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MIDDLE EAR CLEFT

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Middle ear together with Eustachian tube, Aditus,Antrum, Mastoid air cells middle ear cleft.

Development Eustachian tube, tympanic cavity, attic, aditus, antrum

and mastoid air cells develop from endoderm of tubo -tympanic recess.

Malleus and incus mesoderm of first pharyngeal arch. Stapes second arch

Foot plate otic capsule.

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Middle ear

Mesotympanum ( opposite pars tensa)

Epitympanum (medial to shrapnellsmembrane)

Hypotympanum (below pars tensa)

Protympanum ( near tympanic orifice ofeustachian tube)

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Middle ear six sided box

Roof

Floor

Anterior wall

Posterior wall

Medial wall

Lateral wall

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Roof

Thin plate of boneTegmen tympani.

Separates tympanic cavity from middle cranialfossa.

Floor Thin plate of bone separates from jugular

bulb.

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Anterior wall

Separated form internal carotid artery , withopening of Eustachian tube, and canal for tensor

tympani.

Posterior wall

Close to mastoid air cells Bony projection pyramid ,with tendon of

stapedius.

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Aditus

Opening through which Attic communicates withAntrum & lies above the pyramid.

Facial recess

Depression in posterior wall lateral to pyramid.

Medially vertical part of 7

th

nerve Laterally chorda tympani

Above fossa incudis

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Medial wall

Formed by labriynth

A Bulge promontory due to basal coil ofcochlea.

Oval window fixed with foot plate of stapes.

Round window or Fenestra cochlea coveredby secondary tympanic membrane.

Canal for facial nerve above the oval window.

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Above the canal for facial nerve prominence

of lateral semi circular canal.

Anterior to oval window hook like projection

processus cochleariformis.

Marks the level of genu of facial nerve.

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Lateral wall

By tympanic membrane &

Bony outer attic wall scutum.

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Mastoid antrum

Large air containing space in the upper part

mastoid & communicates with the attic through

the aditus.

Roof- tegmen antri

Marked externally Mac Ewens triangle.

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Aditus-ad-Antrum :

Opening through which attic communicateswith the antrum.

Bony prominence of horizontal canal

medially.

Fossa incudis laterally

Facial nerve courses just below the aditus.

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Mastoid air cell system --

Bony cortex with honey comb of air cells .

Types of mastoid air cells :

Well pneumatised / cellular (well developed air

cells) Diploetic ( few air cells)

Sclerotic ( no air cells)

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Depending on the location ( mastoid air cells)

Zygomatic cells ( root of zygoma)

Tegmen cells( tegmen tympani)

Perisinus cells (over the sinus plate)

Retrofacial cells ( around the facial nerve)

Perilabryinthine cells ( above , below, behind thelabryinth)

Peritubal cells ( around eustachian tube)

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tip cells ( tip of mastoid)

Marginal cells.

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Blood supply of middle ear

Supplied by six arteries of which :

Anterior tympanic branch of maxillary arteryto the tympanic membrane.

Stylomastoid branch of posterior auricular

artery middle ear and mastoid air cells.

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