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Blood Supply of the Brain


Study Guidelines

  • 1.

    On simple outline drawings of the lateral, medial, and inferior surfaces of a cerebral hemisphere, learn to shade in the territories of the three cerebral arteries.

  • 2.

    Identify the main sources of arterial supply to the internal capsule.

  • 3.

    Become familiar with carotid and vertebral angiograms.

  • 4.

    Be able to list the territories supplied by the vertebral and basilar arteries.

  • 5.

    Identify the two blood–brain barriers. Be able to understand why shallow breathing following abdominal surgery in a critical patient may induce coma.

Because interpretation of the symptoms caused by cerebro-vascular accidents requires prior understanding of brain function, Clinical Panels on this subject are placed in the final chapter.

A Clinical Panel on blood–brain barrier pathology is placed in the present chapter because the symptoms are of a general nature.

The brain is absolutely dependent on a continuous supply of oxygenated blood. It controls the delivery of blood by sensing the momentary pressure changes in its main arteries of supply, the internal carotid and vertebral arteries. The arterial oxygen tension is controlled by a medullary chemosensitive area that monitors respiratory gas levels in the internal carotid artery and in the cerebrospinal fluid. The control systems used by the brain are exquisitely sophisticated, but they can be fatally affected due to poor perfusion as a result of a raptured arterial aneurysm or a thromboembolic phenomenon.

Arterial Supply of The Forebrain

The blood supply to the forebrain is derived from the two internal carotid arteries and from the basilar artery ( Fig. 4.1 ).

Fig. 4.1, (A) Brain viewed from below, showing background structures related to the circle of Willis. Part of the left temporal lobe (to the right of the picture) has been removed to show the choroid plexus in the inferior horn of the lateral ventricle. (B) The arteries comprising the circle of Willis. The four groups of central branches are shown; the thalamoperforating artery belongs to the posteromedial group, and the thalamogeniculate artery belongs to the posterolateral group. ACA , Anterior cerebral artery; ICA , internal carotid artery; MCA , middle cerebral artery; PCA , posterior cerebral artery.

Each internal carotid artery enters the subarachnoid space by piercing the roof of the cavernous sinus. In the subarachnoid space, it gives off ophthalmic , posterior communicating , and anterior choroidal arteries before dividing into the anterior and middle cerebral arteries .

The basilar artery divides at the upper border of the pons into the two posterior cerebral arteries . The cerebral arterial circle (circle of Willis) is completed by the union of the posterior communicating artery with the posterior cerebral artery on each side, and by the union of the two anterior cerebral arteries by the anterior communicating artery .

The choroid plexus of the lateral ventricle is supplied from the anterior choroidal branch of the internal carotid artery and by the posterior choroidal branch from the posterior cerebral artery.

Dozens of fine central (perforating) branches are given off by the constituent arteries of the circle of Willis. They enter the brain through the anterior perforated substance next to the optic chiasm and through the posterior perforated substance lying behind the mammillary bodies. (These designations refer to both the location on the ventral surface of the brain and the small perforations that appear when the numerous small penetrating arteries that supply these areas are pulled away from their points of entry.) These small perforating arteries have been classified in various ways but can be conveniently grouped into short and long branches. Short central branches arise from all the constituent arteries and from the two choroidal arteries. They supply the optic nerve, chiasm, and tract, and the hypothalamus. Long central branches arise from the three cerebral arteries. They supply the thalamus, corpus striatum, and internal capsule. They include the striate (lenticulostriate) branches of the anterior and middle cerebral arteries.

Anterior Cerebral Artery ( Fig. 4.2 )

The anterior cerebral artery passes above the optic chiasm to gain the medial surface of the cerebral hemisphere. It forms an arch around the genu of the corpus callosum, making it easy to identify in a carotid angiogram (see later). Close to the anterior communicating artery, it gives off the medial striate artery , also known as the recurrent artery of Heubner ( pronounced ‘Hoibner’), which contributes to the arterial blood supply of the internal capsule and the head of the caudate nucleus. Cortical branches of the anterior cerebral artery supply the medial surface of the hemisphere as far back as the parietooccipital sulcus ( Table 4.1 ). The branches overlap onto the orbital and lateral surfaces of the hemisphere.

