Head and Neck Imaging


Temporal Bone

General

The temporal bone is divided into five portions:

    • Mastoid (posterolateral part that includes the mastoid process: attachment for sternocleidomastoid and other muscles)

    • Petrous portion (pyramidal-shaped medial part; inner ear structures, internal auditory canal [IAC], petrous apex)

    • Squamous portion (anterolateral part; forms lateral wall of middle cranial fossa)

    • Tympanic portion (forms bulk of external auditory canal [EAC] and middle ear space)

    • Styloid portion

External Auditory Canal (EAC)

    • Cartilaginous portion

    • Bony portion

Middle Ear ( Figs. 7.1 7.2 )

Composed of air-filled spaces that contain the ossicles and are divided into:

    • Epitympanum (attic; above imaginary line between scutum tip and tympanic facial nerve)

    • Mesotympanum (middle ear proper between epitympanum and hypotympanum)

    • Hypotympanum (shallow space below imaginary line between tympanic annulus and cochlear promontory)

FIG. 7.1

FIG. 7.2

Boundaries of the middle ear are tympanic membrane (TM) laterally, the tegmen superiorly, and the inner ear medially. Posteriorly, there are three important structures (facial nerve recess, pyramidal eminence, and sinus tympani). The eustachian tube (pressure equalization) connects the middle ear with the nasopharynx. The lateral epitympanic recess (Prussak space) is a common location for retraction pockets and cholesteatoma. Three ossicles transmit sound waves from the TM to the oval window in the vestibule:

    • Malleus

    • Incus

    • Stapes (two crura, one footplate)

Inner Ear ( Fig. 7.3 )

The inner ear (labyrinth) consists of:

    • Three semicircular canals, which connect to vestibule

    • Vestibule (utricle and saccule) between semicircular canals and cochlea

    • Cochlea (sensorineural hearing), which connects to:

      • Stapes → oval window

      • Round window (allows for counterpulsation of fluid)

FIG. 7.3

Internal Auditory Canal (IAC) ( Fig. 7.4 )

Left and right IAC should not differ >2 mm in diameter. Contents of IAC are divided by the falciform crest and Bill bar:

    • Facial nerve (anterior superior): cranial nerve (CN) VII (“7 up”)

    • Cochlear part (anterior inferior): CN VIII (“Coke down”)

    • Superior vestibular nerve (posterior): CN VIII

    • Inferior vestibular nerve (posterior): CN VIII

FIG. 7.4

Facial Nerve ( Figs. 7.5 7.6 )

Four main parts of the facial nerve:

    • Intraaxial segment

    • Cisternal segment

    • Intratemporal segment:

      • Meatal (IAC) segment

      • Labyrinthine segment

      • Tympanic (horizontal) segment

      • Mastoid (vertical) segment

    • Extracranial segment:

      • Exits the skull through the stylomastoid foramen

      • Immediately gives off the posterior auricular branch/nerve

FIG. 7.5

FIG. 7.6

Main trunk courses through the parotid gland and gives rise to five terminal branches. The intratemporal segment of the facial nerve gives rise to three branches (see Fig. 7.6 ):

    • Greater superficial petrosal nerve

    • Stapedius nerve

    • Chorda tympani nerve

Hearing Loss

Types

    • Conductive

      • Disruption of sound conduction that may be secondary to abnormalities in the EAC, TM, ossicles, or oval window

      • Common underlying causes: otitis, cholesteatoma, otosclerosis, trauma

    • Sensorineural

      • Evaluate inner ear, IAC

      • Common underlying causes: idiopathic, hereditary, vestibular Schwannoma, enlargement of vestibular aqueduct, labyrinthitis ossificans, otosclerosis (cochlear otosclerosis), trauma

Pulsatile Tinnitus

Causes

    • Normal vascular variants

      • Aberrant ICA

      • Jugular bulb anomalies (high or dehiscent jugular bulb, diverticulum)

      • Persistent stapedial artery

    • Vascular tumors

      • Glomus jugulare paraganglioma

      • Glomus tympanicum

    • Vascular abnormalities

      • Skull base dural arteriovenous fistula/arteriovenous malformation (AVM)

      • Atherosclerotic carotid artery stenosis

      • Carotid-cavernous fistula (CCF)

      • ICA dissection or aneurysm at the petrous apex

      • Fibromuscular dysplasia

      • Dural sinus stenosis

      • Transverse-sigmoid sinus diverticulum

    • Other causes of tinnitus

      • Idiopathic intracranial hypertension

      • Paget disease

      • Otosclerosis

      • Ménière disease

Trauma

Temporal Bone Fractures

Clinical Findings

    • Periauricular swelling and ecchymosis (Battle sign)

    • Bleeding into EAC or hemotympanum

    • Hearing loss

    • Tinnitus

    • Vertigo

    • Cerebrospinal fluid (CSF) leak

    • Facial paresis

Radiographic Features

TEMPORAL BONE FRACTURES a ( Fig. 7.7 )
Parameter Longitudinal Fractures Transverse Fractures
Frequency 80% 20%
Fracture line Parallel to long axis Perpendicular to long axis
Typically involves Middle ear Inner ear
Labyrinth Typically spared Commonly involved
Ossicles Involved: conductive hearing loss Commonly spared
Tympanic membrane Involved Frequently spared
Facial paralysis Approx. 20% Approx. 50%
More clinically relevant classification may be otic capsule (osseous labyrinth) violating versus otic capsule sparing. Otic capsule involvement increases the risk of sensorineural hearing loss, seventh cranial nerve injury, and cerebrospinal fluid leak.

a Fractures may also be characterized as oblique: mixed features of longitudinal and transverse fractures, cross the petrotympanic fissure.

FIG. 7.7

Fracture Complications

    • Ossicular fractures or dislocations

    • TM perforation

    • Hemotympanum

    • CN VII paralysis

    • CSF otorrhea

    • Meningitis, abscess

    • Sinus thrombosis, rare

    • Labyrinthitis ossificans (late)

    • Also assess for associated cervical spine fracture or fracture extension to carotid canal.

