Temporal Bone Flashcards
pathology of external ear
EAC atresia, SCC, swimmer’s ear (acute external otitis), surfer’s ear (EAC exostosis), malignant otitis externa, acute external otitis, first branchial cleft cyst, keratosis obturans
pathology of middle ear
hypoplasia of ossicles, cholesteatoma, otitis media, mastoiditis, glomus tympanicum, aberrant ICA, dehiscent jugular bulb, oval window atresia, facial nerve schwannoma
pathology of inner ear
cochlear dysplasia, superior semicircular canal dehiscense, semicircular canal hypoplasia, enlarged vestibular aqueduct, otospongiosis/otosclerosis, Paget disease, fibrous dysplasia, labryrinthitis, petrous apicitis, cholesterol cyst
middle ear contents
tympanic membrane
ossicles (malleius/incus/stapes)
stapedius muscle
facial nerve
inner ear contents
cochlea, semicircular canals, vestibule, utricle, saccule, vestibular aqueduct, coclear aqueduct
congenital EAC stenosis, hypoplasia, atresia
malformations of external ear
typically inner ear not involved since it has different embryological origin
acute external otitis media
swimmers ear; bacterial infection of external ear since in high humidity
EAC exostosis
surfer’s ear; exostosis of EAC in those who swim/surf in cold waters
necrotizing external otitis
malignant otitis externa; seen in elderly diabetic/immunocompromised; Pseudomonas vs Aspergillus
extensive enhancement around external ear with associated bony erosion
Keratosis obturans
keratin plugs within an enlarged EAC; seen in young patients with sinusitis and bronchiectasis
usually bilateral
cholesteatoma
acquired cholestatoma, more common in middle ear
usually associated with bony erosion
white mass behind tympanic membrane; restricts diffusion
EAC malignancy
SCC–usually sun exposure or chronic inflammation
oval window separates?
air filled middle ear and fluid filled inner ear
glomus tympanicum
extra adrenal pheochromocytoma (paraganglioma) of the middle ear
associated with pulsatile tinnitus or conductive eharing loss
vascular red mass behind the tympanic membrane
facial nerve schwannoma
present with facial nerve palsy;
involve geniculate ganglion, followed by labryinthine and tympanic segments
facial nerve segments
labryinthine, tympanic, mastoid
labrinthine segment, tympanic membrane
IAC to geniculate ganglion; superior to cochlea
gives off greater suprficial petrosal nerve
tympanic segment tympanic membrane
horizontal; courses under lateral semicircular canal
mastoid segment tympanic membrane
descending; courses inferiorly then exits at the stylomastoid foramen
nerve to stapedius
chorda tympani
cholesterol granuloma
cholesterol cyst; petrous apex lesion that may occur in the middle ear
giant cell reaction to cholesterol crystals initially incited by an obstructed air cell
blue mass behind tympanic membrane
cholesteatoma, middle ear
non-neoplastic lesion of temporal bone; skin in the wrong place; white mass behind tympanic membrane
persistent fetal epithelial squamous cell nests, or due to sequela of tympanic membrane perforation, inflammation, trauma
more common in younger individuals (EAC cholesteatomas in older/middle aged)
cochlear dysplasia
mondini deformity
incomplete development of cochlea resulting in confluence of apical/middle turns; intact basilar turn
incomplete partition type II
michel aplasia
complete lack of development of inner ear
enlarged vestibular aqueduct syndrome
may lead to progressive hearing loss while playing contact sports
vestibular aqueduct should not be larger than posterior semicircular canal; often seen at same level in axial plane
otospongiosis
otosclerosis; bone dysplasia of otic capsule seen in young/middle aged women; bilateral usually
types fenestral and retrofenestral
retrofenestral and fenestral otospongiosis
fenestral: more common; fissula ante fenestrum (anterior to oval window)
retrofenestral (cochlear): severe form; involve otic capsule and lateral wall of labryinth
ddx of cochlear demineralization
retrofenestral otospongiosis, osteogenesis imperfecta, fibrous dysplasia, paget disease (based on age)
labryinthitis
inflammation of inner ear: infectious/autoimmune
3 stages: acute > fibrous > labrytinthitis ossificans
acute labyrinthitis
pus in inner ear; enhancement of inner ear
may also look like cochlear/intralabyrinthine schwannoma
fibrous labyrinthitis
endolymph/perilymph replaced with fibrous strands
mild/decreased post-contrast enhancement
labryinthitis ossificans
final stage of labyrinthitis
calcified debri where normal endolymph and perilymph is seen
best evaluated on CT for calcifications; decreased signal on T2 weighted MRI
types of temporal bone fractures
longitudinal and transverse based on axis of temporal bone
longitudinal temporal bone fracture
most common; aligned with axis of petrous portion of temporal bone
responsible for conductive hearing loss
may involve ossicles and facial nerve; risk for development of subsequent acquired cholesteatoma if tympanic membrane disrupted
transverse temporal bone fracture
perpendicular to long axis of petrous portion of temporal bone
sensorineural hearing loss; involve bony labrinth
petrous apex anatomy
medial portion of the temporal bone
borders surahyoid neck and intracranial compartment; contains Dorello’s canal (CN VI), Meckel’s cave (trigeminal ganglion), and petrous portion of ICA
cholesterol cyst
foreign body giant cell reaction to cholesterol crystals; expansile mass with internal hemorrhage and fluid that does not suppress on fat suppression
apical petrositis/petrous apicitis
rare complication of infectious otomastoiditis; infection extends into pneumatized petrous apex
Gradenido triad
otomastoiditis, facial pain from trigeminal neuropathy at Meckel’s cave, lateral rectus palsy from CN 6 palsy at Dorello’s canal
vascular complications include thrombosis of ICA and dural veins
petrous apex schwannoma
CN V, VII, VIII
smoothly expansile enhanscing mass with bony remodeling; may become cystic or contain fluid levels
lancherhans cell histiocytosis/eosinophilic granuloma
neoplastic proliferation of eosinophils and langerhans cells
most common site of skull base involvement
destructive lesion with nonsclerotic margins
chondrosarcoma
malignant neoplasm arises from midline clivus or off midline petroclival synchondrosis
ring-and-arc chondroid matrix; lobular cauliflower T2 weighted images
chordoma
usually from clivus; may expand laterally to involve petrous apex
Petrous apex lesions DDX
ACGMES MC
apical petrositis, congenital cholesteatoma, cholesteral granuloma, meningioma, eosinophilic granuloma, schwannoma,
mets/myeloma, chondrosarcoma/chordoma