Fig. 4.2, Medial view of the right hemisphere, showing the cortical branches and territories of the three cerebral arteries. ACA , Anterior cerebral artery; PCA , posterior cerebral artery.

Table 4.1
Named Cortical a Branches of the Anterior Cerebral Artery.
Branch Territory
Orbitofrontal Orbital surface of frontal lobe
Polar frontal Frontal pole
Callosomarginal Cingulate and superior frontal gyri; paracentral lobule
Pericallosal Corpus callosum

a The term cortical is conventional. Terminal is better, because these arteries also supply the underlying white matter.

Middle Cerebral Artery ( Fig. 4.3 )

The middle cerebral artery is the main continuation of the internal carotid, receiving 60% to 80% of the carotid blood flow. It immediately gives off important central branches and then passes along the depth of the lateral fissure to reach the surface of the insula. There it usually divides into upper and lower divisions. The upper division supplies the frontal and parietal lobes; the lower division supplies the parietal and temporal lobes and the mid-region of the optic radiation. Named branches and their territories are listed in Table 4.2 . Overall, the middle cerebral supplies two thirds of the lateral surface of the brain.

Fig. 4.3, Lateral view of the right cerebral hemisphere, showing the cortical branches and territories of the three cerebral arteries.

Table 4.2
Cortical Branches of the Middle Cerebral Artery.
Origin Branch(es) Territory
Stem Frontobasal Orbital surface of frontal lobe
Anterior temporal Anterior temporal cortex
Upper division Prefrontal Prefrontal cortex
Precentral Premotor areas
Central Pre- and postcentral gyri
Postcentral Postcentral and anterior parietal cortex
Parietal Posterior parietal cortex
Lower division Middle temporal Midtemporal cortex
Temporooccipital Temporal and occipital cortex
Angular Angular and neighbouring gyri

The central branches of the middle cerebral include the lateral striate arteries ( Fig. 4.4 ). These arteries supply the corpus striatum, internal capsule, and thalamus. Occlusion or rapture of a lateral striate artery causes a classic stroke syndrome (contralateral pure motor hemiplegia – paralysis of the arm, leg, and lower part of the face) due to loss of perfusion in the corticospinal tract in the posterior limb of the internal capsule.

Fig. 4.4, Distribution of perforating branches of the middle cerebral, anterior choroidal, and posterior cerebral arteries (schematic). The anterior choroidal artery arises from the internal carotid.

Note: Additional information on the blood supply of the internal capsule is provided in Chapter 35 .

Posterior Cerebral Artery ( Figs. 4.2 and 4.5 )

The two posterior cerebral arteries are the terminal branches of the basilar artery. However, in embryonic life they arise from the internal carotid, and in about 25% of individuals the internal carotid persists as the primary source of blood on one or both sides by way of a large posterior communicating artery .

Fig. 4.5, View from below the cerebral hemispheres, showing the cortical branches and territories of the three cerebral arteries. ACA , Anterior cerebral artery; ICA , internal carotid artery; MCA , middle cerebral artery; PCA , posterior cerebral artery.

Close to its origin, each posterior cerebral artery gives branches to the midbrain and a posterior choroidal artery to the choroid plexus of the lateral ventricle. Additionally, central branches pass through the posterior perforated substance ( Fig. 4.1 ). The main artery winds around the midbrain in company with the optic tract. It supplies the splenium of the corpus callosum and the cortex of the occipital and temporal lobes. Named cortical branches and their territories are shown in Table 4.3 .

Table 4.3
Named Cortical Branches of the Posterior Cerebral Artery.
Branch Artery Territory
Lateral Anterior temporal Anterior temporal cortex
Posterior temporal Posterior temporal cortex
Occipitotemporal Posterior temporal and occipital cortex
Medial Calcarine Calcarine cortex
Parietooccipital Cuneus and precuneus
Callosal Splenium of corpus callosum

The central branches, called thalamoperforating and thalamogeniculate , supply the thalamus, subthalamic nucleus, and optic radiation.