Indications for Surgery in Temporal Bone Fractures

    • Ossicular fracture or dislocation: varied, conservative or surgery

    • Facial nerve injury: frequently conservative, but occasionally requires surgical decompression

    • Labyrinthine fistulae: surgery if persistent

    • CSF leaks: surgery if persistent

Inflammation

Acute Inflammation

    • Otitis media (fluid in the middle ear cavity): acute, subacute, chronic forms

    • Children: common

    • Adults: less common; exclude nasopharyngeal carcinoma (NPC), which can cause eustachian tube obstruction and serous otitis media.

    • Mastoiditis: fluid-filled mastoid cells are also often present but not specific for infection.

    • Coalescent mastoiditis: occurs if medical treatment of acute otomastoiditis fails. Enzymatic resorption of mastoid septa and development of an intramastoid empyema seen as erosive changes on computed tomography (CT); comparison with the opposite side can be helpful in subtle cases.

    • Labyrinthitis

Potential Complications

    • Meningitis

    • Subdural empyema or epidural abscess

    • Dural venous sinus thrombosis

    • Petrositis (infection of petrous air cells)

    • Gradenigo syndrome (rare complication of petrositis: triad of otomastoiditis, sixth nerve palsy, and pain in the distribution of the fifth nerve)

    • Subperiosteal or Bezold (via defect at the mastoid tip) abscess

    • Focal encephalitis, brain abscess, otitic hydrocephalus

Bell Palsy

Acute onset peripheral facial nerve palsy secondary to herpes simplex virus (HSV) that the majority of time resolves within 2 to 3 months. Imaging typically performed for atypical or persistent palsy. By magnetic resonance imaging (MRI), there is enhancement along the facial nerve involving intracanalicular (“fundal tuft”) and labyrinthine segments that normally do not enhance. Note that mild enhancement of the tympanic and mastoid segments of the facial nerve can be seen as a normal finding due to vascular supply. Facial nerve enhancement is nonspecific and can occur in other inflammatory and neoplastic conditions (especially if the nerve is enlarged, consider secondary to perineural spread of a tumor).

Acquired Cholesteatoma ( Fig. 7.8 )

Mass of stratified squamous epithelium and keratin debris. Cause: epithelial cells accumulate in the middle ear via a perforation of the TM. The most accepted theory is that they arise from TM retraction pockets resulting from decreased intratympanic pressure. Types:

    • Acquired (98%): chronic middle ear infection (common). Arise in attic (Prussak space; pars flaccida cholesteatoma), or from pars tensa (sinus tympani).

    • Congenital (epidermoid; 2%): cholesteatoma arises from epithelial nests in middle ear, mastoid, or petrous bone, including the labyrinth (uncommon).

FIG. 7.8

Radiographic Features

    • High resolution temporal bone CT first line, excellent for detailed bone evaluation; MRI can be helpful for complex cases and cholesteatoma distinction.

    • Soft tissue mass in middle ear

    • Borders may be well- or ill-defined.

    • Erosion of incus and otic spur (scutum) common

    • Bone resorption (collagenase) is typical and occurs most commonly in:

      • Ossicles

      • Lateral semicircular canal (fistula)

      • Tegmen tympani

      • Facial canal

    • Mastoid air cells may be underpneumatized and sclerotic secondary to chronic infection.

    • Labyrinthine fistula formation in lateral semicircular canal is less common.

    • It is often impossible to distinguish chronic middle ear infection from cholesteatoma in cases with little bone destruction on CT. However, MRI can be useful for distinction of cholesteatoma (restricted diffusion, no enhancement) from inflammatory changes or granulation tissue (enhances).

LOCATION OF ACQUIRED CHOLESTEATOMA
Parameter Attic Cholesteatoma Sinus Cholesteatoma
TM perforation Pars flaccida Pars tensa
Location Prussak's space Sinus tympani
Ossicles displaced Medially Laterally
Bone erosion Lateral tympanic wall (erosion of scutum is an early finding) Initially subtle
Ossicle erosion Head of malleus and long process of incus Short process of incus and stapes
TM, Tympanic membrane.

Complications of Acquired Cholesteatoma

    • Labyrinthine fistula (dehiscence of semicircular canals—most frequently lateral canal)

    • Facial nerve paralysis (involvement of facial nerve canal)

    • Invasion of tegmen tympani, petrous apex, or sigmoid plate

    • Automastoidectomy

Congenital Cholesteatoma (Epidermoid)

Constitute approximately 2% of temporal bone cholesteatomas and may affect middle ear, EAC, mastoid, or petrous bone, including the labyrinth (uncommon). The most common location is the anterosuperior portion of the middle ear near the eustachian tube or stapes. The typical presentation is in a young patient with otherwise normal mastoid pneumatization and without history of chronic ear infections. Histologically, the cholesteatoma is made up of squamous cell lining, keratin debris, and cholesterol.

Cholesterol Granuloma (Cholesterol Cysts)

Mix of hemorrhage, cholesterol crystals, and granulation tissue that may be present in temporal bone, including the petrous apex or rarely the middle ear. Depending on the location of the expansile erosive lesion and involvement of critical structures, they can be associated with hearing loss, tinnitus, and CN palsies.

Radiographic Features

    • Expansile erosive osseous lesion of the petrous apex

    • Smooth margins

    • CT: isodense relative to brain, no enhancement, no calcification

    • MRI: hyperintense relative to brain on T1-weighted (T1W) images because of methemoglobin and cholesterol crystals

    • Cholesterol granulomas retain their high signal on fat suppressed T1W images, distinguishing them from fatty lesions.

SIGNAL CHARACTERISTICS RELATIVE TO BRAIN
Epidermoid (Congenital Cholesteatoma) Cholesterol Granuloma (Cholesterol Cyst) Mucocele a
CT Isodense, no calcium, no enhancement < or occasionally >
T1W ≤ (lamination) > (cholesterol) ≤ or occasionally >
T2W > > (with peripheral low signal hemosiderin ring) > or occasionally <
CT , Computed tomography; MRI , magnetic resonance imaging; T1W , T1-weighted; T2W , T2-weighted.

a Density and MRI signal characteristics of mucoceles can vary depending on protein content.

