The middle ear cleft consists of the tympanic cavity, mastoid air cell system, and Eustachian tube. The tympanic cavity contains the auditory ossicles (malleus, incus, stapes) and is bounded laterally by the tympanic membrane. It communicates anteriorly with the Eustachian tube and posteriorly with the mastoid air cells. The cavity contains the tensor tympani and stapedius muscles and is divided into 3 parts - epitympanum, mesotympanum, and hypotympanum. The ossicles transmit sound from the tympanic membrane to the oval window of the inner ear.

2. MIDDLE EAR CLEFT
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Eustachian Tube
Tympanic Cavity
Mastoid Air Cell System , Aditus ,
Antrum

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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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

8.  Hypotympanum:
 situated below the level of tympanic membrane.
 Lined by ciliated columnar 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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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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18. Tympanic segment of facial nerve
 Facial Nerve canal (Fallopian Canal)
 Above promontory & Oval Window it runs anteroposteriorly
 Marked anteriorly by processus cochleariformis: (constant
landmark)
 Geniculate ganglion- above processus cochleariformis
 Behind Oval Window it runs inferiorly
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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

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.

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.

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