. The deep branch of the superior gluteal artery passes between gluteus medius and the ilium, soon dividing into superior and inferior branches. The superior branch skirts the superior border of gluteus minimus to the anterior superior iliac spine and anastomoses with the deep circumflex iliac artery and the ascending branch of the lateral circumflex femoral artery. The inferior branch runs through gluteus minimus obliquely, supplies it and gluteus medius, and anastomoses with the lateral circumflex femoral artery. A branch enters the trochanteric fossa to join the inferior gluteal artery and ascending branch of the medial circumflex femoral artery; other branches run through gluteus minimus to supply the hip joint.

The superior gluteal artery occasionally arises directly from the internal iliac artery with the inferior gluteal artery and sometimes from the internal pudendal artery.

Deep circumflex iliac artery

The deep circumflex iliac artery branches laterally from the external iliac artery almost opposite the origin of the inferior epigastric artery (see Fig. 76.4A ). It ascends and runs laterally to the anterior superior iliac spine deep to the inguinal ligament in a sheath formed by the union of the transversalis and iliac fasciae. There, it anastomoses with the ascending branch of the lateral circumflex femoral artery, pierces the transversalis fascia and skirts the inner lip of the iliac crest. About halfway along the iliac crest, it runs through transversus abdominis, and then between transversus abdominis and internal abdominal oblique, to anastomose with the iliolumbar and superior gluteal arteries. It gives off a large ascending branch at the anterior superior iliac spine that runs between internal abdominal oblique and transversus abdominis, supplies both muscles, and anastomoses with the lumbar and inferior epigastric arteries.

Inferior epigastric artery

The inferior epigastric artery originates from the external iliac artery posterior to the inguinal ligament. It curves forwards in the anterior extraperitoneal tissue, ascends obliquely along the medial margin of the deep inguinal ring, and continues as an artery of the anterior abdominal wall.

The inferior epigastric artery (often referred to as the deep inferior epigastric artery in clinical practice in order to distinguish it from the superficial (inferior) epigastric artery) originates from the medial aspect of the external iliac artery just proximal to where the vessels pass deep to the inguinal ligament (see Figure 60.1, Figure 60.2, Figure 60.3 ). Its accompanying veins, usually two, unite to form a single vein that drains into the external iliac vein ( ). The vessel curves forwards in the extraperitoneal tissue and ascends obliquely along the medial margin of the deep inguinal ring. It lies posterior to the spermatic cord, separated from it by the transversalis fascia. It pierces the transversalis fascia and enters the posterior layer of the rectus sheath by passing anterior to the arcuate line. In this part of its course it is visible through the parietal peritoneum of the anterior abdominal wall and with this covering forms the lateral umbilical fold. Disruption of the artery by surgical incisions (e.g. insertion of laparoscopic ports, surgical tacks or abdominal drains) can cause a haematoma, which can expand to considerable size because there is no adjacent tissue against which the bleeding can be tamponaded.

The ductus (vas) deferens in males or the round ligament of the uterus in females, pass medially after hooking around the inferior epigastric artery at the deep inguinal ring. The inferior epigastric vessels form the lateral border of the inguinal triangle (Hesselbach’s triangle). The boundaries of this anatomical region are seen during laparoscopic inguinal hernia repair: the inferior border of the triangle is formed by the iliopubic tract/inguinal ligament and the medial border by the lateral margin of rectus abdominis. Hernias occurring within the triangle are termed direct inguinal hernias.

The inferior epigastric arteries ascend and anastomose with their superior counterparts as a single vessel in only about 30% of cases ( ). Branching into two vessels before anastomosing is the most common pattern, accounting for almost 60%, with a trifurcation in the remainder. The inferior epigastric arteries have an average diameter of approximately 3 mm at their origin, compared to an average diameter of 1.6 mm at the origin of the superior epigastric arteries, presumably explaining why the inferior epigastric arteries provide the ‘dominant’ blood supply to rectus abdominis. Preliminary ligation of the inferior epigastric artery is often performed when preparing a myocutaneous flap from the mid or lower rectus abdominis based on the superior epigastric artery; this encourages augmentation of the superior epigastric arterial supply.

Branches of the inferior epigastric artery anastomose with branches of the superior epigastric artery within rectus abdominis at a variable level proximal to the umbilicus ( ). Other branches anastomose with terminal branches of the distal five posterior intercostal, subcostal and lumbar arteries at the lateral border of the rectus sheath. Inferolaterally, branches anastomose with the deep circumflex iliac artery. The inferior epigastric artery also gives off the cremasteric artery, a pubic branch, and muscular and cutaneous branches.