Malignant or Necrotizing External Otitis

  • Severe, life-threatening Pseudomonas aeruginosa infection in older adults with diabetes. Aggressive infection of EAC, adjacent soft tissues, and skull base that spreads via cartilaginous fissures of Santorini and can extend into:

    • Middle ear and mastoid air cells

    • Variable involvement of skull base, including osteomyelitis

    • Phlegmon and abscesses may spread in any direction:

      • Parapharyngeal, parotid, or masticator space

      • Intracranially

      • Anteriorly to temporomandibular joint (TMJ)

Radiographic Features

    • Early findings may manifest as thickened mucosa of EAC and soft tissue swelling; more advanced disease can have bone erosion associated with the opacification.

    • Mastoiditis

    • Skull base osteomyelitis

    • Sinus phlebitis and thrombosis

    • Phlegmon or abscess in nearby soft tissues and spaces

Labyrinthitis Ossificans

Ossification of the membranous labyrinth as a sequela of previous infectious, inflammatory, traumatic, or surgical injury to the inner ear. Seen as ossification within the membranous labyrinth on high resolution computed tomography (HRCT) and foci of low signal on T2-weighted (T2W) MRI within the otherwise high signal fluid of the membranous labyrinth.

Tumors

Glomus Tumors

Glomus tumors (chemodectomas) arise from chemoreceptor cells in multiple sites in the head and neck. The majority are benign and approximately 10% are multiple; thus it is important to check other common locations in the head and neck during imaging (glomus jugulare, vagale, and carotid body tumor). Glomus tympanicum represents the most common middle ear tumor.

Types

    • Glomus jugulare: origin at jugular bulb; more common

    • Glomus tympanicum: arises from paraganglia along inferior tympanic nerve (Jacobson nerve), frequently on the cochlear promontory

    • Glomus vagale

    • Carotid body tumor

Clinical Findings

    • Pulsatile tinnitus (most common)

    • Conductive hearing loss

    • Rarely, facial nerve paralysis

    • Other focal neurologic symptoms depending on location as well as systemic symptoms such as sudden blood pressure (BP) fluctuations if the tumor secretes catecholamines

Radiographic Features

    • Glomus tympanicum typically presents as a small enhancing soft tissue mass centered over the cochlear promontory. Enhancement distinguishes tumors from obstructive secretions.

    • Glomus jugulare (glomus jugulotympanicum) is centered in the region of the jugular foramen. Most common path of spread is to the middle ear. It is accompanied by permeative bone changes in the jugular foramen. Characteristic findings by MRI are multiple low signal intensity areas that represent flow voids in the tumor. This has a salt-and-pepper appearance.

    • Glomus vagale paraganglioma: arises from paraganglia in the nodose ganglion of the vagus nerve in the nasopharyngeal carotid (or poststyloid parapharyngeal) space; displaces carotid anteromedially, jugular vein posterolaterally, and does not splay the carotid bifurcation.

    • Carotid body paraganglioma: arises from carotid glomus bodies (paraganglia); splays the external carotid artery (ECA) and internal carotid artery (ICA).

    • Intense contrast enhancement by CT, MRI, angiography

    • Large tumors erode bone.

Other Benign Temporal Bone Tumors

    • Meningioma

    • Facial schwannoma may arise anywhere along the course of CN VII. In the IAC, the tumor may be indistinguishable from a vestibular schwannoma unless it can be seen to arise from the facial nerve.

    • Osteoma

    • Adenoma (ceruminoma), benign but locally aggressive, rare

    • Endolymphatic sac tumor, benign but locally aggressive; permeative destructive lesion with spiculated calcified tumor matrix

    • Epidermoid (primary cholesteatoma): not a true neoplasm

Malignant Temporal Bone Tumors

    • Carcinoma (CA) (most common malignant tumors)

      • Squamous cell carcinoma (SCC) arising from the EAC

      • Adenocarcinoma

    • Lymphoma

    • Metastases: breast, lung, renal, prostate; neuroblastoma and leukemia in children

    • Chondrosarcoma, other primary bone tumors

    • Rhabdomyosarcoma in children and late teens

Otodystrophies and Dysplasias

Otosclerosis (Otospongiosis)

The osseous labyrinth (otic capsule) is the normal dense bone of the inner ear surrounding the cochlea, vestibule, and semicircular canals. In otosclerosis, the capsule is replaced by vascular, irregular bony trabeculae (lucent on CT) and later by new bone within the lucent areas in the late, chronic healing phase. Unknown cause, sporadic or autosomal dominant (AD) gene transmission, frequently bilateral. Patients (female > male) present with progressive conductive or mixed hearing loss.

Types

    • Fenestral: sclerosis or spongiosis around oval window, including fixation of stapes. Diagnosis is usually made from clinical and audiometric findings (conductive hearing loss). Begins as radiolucent focus at the anterior margin of the oval window. Early disease may not be seen on imaging or may be very subtle.

    • Cochlear (retrofenestral) otosclerosis: involves pericochlear bony labyrinth. CT findings:

      • Deossification around cochlea (lucent halo)

      • Sclerosis occurs later in disease (mixed lucencies and densities)

    • Disease begins at fissula ante fenestram (fenestral); fenestral alone most common (85%, conductive hearing loss); approximately 15% progress to cochlear (mixed hearing loss).

Semicircular Canal Dehiscence Syndrome

CT shows a small defect or dehiscence in the bony wall of the superior or less commonly posterior semicircular canal. Seen as ≥2 mm dehiscence of roof of superior semicircular canal on coronal or ideally transverse oblique (Poschl) CT reformats for superior semicircular canal dehiscence. Clinically presents with dizziness and vertigo +/– nystagmus with loud sound or pressure (Tullio phenomenon). Clinical syndrome + positive CT = semicircular canal dehiscence syndrome. Can also be associated with inner ear conductive hearing loss. The cause is unknown, likely developmental, possibly also secondary to trauma.

