Imaging Techniques

Coronal plane

Anterior plane - Anterior cochlea, geniculate ganglion, & malleus

Middle plane - Oval window, vestibule, & IAC (also EAC & tympanic cavity)

Posterior plane - Semicircular canals & mastoid

Axial plane

Lower level - External auditory canal & cochlea (basal turn) ossicles

Middle level - Cochlea (middle & apical turns), ossicles, vestibule, & IAC

Upper level - Semicircular canals & vestibular aqueduct

Embryology

External & middle ear - 1st & 2nd branchial arches & intervening groove (cleft)

Meckel's cartilage (1st arch) forms most of malleus & part of the incus

Reichert's cartilage (2nd arch) forms stapes, including footplate, & facial nerve canal

Inner ear - Otic capsule

Trauma

Clinical

Requires major trauma to fracture the temporal bones

Hearing loss, vertigo, CSF leak, 7th nerve paralysis

Longitudinal fractures - most common (classically >80% but many are mixed)

Pass through mastoid or EAC

All go through middle ear with high incidence of ossicular derangement (Incus & incudostapedial joint most common) and conductive hearing loss

Inner ear usually spared

Facial paralysis in about 15% (proximal tympanic segment just distal to

geniculate ganglion)

CSF leak (usually caused by fracture through tegmen or the mastoid)

- Otorrhea: perforation or tear of tympanic membrane

- Rhinorrhea: tympanic membrane intact

Injury to carotid artery, jugular vein or sigmoid sinus

Transverse fractures

Commonly involve the labyrinth

- Cochlear fracture: sensorineural hearing loss, permanent if cochlear

nerve transected

- Labyrinthine fracture: severe vertigo

Facial palsy in 50% - permanent if 7th nerve transected (usually the distal labyrinthine segment just proximal to geniculate ganglion)

Perilymph fistula (can also result from barotrauma)

- Disruption of stapes footplate, oval window or round window

- Pneumolabyrinth highly suggestive but not always present

- Labyrinthine enhancement sometimes present

Injury to carotid artery

Diseases of the External Ear

Inflammatory disease

Malignant external otitis

- Pseudomonas common in diabetic patients

- Can extend to skull base

Tumors of the external auditory canal

Squamous cell carcinoma

Adenocarcinoma (ceruminoma)

Diseases of the Middle ear and Mastoid

Acute otomastoiditis - an acute bacterial infection. Complications include:

Coalescence - erosion of bony septa with osteomyelitis

Subperiosteal abscess over mastoid

Labyrinthitis

Petrous apicitis

Sigmoid sinus thrombosis

Intracranial empyema, meningitis or cerebral abscess

Chronic otomastoiditis - caused by dysfunction of the eustachian tube.

Middle ear effusion

Tympanic membrane retraction

Inflammatory granulation tissue & cholesterol granuloma (hemorrhagic cysts secondary to foreign body reaction to cholesterol crystals; lined by fibrous connective tissue)

Acquired cholesteatoma

Associated with chronic otomastoiditis

Lined by keratinized stratified

squamous epithelium

Results from pars flaccida retraction & ingrowth of epithelium into trapped pockets with extension into Prussak's space

Cholesteatomas arising from the region of the pars tensa extend into the posterior tympanic cavity and involve the sinus tympani and the facial recess.

Tympanosclerosis - post-inflammatory

fixation of the ossicles with conductive hearing loss

Surgical procedures

Simple mastoidectomy - limited removal of mastoid air cells

Modified mastoidectomy - removal of external auditory canal wall along with mastoid air cells, but preserving the ossicles

Radical mastoidectomy - removal of EAC wall, mastoid air cells and the ossicles, but attempted preservation of the stapes superstructure

Prosthetic stapedectomy - Prosthetic materials include stainless steel wire, metallic piston, Teflon, Silastic or plastic

Tympanoplasty - Plastic procedures to cover perforations in tympanic membrane

Ossiculoplasty

Paraganglioma

Glomus tympanicum - arise from paraganglia along the tympanic branch of the glossopharyngeal nerve (Jacobson's nerve) within the middle ear cavity

Glomus jugulare - arise from paraganglia along the auricular branch of the vagus nerve (nerve of Arnold) in the jugular fossa

Patients present with pulsatile tinnitus, conductive hearing loss, retrotympanic mass, and cranial nerve deficits

Most tumors are slow growing but locally invasive

Differential diagnosis

- High & exposed jugular bulb

- Aberrant carotid artery

- Schwannoma

- Primary & metastatic bone tumors

- Other middle ear tumors,

cholesteatoma, squamous cell carcinoma

Diseases of the Inner Ear

Labyrinthitis

Inflammation of the membranous labyrinth

Patients present with sensorineural hearing loss and vertigo

Most commonly viral, but bacterial, autoimmune, luetic or tuberculous also possible

Source can be tympanic, meningeal, hematogenous, posttraumatic or postsurgical

Otosclerosis

Acute phase: otospongiosis - resorption of bone

Chronic phase: otosclerosis - sclerosis of bone

65% females & 80% of cases are bilateral

Onset during the 2nd and 3rd decades

Fenestral otosclerosis (most common)

- Conductive hearing loss

- Fixation of the footplate of the stapes at oval window

- Surgical correction possible

Retrofenestral (cochlear) otosclerosis (otospongiosis)

- Sensorineural hearing loss

- Cochlear implantation does not work

Acoustic schwannoma

Can be intracanalicular, in the CP angle or intralabyrinthine (rare)

