Anatomy

1. What 5 parts make up the temporal bone?
   Answer: Squamous, mastoid, petrous, tympanic and styloid process.

2. What are the 6 segments of the 7th cranial nerve?
   Answer: Cisternal (intra-cranial), intra-canalicular (internal auditory canal), labyrinthine segment, tympanic segment, mastoid segment and extra-cranial segment (parotid).

3. Does the otic capsule contain enchondral bone? True or False?
   Answer: True. The otic capsule is made up enchondral, endosteal and periosteal bone.

4. What are the two muscles of the tympanic cavity?
   Answer: The tensor tympani and stapedius muscles. The tensor tympani muscle inserts onto the neck of the malleus and is innervated by V3 (mandibular branch). The stapedius muscle inserts into the posterior surface of the neck of the stapes and is innervated by a branch of the facial nerve. Both muscles act to dampen sound transmission and thus protect the inner ear.

5. What structures make up the membranous (endolymphatic) labyrinth?
   Answer: The utricle, saccule, semi-circular ducts, cochlear duct (scala media) and endolymphatic duct and sac. The inner ear is made up of a membranous (endolymphatic) labyrinth containing the functional sensory epithelium surrounded by a bony labyrinth with an interposed perilymphatic labyrinth. The bony labyrinth is the bony shell that surrounds the membranous labyrinth and is made up of the vestibule, semicircular canals, and vestibular aquaduct.

Congenital

1. What embryologic structure does the inner ear develop from?
   Answer: The otic placode from ectoderm. The inner ear begins to develop in the third gestational week and arises from the otic placode. The otic placode originates from surface neuroectoderm located between the first branchial groove and hindbrain. Each placode invaginates into the mesenchyme forming the otic pit, and then the edges fuse to form the otic vesicle (otocyst).

2. Which branchial arches form the ossicles?
   Answer: The first branchial arch forms the bodies of the malleus and incus. The second branchial arch forms the crura of the stapes, the lenticular process and long crus of the incus, and the manubrium of the malleus. The footplate of the stapes originates from the otic capsule.

3. What features make up the Mondini malformation of the cochlea?
   Answer: A cochlea with 1.5 turns (the middle and apical coalesce to form a cystic apex), dilated vestibule and a large vestibular aquaduct.

4. Absence of the semi-circular ducts is frequently associated with what congenital syndrome?
   Answer: CHARGE syndrome (colobomas, heart anomaly, choanal atresia, retardation, genital and ear anomalies)

5. What is the normal size of the vestibular aquaduct?
   Answer: The vestibular aquaduct diameter should not exceed 1.5 mm or not be larger than the width of the posterior semicircular canal.

Inflammatory

1. Name at least 5 complications related to acute otomastoiditis.
   Answer: Meningitis, parenchymal/extracerebral abscess, empyema, dural sinus thrombosis, venous infarction, labyrinthitis, labyrinthine fistula, facial nerve involvement, coalescent mastoiditis, Bezold's abscess, petrous apicitis, and otitic intracranial hypertension (otitic hydrocephalus).

2. Name at least 5 sequelae of chronic otomastoiditis.
   Answer: Tympanic membrane retraction, acquired cholesteatoma, tympanosclerosis, granulation tissue, cholesterol granuloma, chronic OM with effusion, post-inflammatory ossicular fixation, non-cholesteatomatous ossicular erosion, and conductive hearing loss.

3. What are the 4 theories of acquired middle ear cholesteatomas?
   Answer: Retraction pocket, epithelial invasion through TM perforation, squamous metaplasia of middle ear epithelium, and basal cell hyperplasia.

4. Which acquired cholesteatoma is more common? Pars flaccida cholesteatoma or the pars tensa cholesteatoma?
   Answer: The pars flaccida cholesteatoma. The superior pars flaccida of the tympanic membrane lacks a middle fibrous layer and thus retracts more easily than the pars tensa. The pars flaccida cholesteatomas begin in Prussak’s space (lateral epitympanic recess) displacing the ossicles medially and often eroding the scutum and as it grows into the tegmen tympani. The mass also extends posteriorly in the epitympanum to the aditus ad antrum, extending into the antrum and mastoid air cells.

5. What are the three most common expansile masses to occur in the petrous apex?
   Answer: Cholesterol granuloma, cholesteatoma, and a mucocele. Cholesterol granulomas are a foreign body giant cell reaction to cholesterol deposits occurring in obstructed fluid-filled air cells developing a cycle of recurrent hemorrhage and granulation tissue. Cholesteatomas of the petrous apex can be primary or acquired. Mucoceles occurring in pneumatized petrous apex have similar pathophysiology to the paranasal sinuses as they both are lined with respiratory epithelium.