Other Otodystrophies and Dysplasias

    • Paget disease

    • Fibrous dysplasia

    • Osteogenesis imperfecta

    • Skull base osteopetrosis

    • Craniometaphyseal dysplasia (Pyle disease)

    • Craniodiaphyseal dysplasia and Camurati-Engelmann disease (progressive diaphyseal dysplasia)

    • Cleidocranial dysostosis

Congenital Anomalies

Congenital Abnormalities of the Inner Ear

    • Cochlear incomplete partition type I: spectrum of abnormalities ranging from lack of internal structure of the cochlea to severe cystic cochleovestibular malformation

    • Cochlear incomplete partition type II: incomplete partition with deficient interscalar septum between middle and apical turns (Mondini anomaly: historic terminology – incomplete partition type II + large vestibular aqueduct)

    • Cochlear hypoplasia: small, underdeveloped cochlea, typically <2 turns

    • Cochlear aplasia: absent cochlea with variable anomalies of other inner ear structures

    • Labyrinthine aplasia: aplasia or hypoplasia of otic capsule, petrous apex hypoplasia, and other associated temporal bone abnormalities (Michel aplasia: historic terminology for complete labyrinthine aplasia)

    • Common cavity malformation: undifferentiated cochlea and vestibule represented by a common cavity of variable size.

    • Large vestibular aqueduct: ≥1 mm diameter at midpoint and/or ≥2 mm at operculum perpendicular to long axis of vestibular aqueduct; rule of thumb—abnormal if larger than the posterior semicircular canal. High incidence of associated cochlear abnormalities (also see incomplete partition II above).

    • Small IAC

Petrous Malformations Associated With Recurrent Meningitis

    • The presence of a fistula in the petrous portion of the temporal bone may lead to otorrhea, pneumocephalus, meningitis, or abscess; rare.

    • Acquired lesion of the petrous apex can potentially have similar complications depending on extent and violation of adjacent structures.

Overview of Syndromes

SYNDROMES ASSOCIATED WITH VARYING DEGREES OF DEAFNESS a
Syndrome/Disease Inner Ear Middle Ear Outer Ear Other Abnormalities
Otocraniofacial
Treacher-Collins syndrome ++ ++ ++ Coloboma, mandibular hypoplasia (micrognathia), microtia
Otocervical
Klippel-Feil syndrome ++ ++ ++ Cervical fusion, short neck, low posterior hairline, limited cervical motion
Cleidocranial dysplasia (dysostosis) + + ++ Hypoplastic, malformed, or absent clavicles; large head, underdeveloped facial bones
Otoskeletal
Osteogenesis imperfecta ++ + Fractures, blue sclera in some subtypes
Osteopetrosis + ++ ++ Autosomal recessive: macrocephaly, deafness and blindness; autosomal dominant much less severe, may even be asymptomatic
Other
Hemifacial macrosomia (Goldenhar syndrome, oculoauriculovertebral spectrum) + ++ ++ Facial asymmetry, microtia, variable ocular abnormalities, cervical spine deformity
CHARGE ++ ++ ++ Coloboma, heart anomaly, choanal atresia, mental retardation, genital hypoplasia
Pendred syndrome ++ Thyroid organification defect with goiter
Branchio-oto-renal syndrome ++ ++ ++ Branchial and renal anomalies
Thalidomide ++ ++ ++ Short limbs, cardiac and GI abnormalities
GI , Gastrointestinal.

a There can be variations in the type and extent of otologic abnormalities associated with each syndrome.

Skull Base, Foramina, and Cranial Nerves

General

Anterior and Central Skull Base Anatomy

    • Anterior skull base: broadly consists of floor of anterior cranial fossa and the roof of the nose, ethmoid air cells, and orbits.

    • Central skull base: broadly consists of floor of middle cranial fossa, roof of sphenoid sinus, and greater wing of sphenoid.

    • Anterior and central skull base boundary:

      • Medially: posterior margin of planum sphenoidale (tuberculum sellae)

      • Laterally: lesser wing of sphenoid/sphenoid

Central Nervous System (CNS), Foramina, and Cavernous Sinus ( Figs. 7.9 7.10 )

    • CN I: olfactory nerve

      FIG. 7.9

      FIG. 7.10

    • CN II: optic nerve

    • CN III: oculomotor nerve

    • CN IV: trochlear nerve

    • CN V: trigeminal nerve

    • CN VI: abducens nerve

    • CN VII: facial nerve

    • CN VIII: auditory nerve

    • CN IX: glossopharyngeal nerve

    • CN X: vagus nerve

    • CN XI: spinal accessory nerve

    • CN XII: hypoglossal nerve

OVERVIEW OF FORAMINA
Opening Cranial Nerve Artery Vein
Optic canal II Ophthalmic artery
Superior orbital fissure III, IV, V1, VI Orbital branches of middle meningeal artery (occasionally), recurrent meningeal branches of lacrimal artery Ophthalmic veins
Inferior orbital fissure Infraorbital nerve (V2) Infraorbital artery Ophthalmic vein (inferior division)
Carotid canal Sympathetic plexus ICA
Foramen rotundum V2 Artery of foramen rotundum Emissary veins
Foramen ovale V3 Accessory meningeal artery Emissary veins
Foramen spinosum Meningeal (recurrent) branch of mandibular nerve, lesser petrosal nerve (occasionally) Middle meningeal artery Middle meningeal vein
Foramen lacerum (not a true foramen) Nerve of the pterygoid canal (formed by greater petrosal and deep petrosal nerves) Terminal (meningeal) branches of ascending pharyngeal artery Emissary veins
Vidian (pterygoid) canal Vidian nerve Vidian artery Vidian vein
Stylomastoid foramen VII Stylomastoid artery
Jugular foramen pars nervosa IX, Jacobson nerve Inferior petrosal sinus
Jugular foramen pars vascularis X, XI, Arnold nerve Posterior meningeal artery Jugular bulb
Hypoglossal canal XII
ICA , Internal carotid artery.

