Temporal Bone Anatomy

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ear surgery

Text of Temporal Bone Anatomy

Temporal Bone Anatomy

Anatomy Temporal bone Squamous portion Mastoid portion Petrous portion Tympanic portion Styloid process

External auditory canal Approximately 2.5-3.5 cm long 6-9 mm wide Outer 1/3 : extension of the cartilage of the auricle Inner 2/3 : incomplete ring of the tympanic bone Lined by skin

Tympanic membrane Separates the EAC from middle ear cavity Fibroelastic layer Outer surface : covered by canal skin Medial surface : by the middle ear mucosa The circumference of the membrane Thickened and forms annulus Open anterosuperiorly Pars flaccida Triangular segment, bordered by mallear fold Devoid of fibroelastic layer Pars tensa Convex medially : umbo

Middle ear Air-filled irregular space Boundary Lateral : TM, lateral attic wall Medial : capsule of the inner ear Superior : tegmen tympani Inferior : hypotympanic floor Three portions Mesotympanum Epitympanum Hypotympanum : covers the jugular bulb

Middle ear Pyramidal eminence In the posterior wall of of the mesotympanum Conical bony protrusion Stapedius m. & its tendon Facial recess Lateral to the pyramidal eminence Covers the upper portion of the mastoid segment of the facial canal Sinus tympani Medial to the pyramidal eminence Posterior pocket of mesotympanum

Tympanic membrane

Middle ear Ossicles Malleus, incus, stapes In the attic, head of malleus articulates with the incus body Malleus handle extends inferiorly to the TM The long process of the incus articulates with the head of stapes - Ice-cream appearance : head of malleus & incus body, short process

Ossicles

Posterior tympanum Pyramidal eminance sup inf, facial canal lat med Superolateral: facial sinus Inferolateral: lateral tympanic sinus Superomedial: posterior tympanic sinus

Ponticulus: pyramidal eminance promontory bony ridge Subiculum: styloid eminance round window niche post. lip bony ridge sinus tympani

Tympanic Isthmus Two openings between mesotympanum and attic Anterior isthmus Between tensor tympani tendon and the stapes

Posterior isthmus Between the short process of the incus and the stapedial tendon and pyramidal eminence

Prussaks space Prussaks space Laterally pars flaccida Medially the neck of the malleus Superiorly lateral malleal ligament Inferiorly the lateral process of the malleus

Facial nerve1. Intracranial(Pontine) segment - 23-24mm length - from brain stem to the internal auditory canal 2. IAC(Meatal) segment - 8-10mm length - from the fundus of the IAC to the meatal foramen - anterior superior part of IAC 3. Labyrinthine segment - 3-5mm length - from the meatal foramen to the geniculate ganglion - branch: GSPN

Facial nerve4. Tympanic segment - 8-12mm length - from first genu to second genu - inferior part of LSCC - Superior part of oval window 5. Mastoid segment - 10-15mm length - from second genu to stylomastoid foramen - chorda tympani 6. Extratemporal segment - from the stylomastoid foramen to the the muscles of innervation

Facial nerve

Dimensions of the Facial Nerve

Common Site of FN Injury during Otologic Surgery1) Intracranial segment: Brainstem-CPA lesions 2) Mastoid segment: Mastoidectomy 3) Tympanic segment - Stapedectomy - Labyrinthectomy (medial side) 4) Extracranial segment - Parotidectomy

Facial nerve geniculate ganglion Superior SCC

Common crus Lateral SCC Vestibular aqueduct Posterior SCC

Facial nerve tympanic segment Cochlea Lateral SCC Internal auditory canal