Trauma

1. Which temporal bone fracture pattern is more common in trauma, transverse or longitudinal fractures?
   Answer: Longitudinal fractures. Longitudinal fractures are parallel to the long axis of the petrous bone and make up 70-90% of temporal bone fractures. The less common transverse fracture runs perpendicular through the petrous bone and occurs about 20% of the time. However, oblique and mixed-type temporal bone fractures can also occur.

2. Is conductive hearing loss more common in longitudinal or transverse temporal bone fractures?
   Answer: Longitudinal type fractures. This type of fracture typically crosses the middle ear cavity and is often associated with ossicular dislocation.

3. What is the most common injury to occur to the ossicular chain?
   Answer: Incudostapedial subluxation. The incudostapedial joint is a very fragile enarthrosis and lies between two axes of rotation. The subluxation is thought to occur due to contraction of both the tensor tympani and stapedius muscles that results in a medial thrust of the incus and a posterior thrust of the stapes.

4. Facial nerve injury occurs more commonly with longitudinal or transverse temporal bone fractures?
   Answer: Facial nerve injury is more commonly seen in transverse fractures. Specifically, the most frequent site of injury to the facial nerve with transverse fractures involves the labyrinthine segment, and less commonly the geniculate ganglion and internal auditory canal.

5. Name at least 5 post-traumatic complications related to temporal bone fractures.
   Answer: Vertigo, hearing loss, facial nerve dysfunction, perilymphatic fistula, acquired cholesteatomas, CSF leak, meningitis, intracranial injuries and vascular injuries.

Tumors and tumor-like conditions

1. What is the most common extra-axial tumor to occur in the cerebellopontine angle?
   Answer: Vestibular Schwannoma. A Vestibular Schwannoma is a benign tumor of the nerve sheath composed of Schwann cells. The tumor is comprised of Antoni A and B type tissue, and can develop cysts or hemorrhage. Bilateral Vestibular Schwannomas are associated with NF-2.

2. Otosclerosis, also known as otospongiosis, resorbs which layer of the bony labyrinth?
   Answer: The middle endochondral layer. There is resorption of the endochondral layer of the bony labyrinth with replacement of spongy vascular bone. There are two categories: fenestral otosclerosis limited to the oval and round window niche and retro-fenestral otosclerosis involving primarily the cochlea. The disease is characterized by autosomal dominant inheritance with variable penetrance and expression. Otosclerosis more commonly affects women, presents with tinnitus and results in progressive hearing loss.

3. What are the three types of fibrous dysplasia (FD)?
   Answer: Pagetoid, sclerotic and cystic. Fibrous dysplasia is an inherited disorder characterized by gradual progressive replacement of normal bone by dysplastic fibroosseous tissue. There is failure to form normal mature lamellar bone due to defective osteoblastic activity resulting in immature woven bone mixed with fibrous tissue elements. A characteristic feature of FD results in bony expansion due to replacement of the normal medullary space, with variable imaging appearance depending on the FD type and ratio of fibrous to osseous elements.

4. What is the most common symptom of paragangliomas of the temporal bone?
   Answer: Pulsatile tinnitus. Paragangliomas result from chromaffin cells in paraganglia originating from embryonic neural crest cells, functioning as part of the sympathetic nervous system. These tumors are typically benign, but rarely can be malignant, and are hypervascular tumors that derive most of their blood supply from branches of the external carotid artery. The tumors are often named for the anatomic region they occur in, such as glomus tympanicum in the middle ear and glomus jugulare in the jugular foramen. Treatment includes surgery, embolization or radiation depending on the size and location of the tumors.

5. Endolymphatic sac tumors are non-destructive lesions of the middle ear cavity. True or False?
   Answer: False. Endolymphatic sac tumors (ELST) are rare slow growing papillary cystadenomas that generally appear histologically benign but are highly destructive and behave in an aggressive manner on imaging. ELST occur sporadically, but is also associated with Von Hippel-Lindau (VHL) disease. These tumors occur along the posterior petrous bone at the level of the vestibular aquaduct and on CT are characterized by permeative bone destruction with multiple bony spicules and can have intra-tumoral calcifications. On MR, these tumors show avid enhancement with signal voids representing vascular channels, demonstrate T1 hyperintensity due to recent hemorrhage and from elevated protein concentration resulting in a “salt and pepper” appearance.