Pterygopalatine Fossa (PPF) (see Fig. 7.10 )

    • Important space and potential route of spread of disease in the deep face

    • Contents:

      • Pterygopalatine ganglion

      • Maxillary nerve (V2) via foramen rotundum

      • Distal internal maxillary artery via pterygomaxillary fissure

    • Relations and boundaries:

      • Anterior: posterior maxillary sinus wall

      • Posterior: pterygoid plates and inferior part of lesser wing of sphenoid

      • Superior: inferior orbital fissure

      • Inferior: tapers into the greater palatine canal

      • Medial wall: perpendicular plate of palatine bone, sphenopalatine foramen superiorly

      • Lateral wall: pterygomaxillary fissure (vertical communication with infratemporal fossa)

Anterior Skull Base Lesions

Lesion affecting the anterior skull base can be centered in the bone, arise in the anterior cranial fossa above, or arise from sinonasal cavities below; localization of lesion center can help with the differential.

Neoplasms: Benign and Malignant

    • Meningioma: classic locations olfactory groove and planum sphenoidale

    • Olfactory neuroblastoma (esthesioneuroblastoma): malignant tumor arising from olfactory mucosa in superior nasal cavity

      • Heterogeneously enhancing mass in upper nasal cavity

      • Larger tumors extend to the floor of anterior cranial fossa with erosive bone changes.

      • May have “waist” at level of cribriform plate

      • Peripheral tumor cysts at intracranial tumor-brain margin are highly suggestive of diagnosis.

    • Osteoma (sinonasal): well-defined nonaggressive bony mass, most common in frontal and ethmoid sinuses.

    • Metastasis: bone destruction, may involve dura or brain parenchyma

    • Sinonasal SCC: most common primary sinonasal malignancy, ethmoid sinus and nasal cavity primaries may extend to the anterior skull base.

      • Aggressive lesion with bone destruction

    • Sinonasal undifferentiated CA: rare, highly aggressive sinonasal malignancy

    • Sinonasal lymphoma: cephalad extension from nasal cavity through skull base

      • Typically, homogeneous lesions with relatively high density on unenhanced CT

      • Septal destruction, occasional bone remodeling

      • On MRI, relatively low signal on T2W images, homogeneously enhancing

    • Sinonasal melanoma: highly malignant, nasal cavity often site of origin

      • Bone destruction more frequent than remodeling

      • On MRI lesions may have intrinsically high signal on T1W and low signal on T2W images (paramagnetic properties of melanin)

      • Avid enhancement

    • Hemangiopericytoma: hypervascular lesion with aggressive growth pattern

      • Dural-based mass that may have internal flow voids

      • Intensely enhancing

    • Sinonasal nerve sheath tumor: benign neoplasm arising from peripheral nerve Schwann cells

      • Well-defined lesion with smooth remodeling

      • Enhancing sharply marginated mass, may have internal cystic changes

Nonneoplastic Lesions

    • Fibrous dysplasia: expansile developmental bone lesion

      • Classically ground-glass matrix (varies depending on amount of fibrous and ossified components)

      • Enhancing lesion, can be deceptively aggressive on MRI (suspect if very low signal on T1 and T2)

      • Obtain CT to demonstrate typical characteristics

    • Mucocele: expanded sinus from chronic obstruction

      • Variable signal depending on protein content of secretions

      • No solid enhancement (can see mucosal enhancement around the margins)

      • Nonaggressive with bone remodeling, MRI highly accurate for distinguishing higher density/proteinaceous secretions that are equivocal on CT from solid masses.

    • Meningocele and encephalocele: extension of meninges ± brain parenchyma through skull base defect into nasal cavity or ethmoidal labyrinth

      • CT frequently shows bone defect.

      • High resolution MRI for confirmation

      • Heavily T2W high resolution sequences can be helpful for clear demonstration of extension of meninges and/or brain through defect.

    • Nasal dermal sinus: midline developmental lesion anywhere from nasal tip to anterior skull base at foramen cecum, may be associated with nasal pit or repetitive bouts of meningitis clinically.

      • Look for tract from nasal lesion to anterior cranial fossa.

      • May see widened foramen cecum ± bifid crista galli

      • May have associated dermoid/epidermoid along tract

Central Skull Base Lesions

Lesions may arise from central skull base components, represent inferior extension from above or superior extension from below. Characterization of calcified matrix can help in the diagnosis of cartilaginous lesions and is best seen on CT.

Neoplasms: Benign and Malignant

    • Metastasis: suspect in patient with known malignant neoplasm with new craniofacial pain or cranial neuropathy

      • Lytic destructive lesion

      • May have associated soft tissue mass

      • Look for multiple lesions

    • Meningioma: in addition to those with a classic appearance, occasionally lesions can be infiltrative, extend to extracranial spaces such as pterygopalatine and infratemporal fossa, or have intraosseous component.

    • Multiple myeloma: commonly lytic, multiple, may be indistinguishable from extensive metastatic disease with lytic pattern.

    • Lymphoma: may originate in bone or from dura, wide range of appearances.

      • Typically enhance uniformly

      • Can be dural-based

      • Can involve bone with lytic changes

      • Extensive soft tissue mass

      • Relatively restricted diffusion with low apparent diffusion coefficient (ADC) values

    • Pituitary macroadenoma: may occasionally extend inferiorly into clivus or sphenoid sinus.

    • Chordoma (clivus): rare, locally aggressive tumor arising from primitive notochord remnants

      • May present with headaches and diplopia secondary to CN VI involvement in Dorello canal, other nerves can be involved depending on extent.

      • Expansile destructive midline clival mass, may be near sphenooccipital synchondrosis

      • Classically high signal on T2W images secondary to high water content

      • Can also have mix of calcification, hemorrhage, and mucoid material with increased T1 and decreased T2 signal

      • Enhancing lesion, sometimes in a “honeycomb” pattern

    • Chondrosarcoma: arises in skull base fissures and synchondroses, most commonly petrooccipital fissure.

