3. TYMPANIC CAVITY
Irregular air filled space ,within temporal bone.
Bounded laterally by Tympanic Membrane.
Medially by osseous labyrinth.
Contains auditory ossicles, middle ear muscles.
Tympanic segment of VII CN run along the medial wall
Communications:
- Anteriorly - Eustachian tube
- Posteriorly - Antrum, mastoid air cells through aditus.
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4.
5.
6. 3 parts:
Epitympanum:
Situated above the malleolar folds of tympanic membrane.
It contains the head of malleus, incudomalleolar joint and body
and short process of incus.
Lined by the pavement epithelium.
7. Mesotympanum:
situated medial to the pars tensa of tympanic membrane.
Middle ear proper is lined by cuboidal epithelium
9. LATERAL WALL
Formed by
1. Bony lateral wall of Epitympanum superiorly.
2. Tympanic membrane centrally.
3. Bony lateral wall of hypotympanum inferiorly.
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10. TYMPANIC MEMBRANE
Thin oval in shape
9-10mm x 8-9mm
550 with floor
Circumference thickened to form fibrous annulus which anchors it
to tympanic sulcus
Superiorly becomes a fibrous band Anterior Malleal Fold (AMF) &
Posterior Malleal Fold (PMF)
-triangular TM above the fold called as Pars Flaccida
(Sharpnell’s membrane)
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11. ROOF
Formed by Tegmen tympani
Separates tympanic cavity from MCF dura
Formed by Petrous & Squamous part of temporal
bone
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12. FLOOR
Thin plate of bone separating the tympanic cavity
from the dome of the Jugular bulb
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13. ANTERIOR WALL
Separates middle ear cavity from ICA.
Lower one third perforated by
Superior and Inferior Carotico
tympanic Nerves to Tympanic plexus.
Tympanic branches of ICA
Middle One third
Canal of Tensor Tympani muscle above
Tympanic orifice of Eustachian Tube below
Upper One Third
Pneumatized
May house anterior epitympanic sinus – can hide residual
cholesteatoma.
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14. MEDIAL WALL (Surgical floor of middle ear)
Separates tympanic cavity from inner ear
Promontory: rounded elevation
Formed by part of basal turn of cochlea.
Surface contains tympanic plexus
Tympanic branch of glossopharyngeal nerve
Carotico-tympanic nerve
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15.
16. Fenestra vestibuli (Oval Window)
Behind & above promontory
Oval shaped: 3.25 x 1.75 mm,
Above it lies tympanic part of facial nerve
Closed by foot plate of stapes & surrounded by
annular ligament
17. Fenestra cochlea (Round Window)
Below & behind Oval window
The round window is posteroinferior to the promontory
Separated by posterior extension of promontory - Subiculum
Ponticulus : spicule of bone from promontory to pyramid
RW membrane (2.3*1.9mm) is covered by bony overhang
from promontory.
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19. The posterior wall can be divided into two distinct parts:
The upper third which corresponds to the aditus ad
antrum and represents the posterior limit of the
epitympanum
The lower two thirds which correspond to the posterior
wall of the retrotympanum.
POSTERIOR WALL
20. Aditus: aditus ad antrum connects middle ear space
with mastoid antrum. Dimension 4 × 4 × 4 mm
Fossa incudis: lodges short process of incus and
posterior ligament.
Pyramid: contains stapedius muscle.
Recess:
Facial recess
Sinus tympani
21. Posterior wall eminences
The pyramidal eminence
The pyramidal eminence is situated at the centre of the
posterior wall immediately behind the oval window; it is
about 2 mm height.
It lodges the body of the stapedial muscle and its apex
gives passage to the stapedial tendon. The pyramidal
eminence communicates with the facial bony canal by a
minute aperture which transmits the stapedial branch of
the facial nerve
22. The styloid eminence
The styloid eminence or Politzer eminence is a
recognized smoothed elevation at the inferior part of the
posterior wall; it represents the base of the styloid
process.
23. Facial recess (suprapyramidal recess): lies lateral to facial
nerve.
Boundaries: Fossa incudis superiorly
Chorda tympani laterally
Facial nerve medially
Sinus tympani (infrapyramidal recess): the niche of two
labyrinthine windows communicate posteriorly with this
deep recess
Boundaries :
-Laterally bounded by vertical segment of the facial nerve.
-Medially by the oval window.
-Superiorly by ponticulus and inferiorly by subiculum.
-Can be up to 9 mm deep from the tip of pyramid.
24. CONTENTS
Three bones:
Malleus
Incus
Stapes
Two muscles:
Tensor tympani
Stapedius
Two nerves:
Tympanic plexus
Chorda tympani
25. MALLEUS (HAMMER)
Largest and lateral most
9mm length
Head , neck , handle/manubrium , anterior and lateral process.
Head
- Lies in epitympanum
- Has a saddle shaped facet articulating with body of incus – synovial
joint.
Handle
- Runs between mucosal and fibrous layers of TM.
- Upper part of medial surface gives insertion to tensor tympani muscle
26.
27. INCUS (ANVIL)
Body, short process, long process
Body – In epitympanum , suspended by superior incudal
ligament attached to tegmen tympani.
Short Process projects into attic ,lies in fossa incudis
Long Process descends into mesotympanum.
- have lenticular process at its tip – articulates with stapes.
- Lenticular process sometimes called fourth ossicle because
of its incomplete fusion with tip.
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29. STAPES (STIRRUP)
Shaped like stirrup, smallest
Head, neck, anterior and posterior crura, foot plate.
Head – articulates with lenticular process
Stapedial tendon attaches to neck and upper portion of
posterior crura.
Foot Plate – 3mm long , 1.4 mm wide
- lies in oval window, attached to bony margin
by annular ligament.
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31.
32. MUSCLES OF MIDDLE EAR
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Stapedius
Arises from the walls of conical cavity within
pyramid.
Inserts into neck of stapes.
Nerve supply: small branch of facial nerve.
Tensor tympani
Arises from walls of the bony wall
lying above the Eustachian tube.
Inserts into upper end of malleus handle.
Nerve supply: Branch of mandibular nerve.
33. MASTOID ANTRUM
Communicates with middle ear via the aditus.
Antrum is well defined at birth.
Measurements:
Volume: 1ml
Antero-posterior diameter: 14mm
Vertical diameter: 9mm
Transverse diameter: 7mm
34. Relations
Medial wall : Lateral semicircular canal and more
deeply to posterior cranial fossa and endolymphatic
sac
Roof : Middle cranial fossa
Posterior wall : sigmoid sinus
Lateral wall : Thickness at birth 2mm, adult life 12-
15mm, corresponds to suprameatal/Macewen’s
triangle.
Floor: Digastric muscle laterally and sigmoid sinus
medially.
35. SUPRAMEATAL / MACEWEN’S TRIANGLE
Region felt through the cymba conchae of the auricle.
Bound by the suprameatal crest, posterosuperior margin of
the external meatus and a vertical tangent through the
posterior margin of the external meatus.
In adults, antrum lies 1.5-2cm deep to Macewen’s triangle
Landmark in cortical mastoidectomy.
36. It is a shallow closed space that lies in between the pars
flaccida and the neck of the malleus
Roof - lateral mallear fold
Floor – lateral process of malleus along with its mucosal folds
lying in horizontal plane
Through the gap present between lateral malleal and lateral
incudal folds, Prussaks space communicates with the attic
The most common site for origin of cholesteatoma