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 를 기준으로 sup 와

inf, • facial canal 을 중심으로 lat 과 med 로 구분 • Superolateral : facial sinus • Inferolateral : lateral tympanic sinus • Superomedial : posterior tympanic sinus • Inferomedial : sinus tympani

• Ponticulus : pyramidal eminance 에서 promontory 로 이어지는 bony ridge

• Subiculum : styloid eminance 에서 round window niche 의 post. lip 으로 이어지는 bony ridge – 이사이에 가장 큰 sinus tympani 존재

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

Prussak’s space

• Prussak’s space– Laterally pars flaccida– Medially the neck of the malleus– Superiorly lateral malleal ligament– Inferiorly the lateral process of the malleus

Facial nerve

1. Intracranial(Pontine) segment - 23-24mm length - from brain stem to the internal auditory canal2. IAC(Meatal) segment - 8-10mm length - from the fundus of the IAC to the meatal foramen - anterior superior part of IAC3. 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

1) Intracranial segment: Brainstem-CPA lesions2) Mastoid segment: Mastoidectomy3) Tympanic segment - Stapedectomy - Labyrinthectomy (medial side)4) Extracranial segment - Parotidectomy

Common Site of FN Injury during Otologic Surgery

Posterior SCC

Superior SCC

Common crus

Lateral SCCVestibular aqueduct

Facial nerve geniculate ganglion

Facial nerve tympanic segment

Lateral SCC

Internal auditory canal

Cochlea