      • Typically eccentric (in contradistinction to chordoma)

      • Chondroid ring and arc-like calcifications on CT

      • Heterogeneously enhancing with high T2 signal with scattered hypointense foci (calcifications) on MRI

    • Langerhans cell histiocytosis: lytic enhancing lesion typically presenting in the first decade of life

Nonneoplastic Lesions

    • Fibrous dysplasia: relatively common expansile bone lesion

      • Classically ground-glass matrix (varies depending on amount of fibrous and ossified components)

      • Enhancing lesion, can be deceptively aggressive on MRI (suspect if very low signal on T1 and T2)

      • Obtain CT to demonstrate typical characteristics

    • Paget disease: primary metabolic bony disease, often asymptomatic, typically seen in older adults, more common in males

      • May be multifocal disease, with mixed lytic-sclerotic pattern

      • Well-defined lytic regions with bone expansion in early phase

      • “Cotton wool” appearance later in lytic-sclerotic phase

      • On MRI, hypointense on T1 and heterogeneous enhancement

    • Aneurysm: cavernous or other ICA segments

      • Rounded “mass,” low signal/flow void on MRI: must recognize!

      • Pulsation artifact in phase encoding direction

      • CT or magnetic resonance (MR) angiography to confirm

    • Arachnoid granulation: lesions found along dural sinuses and dural surface, typically incidental but in patients with CSF leaks may represent the site of osteodural defect.

    • Basal cephalocele: uncommon, usually congenital

    • Persistent craniopharyngeal canal: developmental anomaly resulting in a persistent tract from nasopharynx to pituitary fossa.

      • Smoothly marginated midline canal between presphenoid and basisphenoid.

      • Typically incidental finding but may be associated with pituitary abnormalities, cephaloceles, midline craniofacial anomalies, or rarely even tumors arising from tissue within the canal.

    • Ecchordosis physaliphora: benign nodule of tissue in the dorsal clivus and/or prepontine cistern considered to represent ectopic notochordal remnant.

      • Benign clival variant of chordoma

      • Hyperintense on T2, but no enhancement (distinguishes from chordoma)

      • Often shows restricted diffusion

Perineural Tumor Spread

General

    • Spread of malignant tumor along sheath of large nerves

    • Most commonly along CN V and VII branches

    • Contiguous spread from the primary tumor site along nerve tracks via epineurium/perineurium distant from primary site, do not confuse with “perineural invasion” at site of primary tumor invasion on histopathology

    • Often retrograde but can also be antegrade

    • Important to identify for initial staging and management planning—carefully evaluate major nerve pathways according to primary tumor site

    • Some head and neck cancer types have particularly high propensity (e.g., adenoid cystic carcinoma [ACC]) but SCC is much more common therefore overall more commonly seen with SCC; can also be seen with desmoplastic melanoma and lymphoma

    • Subtle but may be seen on CT:

      • Asymmetry and soft tissue infiltration in PPF, neural foramina; widening of these structures when more advanced

    • Contrast-enhanced high resolution MRI is the optimal technique for evaluation of perineural spread of tumor.

    • May also see secondary findings: look for denervation changes

Differential Diagnosis (DDx)

    • Nerve sheath tumors

      • Tubular, fusiform, lobular mass along nerve or nerves

      • Typically larger than perineural tumor spread

      • No other primary head and neck tumor/malignancy

    • Skull base meningioma

      • Homogeneously enhancing dural-based mass

      • May extend into neural foramina, jugular foramen, or PPF

    • Invasive fungal sinusitis

      • Immunocompromised patients, including diabetics

      • Infiltrating disease but does not follow nerves exclusively

    • Sarcoidosis

      • Nerve involvement may mimic perineural tumor spread

      • Absence of primary head and neck malignancy

      • May have other associated findings such as dural-based inflammation, leptomeningeal component

Orbit

General

Orbital Spaces ( Figs. 7.11 7.12 )

    • Intraconal space: space inside the rectus muscle pyramid

      FIG. 7.11

      FIG. 7.12

    • Extraconal space: space outside the rectus muscle pyramid

    • Preseptal space

    • Postseptal space

    • Lacrimal fossa

Orbital Structures

    • Globe (anterior chamber, posterior chamber, lens, vitreous, sclera/choroid/retina)

    • Intraconal, extraconal fat

    • Optic nerve and sheath

    • Ophthalmic artery and vein

    • Rectus muscles

Orbital Septum

    • Fascia arising from orbital rim periosteum

    • Attaches to outer margins of bony orbit and deep tissues of lids

    • Separates structures in the orbit from soft tissues in the face (postseptal vs. preseptal)

Globe

Retinoblastoma

    • Malignant tumor that arises from neuroectodermal cells of retina. Clinical: leukokoria (white mass behind pupil). Age: <3 years (70%)

    • 30% bilateral, may also be multifocal within one eye

    • 60% sporadic, 40% hereditary, 10% of patients have a positive family history

Radiographic Features

    • Intraocular mass

    • High density (calcification, hemorrhage)

    • Dense vitreous, common (secondary to hemorrhage)

    • Calcifications ( Fig. 7.13 ) are common (90%); in absence of calcifications suspect other mass lesions:

      • Persistent hyperplastic primary vitreous (PHPV)

      • Retrolental fibroplasia (retinopathy of prematurity); calcium may be seen if advanced

      • Toxocariasis (no calcification acutely)

      • Coats disease

      FIG. 7.13

    • MRI findings:

      • T1: variable, mildly hyperintense compared with vitreous (unless hemorrhage in vitreous)

      • T2: hypointense relative to vitreous

      • T1 postcontrast: moderate to marked heterogeneous enhancement

    • Primary role of imaging is to determine tumor spread:

      • Scleral breakthrough

      • Optic nerve extension

      • Intracranial spread

Pearls

    • Tumors may occur bilaterally or trilaterally (bilateral + intracranial, pineal region tumor much more common than suprasellar)

    • Associated with other malignancies (osteosarcoma most common) later in life; also, risk of postradiation sarcoma in treatment field

Melanoma

    • Most common (75%) primary ocular malignancy in adults. Arises from pigmented choroidal layer; retinal detachment is common.

