1. Cummings Ch 127: T-Bone and Ear Anatomy
Sameer Ahmed
9/25/2013

2. The temporal bone consists of four embryologically distinct components:
Squamous, mastoid, petrous, and tympanic parts
A horizontal ridge known as the temporal line is formed along the most inferior insertion by the temporalis muscle
Aligned with the zygomatic process,
Surface landmark that estimates the location of the middle fossa floor (Tegmen)
“The middle fossa dural plate (MFD) is located on average 5 mm above the LTI (linea tempralis inferior)”
“This study confirms that the mastoid antrum is located 15 mm deep to the lateral surface of the mastoid bone”

3. Facial Nerve Course Cisternal segment/intracranial segment
Brainstem to IAC --> mm
Meatal segment → 8mm
Porus acoustics: Medial IAC
Fundus: Lateral IAC
Labyrinthine segment → 5mm
Fundus to geniculate ganglion(1st genu)
Tympanic segment → 8-11mm
Geniculate to 2nd genu
Courses above oval window; dehisc 50% of time
2nd genu is just anteroinferior to the horizontal SCC
Vertical segment → 10-14mm
2nd genu to stylomastoid foramen

5. At the fundus (lateral IAC)
Bill's Bar separates CN 7 anteriorly from SVN
“Jail Bar”
Falciform cr. separates CN 7 from cochlear n.; SVN from IVN
Anatomic relationship changes closer to the brainstem

6. Inferior limit for a translab approach to IAC Cochlear aqueduct
Jugular foramen:
Pars nervosa: CN X, CN XI, Arnold's nerve, jugular bulb, and posterior meningeal branch of ascending pharyngeal artery
Pars venosa: CN IX, Jacobson nerve, and venous return from inferior petrosal sinus
Inferior limit for a translab approach to IAC
Cochlear aqueduct
The cochlear aqueduct eventually opens into the scala tympani at the cochlear base
Keel: Ridge of bone between Jugular bulb and ICA

7. EAC: Lateral cartilaginous: 1/3rd Medial bony: 2/3rd
Lateral canal skin thicker, more sebaceous units
Medial bony: 2/3rd
Think skin; continuous with TM epithelium
Bony-cartilaginous junction in EAC
Site of granulation tissue in malignant OE
Routes of tumor/infxn spread
Foramen of Hushke
Incomplete ossification of bony anterior EAC; medial
Fissures of Santorini
Defects in cartilaginous EAC

8. 1st and 2nd branchial arches → external ear
6 Hillocks of His
1st branchial arch: 1-3 hillocks (tragus, superior helix)
2nd branchial arch: 4-6 hillocks (antihelix, antitragus, lobule, and inferior helix)
External ear blood supply
Posterior auricular & Superficial temporal art.

9. Tympanic Membrane Outer layer: epidermal/squamous (ectoderm)
Middle layer: fibrous (mesoderm)
Can be subdivided into radial outer and circular inner
Inner layer: mucosal (endoderm)
Fibrous annulus: thickened pars tensa forming a fibrous outler ring for the attachement to the T- Bone; lies within tympanic sulcus except superiorly where it is deficient at the Notch of Rivinus
Pars flaccida = Shrapnell's Membrane

10. Eustachain Tube Medial 1/3rd → Bony Lateral 2/3rd → Cartilaginous
Collapsed at rest
Tensor veli palatini intermittenly enlarges ET during yawning or swallowing
Bony cartilaginous jnxn of ET is the narrowest portion of the ET
Carotid artery is just medial to ET

11. Middle Ear Relative to tympanic annulus Mestoympanum
Epitympanum: above annulus
Mesotympanum: confined by the annulus
Hypotympanum: below annulus
Mestoympanum
Anterior limit: ET
Posterior limit: Facial nerve
Medial wall: Cochlear promontory
Postero-superior: Oval window
Postero-inferior: Round window
Sinus tympani: posterior to both windows and medial to vertical division of FN
Pyramidal eminence: anterior to 2nd genu

12. Hypotympanum Epitymapnum Limited inferiorly by the jugular bulb
Superior-medial wall of bony EAC (scutum) forms the lateral wall of the epitympanum
Epitympanum divided into 3 spaces:
Prussak's space, just medial to pars flaccida and lateral to the head and neck of the malleus;
The compartment anterior to the malleus
The posterior compartment, which communicates with the antrum
Attic Cholesteatomas can spread postero-superiorly into the antrum or postero-inferiorly into posterior mesotympanum

13. Ossicles Malleus Manubrium (handle; tip is the umbo)
Lateral/short process
Anterior process
Head
Neck
Tensor tympani attaches to malleus neck and manubrium by a tendon originating from the cochleariform process

14. Incus Body Short process Long process Lenticular process
Diarthrodial joints (for malleus-incus and incus-stapes connections)

15. Stapes Head (capitulum) Anterior and posterior crus Footplate (base)
Stapes footplate attaches to bony margin of oval window via an annular ligament (syndesmosis joint)