Clinical Embryology and Anatomy of the Inner Ear and Related Structures

Vocabulary flashcards covering inner ear embryology, anatomy of the membranous labyrinth, and relations of the middle and inner ear walls, skull base canals, and cranial nerves.

Membranous labyrinth

A closed sac-like structure filled with endolymph that contains sensory end organs of hearing and balance.

Bony labyrinth

The outer bony cavity containing perilymph that has openings connecting the inner ear to the middle ear and brain.

Otic placode

A specialized area of surface ectoderm overlying the hindbrain that invaginates through an otic pit to become an otic vesicle, developing into the membranous labyrinth.

Utricle

A part of the membranous labyrinth into which the $3$ semicircular canals open through $5$ openings.

Crus commune

The common opening between the superior semicircular canal and posterior semicircular canal that leads into the utricle.

Endolymphatic Sac

A structure formed from the ducts of the saccule and utricle that absorbs endolymph.

Ductus reuniens

The duct that connects the saccule to the scala media (cochlear duct).

Stylomastoid Foramen

An opening present between the styloid process and mastoid through which CN VII exits; involvement causes facial nerve palsy.

Jugular Bulb

A vascular structure lying in the floor of the middle ear through which tumors of the jugular bulb can project.

High Resolution CT scan (HRCT)

The best investigation for conditions of the middle ear and temporal bone fractures.

Internal Carotid Artery (ICA)

An artery related to the anterior wall of the middle inner ear that runs horizontally as the petrous part inside the carotid canal before entering the cavernous sinus as the cavernous part.

Tegmen Tympani

The roof of the middle ear separating it from the middle cranial fossa (temporal lobe); infection spreading here leads to a temporal lobe abscess.

Arcuate Eminence

A bulge in the roof of the inner ear produced by the Superior Semicircular Canal (SSC).

SSC dehiscence

A condition where the bone over the Superior Semicircular Canal is thin or gaping, allowing a rise in intra-cranial pressure to stimulate the inner ear and result in inner ear symptoms.

Meckel's Cave

A depression containing the Gasserian ganglion (ganglion of CN V) where CN V gives off ophthalmic, maxillary, and mandibular branches; involvement of CN V causes retro-orbital pain with ear symptoms.

Dorello's Canal

A canal present at the petrous apex through which CN VI passes; petrositis here causes ear complaints and diplopia.

Internal Acoustic meatus (IAM)

A canal connecting the inner ear to the posterior cranial fossa through which CN VII and CN VIII pass, and through which acoustic neuroma spreads intracranially.

Acoustic neuroma

A tumor that spreads intracranially through the Internal Acoustic meatus (IAM), with upper pole involvement affecting CN V and VI, and lower pole involvement affecting CN IX, X, and XI.

Jugular Foramen

An opening at the junction of the petrous and occipital bone through which CN IX, CN X, and CN XI pass to the floor of the middle ear.

Sigmoid Sinus

A sinus forming the posterior boundary of the mastoid that drains into the jugular bulb and Internal Jugular Vein (IJV); infection can spread here causing sigmoid sinus thrombosis and IJV thrombosis.