Radiographic Features ( Fig. 7.14 )

    • Thickening or irregularity of choroid (localized, polypoid, or flat)

      FIG. 7.14

    • Exophytic, biconvex mass lesion

    • Usually unilateral, posterior location

    • Retinal detachment, common

    • Contrast enhancement

    • MRI: T1W hyperintense, T2W hypointense (can vary based on pigmentation)

    • Poor prognostic indicators:

      • Large tumor size

      • Lack of pigmentation associated with aggressiveness

      • Infiltration of the angles, optic nerve, sclera, ciliary body

Persistent Hyperplastic Primary Vitreous (PHPV) ( Fig. 7.15 )

Caused by persistence of portions of the fetal hyaloid artery and primary vitreous in Cloquet canal. Associated with ocular dysplasias (e.g., Norrie disease = PHPV, seizures, deafness, low intelligence quotient [IQ]). Clinical findings of blindness, leukokoria, and microphthalmia. Unilateral more common. Rare.

FIG. 7.15

Radiographic Features

    • Small globe (microphthalmia)

    • Vitreous body hyperdensity along the remnant of the hyaloid artery

    • No calcification rare (in contrast to retinoblastoma)

    • Complications:

      • Retinal detachment

      • Chronic retinal hemorrhage

Retrolental Fibroplasia (Retinopathy of Prematurity)

Toxic retinopathy caused by oxygen treatment (e.g., for hyaline membrane disease [HMD]). A retinal vasoconstriction leads to neovascularization and fibrovascular proliferation of the posterior vitreous and retina. Typically bilateral, retinal detachment common, may have associated hemorrhage, calcification rare except in advanced stages.

Coats Disease

Primary vascular abnormality (exudative retinopathy) causing lipoprotein accumulation in retina, telangiectasia, neovascularization, and retinal detachment (pseudoglioma). Age: typically first decade, male predominance. Rare.

Radiographic Features

    • Unilateral (90%)

    • Retinal detachment (V-shaped contour)

    • Dense vitreous/subretinal exudates

    • Calcification uncommon

    • Hyperintense (T1 and T2) proteinaceous, hemorrhagic exudate

    • Nerve enhancement in advanced disease as a result of secondary glaucoma

Drusen

Focal calcification in hyaline bodies in the optic nerve head. Usually bilateral and asymptomatic but may be associated with macular degeneration. Blurred disk margins may be mistaken for papilledema. On CT, seen as punctate hyperdensity most commonly at optic nerve head or macula.

Globe-Shape Abnormalities ( Fig. 7.16 )

    • Coloboma: focal outpouching involving retina, choroid, iris; caused by deficient closure of fetal optic fissure; located in region of optic disc. Associated with various congenital globe, CNS, and other systemic anomalies.

      FIG. 7.16

    • Staphyloma: acquired defect of globe wall with thinning of posterior sclera-uveal rim and protrusion of choroid or sclera. On imaging, see elongated globe with focal deformity, usually posterior, but not as pronounced as coloboma.

    • Axial myopia: anteroposterior (AP) elongation but no protrusion

    • Buphthalmos: congenital glaucoma, anterior ocular chamber drainage problem.

    • Enlarged globe, increased depth of anterior chamber.

Leukokoria

Leukokoria refers to a white pupil. Clinical, not a radiologic, finding. Underlying causes:

    • Retinoblastoma

    • PHPV

    • Congenital cataract

    • Toxocariasis

    • Other

      • Sclerosing endophthalmitis

      • Coats disease

      • Retrolental fibroplasia

      • Trauma

      • Chronic retinal detachment

Retinal Detachment ( Fig. 7.17 )

Separation of the sensory retina from the outer pigmented epithelium. Appears in a characteristic V shape, with the apex of the detachment at the optic disc. The presence of retinal or choroidal detachment may be caused by an ocular mass.

FIG. 7.17

Choroidal Detachment (see Fig. 7.17 )

Usually results after ocular surgery, trauma, or uveitis, causing fluid to accumulate in the choroidal space. Characteristic appearance spares the posterior third of the globe (region of the optic disc) in contradistinction with retinal detachment.

Optic Nerve

Optic Nerve Glioma

Most common cause of diffuse optic nerve enlargement, especially in childhood. Pathology: childhood lesions most commonly low grade astrocytomas (grade I pilocytic astrocytoma > grade II fibrillary astrocytoma). In patients with neurofibromatosis type 1 (NF1), pathology may be perineural arachnoid gliomatosis (PAG) rather than true astrocytoma. In adults, commonly high-grade astrocytomas. Clinical findings include loss of vision, proptosis (bulky tumors). Most common in first decade of life. In NF1 the disease may be bilateral.

Radiographic Features

    • Types of tumor growth: tubular, excrescent, fusiform widening of optic nerve

    • Enlargement of optical canal; >1 mm difference between left and right is abnormal.

    • Lower CT density than meningioma

    • Contrast enhancement variable

    • Calcifications rare (but common in meningioma)

    • Tumor extension best detected by MRI: chiasm → optic tracts → lateral geniculate body → optic radiation

Optic Nerve Meningioma

Optic nerve sheath meningiomas arise from arachnoid rests in meninges covering the optic nerve. Age: fourth and fifth decades (female predominance in adults); younger patients typically have neurofibromatosis type 2 (NF2). Progressive loss of vision.