Note: Additional information on the central branches is provided in Chapter 35 .

Neuroangiography

The cerebral arteries and veins can be displayed under general anaesthesia by rapid injection of a radiopaque dye into the internal carotid or vertebral artery, followed by serial radiography every 2 seconds. The dye completes its course through the arteries, brain capillaries, and veins in about 10 seconds. The arterial phase yields either a carotid angiogram or a vertebrobasilar angiogram. Improved vascular definition in radiographs of the arterial phase or of the venous phase can be procured by a process of subtraction , whereby positive and negative images of the overlying skull are superimposed on one another, thereby virtually deleting the skull image.

A relatively recent technique, three-dimensional angiography , is based on simultaneous angiography from two slightly separate perspectives. In addition, with the use of magnetic resonance angiography (MRA) similar imagery of the intracranial and extracranial vessels can be obtained. The noninvasiveness of this method has resulted in its increasing use to substitute for conventional angiographic techniques.

Arterial phases of carotid angiograms are shown in Figs. 4.6 to 4.8 .

Fig. 4.6, Digital subtracted angiogram (DSA)—Arterial phase of a carotid angiogram, lateral view. Contrast medium injected into the left internal carotid artery is passing through the ACA and MCA. The base of the skull is shown in hatched outline. ACA , Anterior cerebral artery; ICA , internal carotid artery; MCA , middle cerebral artery.

Fig. 4.7, Digital subtracted angiogram (DSA)—Arterial phase of the right carotid angiogram, anteroposterior view. Note some perfusion of left anterior cerebral artery (ACA) territory (via the anterior communicating artery). ICA , internal carotid artery; MCA , middle cerebral artery.

Fig. 4.8, (A) Excerpt from a conventional carotid angiogram, antero-posterior view, showing an aneurysm attached to the middle cerebral artery. (B) Excerpt from a three-dimensional image of the same area. ACA , Anterior cerebral artery; ICA , internal carotid artery; MCA , middle cerebral artery.

Fig. 4.9 was taken at the parenchymal phase , when the dye is filling a web of minute terminal branches of the anterior and middle cerebral arteries, some of these anastomosing on the brain surface but most occupying the parenchyma (the cortex and subjacent white matter).

Fig. 4.9, Digital subtracted angiogram (DSA) — Parenchymal phase of a carotid angiogram, anteroposterior view. ACA , Anterior cerebral artery; ICA , internal carotid artery; MCA , middle cerebral artery.

Arterial Supply to The Hindbrain

The brainstem and cerebellum are supplied by the vertebral and basilar arteries and their branches ( Fig. 4.10 ).

Fig. 4.10, Arterial supply of hindbrain.

The two vertebral arteries arise from the subclavian arteries and ascend in the neck through the transverse foramina of the upper six cervical vertebrae. They enter the skull through the foramen magnum and unite at the lower border of the pons to form the basilar artery . The basilar artery ascends on the basilar surface of the pons and at its rostral end divides into two posterior cerebral arteries ( Figs. 4.11 and 4.12 ).

Fig. 4.11, Digital subtracted angiogram (DSA) — Vertebrobasilar angiogram, lateral view. Contrast medium was injected into the left vertebral artery. Basilar supply to the upper half of the cerebellum is somewhat obscured by overlying posterior parietal branches of the posterior cerebral artery. PCA , Posterior cerebral artery; PICA , posterior-inferior cerebellar artery.

Fig. 4.12, Digital subtracted angiogram (DSA)—Vertebrobasilar angiogram, Towne view (from above and in front), showing the vertebrobasilar arterial system. Note the large aneurysm arising from the bifurcation point of the basilar artery and accounting for the patient’s persistent headache. AICA , Anterior-inferior cerebellar artery; PICA , posterior-inferior cerebellar artery. (Angiogram kindly provided by Dr Pearse Morris, Director, Interventional Neuroradiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA.)

All primary branches of the vertebral and basilar arteries give branches to the brainstem and cerebellum.

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