Patients present with sensorineural hearing loss, tinnitus, & disequilibrium

Arise from the nerve sheath of the vestibular division of 8th nerve

Benign, slowly growing, encapsulated neoplasm

Differential diagnosis

- Meningioma

- Epidermoid

- Other cranial nerve schwannomas

- Aneurysm

- Paraganglioma

- Primary or metastatic bone

tumor

Endolymphatic sac tumors

Rare, locally invasive papillary cystadenomatous tumors

Diseases of the Petrous Apex

Cholesterol granuloma (cyst)

Chronic inflammatory cysts containing blood products & cholesterol crystals

Cyst capsule lined by fibrous tissue

Hyperintense on T1 & T2-weighted images

Primary cholesteatoma

Arise from epithelial rests within the petrous bone

Capsule lined by stratified squamous epithelial; cyst contents are primarily desquamated keratin

CT and MR appearance similar to cholesterol granuloma

Petrous apicitis (Gradenigo's syndrome)

Otomastoiditis, 6th nerve palsy, pain in distribution of 5th nerve

Intrapetrous carotid artery aneurysm

Rare lesions

Characteristic appearance on MR, with heterogeneous texture due to thrombus of different ages & variable signal loss from complex flow within patent lumen of the aneurysm

Chondrosarcoma

Rare lesions arising from embryonal rests at sutural sites

CT features - heterogeneous with calcifications

MR features - most are markedly hyperintense & heterogeneous on T2W images & with heterogeneous enhancement

Facial Nerve Pathology

Inflammatory disease

Bell's palsy

- Idiopathic but usually follows a viral infection

- Usually self-limited

Ramsey Hunt syndrome - herpes zoster oticus

Lyme disease

Syphilis

Imaging - gadolinium enhancement of the 7th nerve

CAUTION: The geniculate ganglion & post-ganglionic nerve segment normally exhibit mild enhancement. Also, the stylomastoid canal contains a vascular plexus that enhances.

Facial nerve tumors

Schwannoma - can occur anywhere along the intrapetrous course of the 7th nerve but the region of the geniculate ganglion is most common (< 1/2 present with a 7th nerve palsy)

Hemangioma - capillary or cavernous types

Differential diagnosis

- Epidermoid tumor

- Acquired cholesteatoma

- Tympanic segment: glomus tympanicum, persistent stapedial artery, cholesteatoma

- Stylomastoid segment: glomus jugulare, parotid adenoid cystic CA

Congenital Anomalies

General principles - External & middle ear anomalies often associated with facial,

cervical & skeletal dysplasias. Patients present with external ear deformities and a conductive hearing loss. Inner ear anomalies are often isolated. Patients present with a sensorineural hearing loss.

More common anomalies of the external

& middle ear

Atresia/stenosis of the EAC (tympanic ring dysplasia/aplasia) - atresia plate with fusion of neck of malleus to plate & variable development of ossicles and middle ear cavity.

First (mandibular) branchial arch dysplasia - maldevelopment of the malleus, incus& mandible

Second (hyoid) branchial arch dysplasia - maldevelopment of the stapes and footplate, styloid process and superior cornu of the hyoid bone; also anterior migration of the facial nerve canal within the petrous bone.

Inner ear anomalies

Semicircular canals & vestibule - Lateral SSC invariably involved. The SSC's appear short and wide or form common lumen with vestibule.

Cochlear anomalies

Labyrinthine aplasia (Michel's deformity) - single small cystic cavity. Milder forms also occur (Cochlear aplasia/hypoplasia)

Incomplete partition (Mondini malformation) - most common inner ear anomaly. Cochlea consists of a basilar turn with a cystic cavity. Atretic or dilated vestibular aqueduct.

Perilymphatic hydrops - refers to increased pressure in the inner ear; caused by communication between the subarachnoid space and inner ear; can lead to perforation of the stapes footplate and a CSF leak and possibly meningitis.

Etiology:

- trauma most common

- defective development of the lamina cribrosa

- congenitally wide cochlear aqueduct with communication of CSF with perilymph

Endolymphatic hydrops

Symptoms: sensorineural hearing loss and vertigo

Source: can be congenital, acquired, or idiopathic

Cause: deficient absorption of endolymph

Imaging: dilated endolymphatic sac and vestibular aqueduct

Meniere's disease: idiopathic but some evidence for viral etiology

Superior Canal Dehiscence Syndrome

Cause: dehiscence of bone overlying the superior semicircular canal

Symptoms: vertigo & oscillopsia with sound or pressure stimuli

Imaging: diagnosed with thin-section coronal CT

Treatment: surgical plugging of the SSC

Vascular anomalies

Aberrant carotid

Persistent stapedial artery

High or dehiscent jugular bulb

References

Som PM, Curtain HD, eds., Head and Neck Imaging, Mosby, St. Louis, 1996, Chapters 26-33, pp. 1300-1549.

Harnsberger HR, Hudgins PA, Wiggins RH, Davidson HC: Diagnostic Imaging – Head and Neck. 1st ed., Saunders, Philadelphia, 2005.

Hesselink JR, Remley KB: Skull base and temporal bone, in Edelman, Hesselink, Zlatkin & Crues, eds., Clinical Magnetic Resonance Imaging, 3rd edition, Saunders-Elsevier, Philadelphia, 2006, pp 1970-2029.

Davidson HC: Imaging of the temporal bone. MRI Clinics North Am 10:573-613, 2002.