Radiographic Features

    • Mass

      • Tubular, 65%

      • Eccentric (exophytic), 25%

      • Fusiform, surrounding the optic nerve, 10%

      • Calcification (common)

    • Enhancement

      • Intense contrast enhancement

      • Linear bands of enhancement (nerve within tumor): “tramtrack sign”

    • Other

      • Sphenoid bone and/or optical canal hyperostosis in advanced tumors

Optic Neuritis

Clinical Findings

    • Visual loss

    • Pain on eye movement

    • Afferent papillary defects

Causes

    • Isolated (idiopathic)

    • Multiple sclerosis (MS)

    • Neuromyelitis optica (Devic syndrome)

    • Acute demyelinating encephalomyelitis (ADEM)

    • Pediatric optic neuritis: rare, may follow viral illness or vaccination, ADEM

    • 40%–60% of patients ultimately develop MS (and 70%–90% of MS patients develop optic neuritis at some point)

Radiographic Features (Acute Phase)

    • Coronal T2W or postgadolinium T1W with fat suppression best for diagnosis

    • T2W: obliteration of the perioptic space; increased T2 signal of the affected optic nerve

    • Enhancement of the optic nerve

Extraocular Tumors and Vascular Lesions

Vascular Lesions

    • Orbital cavernous venous malformation (previously/commonly known as cavernous hemangioma ): adults, not a true neoplasm, rather vascular malformation; true capsule, benign, most common vascular orbital mass in adults

      • Most commonly in lateral intraconal space

      • Well-defined nonaggressive mass

      • Hyperintense on T2W images

      • Progressive enhancement “fill-in”

    • Orbital infantile hemangioma (capillary hemangioma): benign vascular tumor of infancy, no capsule

      • Lobular or infiltrative hypervascular, intensely enhancing mass

      • On T2W images: hyperintense, flow voids may be visible.

      • Most frequently superficial extraconal location, may have postseptal extension, uncommonly presents as exclusively retrobulbar mass

      • Grows for <1 year and then typically involutes

    • Venous, lymphatic, or venolymphatic malformations: vascular malformation with or without lymphatic component

      • Multiloculated, transspatial lesions

      • Those with significant lymphatic component tend to be more cystic and have propensity to hemorrhage with fluid-fluid levels.

      • Those with predominantly venous component tend to have more homogenous enhancement.

    • Venous varix: distensible venous channel with systemic connection

      • Dynamic enlargement of lesion with provocative maneuver (e.g., Valsalva)

      • May not be visible when patient relaxed

      • May present with thrombosis or hemorrhage

    • Hemangiopericytoma: uncommon, slow-growing vascular neoplasm that can be benign or malignant

      • Well-circumscribed or invasive when high grade

      • May remodel or erode bone

      • Avidly enhancing

      • Flow voids common on T2W images

    • Other vascular lesions: AVM, dural arteriovenous fistula, and cavernous carotid fistula

Dermoid Cyst

Common orbital tumor in childhood. Age: typically present in the first two decades.

Radiographic Features

    • Low CT attenuation and T1 hyperintensity (fat) are diagnostic.

    • Contiguous bone scalloping or sclerosis is common.

    • May contain debris (inhomogeneous MRI signal).

    • Calcification present occasionally.

Lacrimal Gland Tumors

    • Lymphoid

      • Benign reactive lymphoid hyperplasia

      • Lymphoma

    • Epithelial tumors

      • Benign mixed (pleomorphic) tumor (most common epithelial tumor)

      • ACC

      • Mucoepidermoid CA

      • Malignant mixed tumor (carcinoma ex pleomorphic adenoma)

Rhabdomyosarcoma

Most common malignant orbital tumor in childhood. Mean age: 7 years.

Radiographic Features

    • Large, aggressive soft tissue mass (intraconal or extraconal)

    • Metastases to lung and cervical nodes

Metastases

Adults: breast, lung, renal cell, prostate CA, melanoma. Breast metastasis to the orbit may have retractile fibrotic stroma and paradoxically be associated with enophthalmos. There can also be direct extension of malignant sinonasal tumors to the orbit. Children: rare, neuroblastoma, leukemia.

Infectious, Inflammatory, and Infiltrative Lesions

Orbital Infection

The orbital septum represents a barrier to infectious spread from anterior to posterior structures. Common causes of orbital infection include spread from infected sinus and less commonly trauma.

Radiographic Features

    • Periorbital cellulitis: soft tissue swelling

    • Postseptal infection (true orbital cellulitis)

      • Infiltration of extraconal, postseptal fat

      • Subperiosteal infiltrate or abscess

      • Lateral displacement of enlarged medial rectus muscle

      • Stranding of retrobulbar fat if intraconal extension

      • Proptosis

    • Evaluate paranasal sinuses for potential source

    • Bacterial infections can be complicated by cavernous sinus thrombosis.

Thyroid Ophthalmopathy

Orbital pathology (cellular infiltration, deposition of glycoproteins and mucopolysaccharides in the orbit, fibrosis) caused by autoantibodies targeting thyrotropin receptors found in orbit (in addition to thyroid). Clinical: painless proptosis; patients may be euthyroid, hypothyroid, or hyperthyroid. Functional classification (clinical severity and risk):

    • Mild: eyelid lag and retraction with proptosis in setting of active hyperthyroidism

    • Moderate: soft tissue inflammation and intermittent myopathy; stabilizes without major sequelae

    • Severe: rapid and fulminant, greater mass effect, severe sequelae including optic nerve compromise

Treatment: prednisone → radiation therapy → surgical decompression; surgery or 131 iodine (I) for thyroid.

Radiographic Features ( Figs. 7.18 7.19 )

    • Exophthalmos

      FIG. 7.18

      FIG. 7.19

    • Muscle involvement

    • Mnemonic for involvement: I'M SLow :

      • I nferior (most common)

      • M edial

      • S uperior

      • L ateral

    • Enlargement is maximal in the middle of the muscle and tapers toward the end (infiltrative, not inflammatory disease).

    • Spares tendon insertions (although may be involved in acute phase)

    • Often bilateral, symmetric

    • Other

      • Straightened or stretched optic nerve

      • Expansion of orbital fat

      • Lacrimal gland enlargement

Idiopathic Orbital Inflammation (Orbital Pseudotumor)

Inflammation of orbital soft tissues of unknown origin

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here