ANATOMY OF MID EAR and related structures

1. ANATOMY OF MIDDLE EAR
DR PINKY SHAH
DEPARTMENT OF E.N.T

2. ANATOMY OF MIDDLE EAR -MIDDLE EAR CLEFT
Middle ear cleft consists of:
• Tympanic cavity,
• Eustachian tube
• Mastoid air cell system.
The tympanic cavity is an irregular, air-filled
space within the temporal bone between
the tympanic membrane laterally and the
osseous labyrinth medially.
It contains the ossicles, muscles and
structures, like the tympanic segment of
the facial nerve
This Photo by Unknown Author is licensed under CC BY

3. • Measurements
vertical diameter :15 mm anteroposterior
diameter :15 mm transverse diameter
a)at roof :6 mm
b)in the centre :2 mm
c)at the floor :4 mm
• Communication
anteriorly :with nasopharynx
posteriorly :with mastoid antrum and mastoid air cells

4. ANATOMY OF MIDDLE EAR -TYMPANIC CAVITY
Tympanic cavity consist of three
compartments
1. Epitympanum (upper)
2. Mesotympanum (middle) and
3. Hypotympanum (lower)

5. ANATOMY OF MIDDLE EAR

7. ANATOMY OF MIDDLE EAR -THE LATERAL WALL
It is formed by the
• Bony lateral wall of the epitympanum superiorly(scutum)
• Tympanic membrane centrally and
• Bony lateral wall of the hypotympanum inferiorly.
Holes present in the bone of the medial surface of the lateral wall of
the tympanic cavity
• The petrotympanic fissure -anterior malleolar ligament and transmits the
anterior tympanic branch of the maxillary artery to the tympanic cavity.
• Anterior canaliculus (canal of Huguier) -chorda tympani nerve
• Posterior canaliculus.
Course of chorda tympani nerve

8. ANATOMY OF MIDDLE EAR -ROOF
The roof of the epitympanum is the tegmen tympani
• It is a thin bony plate that separates the middle ear space from the middle
cranial fossa.
• It is formed by both the petrous and squamous portions of the temporal bone
.
• The petrosquamous suture line.
• Veins from the tympanic cavity running to the superior petrosal sinus pass
through this suture line.

9. ANATOMY OF MIDDLE EAR -FLOOR
• The floor of the tympanic cavity separates the hypotympanum from the dome of
the jugular bulb.
• Occasionally, the floor is deficient and the jugular bulb is then covered only by
fibrous tissue and a mucous membrane.
• At the junction of the floor and the medial wall of the cavity there is a small
opening that allows the entry of the tympanic branch of the glossopharyngeal
nerve into the middle ear.

10. ANATOMY OF MIDDLE EAR -ANTERIOR WALL
• Narrow as the medial and lateral walls converge.
• The lower-third -thin plate of bone covering the carotid artery. It is perforated by
the – superior and inferior caroticotympanic nerves and tympanic branches of the
internal carotid artery.
• The middle-third - tympanic orifice of the Eustachian tube.
• Just above this is a canal containing the tensor tympani muscle
• The upper-third -pneumatized and may house the anterior epitympanic sinus, a
small niche anterior to the ossicular heads, which can hide residual
cholesteatoma in canal wall up surgery

11. ANATOMY OF MIDDLE EAR -MEDIAL WALL
.
• The medial wall separates the tympanic cavity from the
internal ear.
The promontory.
• It covers part of the basal coil of the cochlea . The
promontory gently inclines forwards to merge with the
anterior wall of the tympanic cavity

12. ANATOMY OF MIDDLE EAR-MEDIAL WALL
• Oval window behind and above the promontory, kidney-shaped opening that connects the
tympanic cavity with the vestibule, which is closed by the footplate of the stapes and its
surrounding annular ligament.
• The round window, subiculum , the ponticulus, the sinus tympani
• The facial nerve canal (or Fallopian canal) runs above the promontory and oval window in an
anteroposterior direction.
It is marked anteriorly by the processus cochleariformis
• The dome of the lateral semicircular canal.

13. ANATOMY OF MIDDLE EAR-MEDIAL WALL

14. ANATOMY OF MIDDLE EAR-MEDIAL WALL

15. ANATOMY OF MIDDLE EAR-POSTERIOR WALL
• The posterior wall is wider above than below
• Upper part a large irregular opening - the aditus ad antrum, that leads back from the
posterior epitympanum into the mastoid antrum
• Below the aditus is a small depression, the fossa incudis,.
• Below the fossa incudis and medial to the opening of the chorda tympani nerve is the pyramid,
• The canal within the pyramid curves downwards and backwards to join the descending portion
of the facial nerve canal.

16. ANATOMY OF MIDDLE EAR-POSTERIOR WALL
The Facial recess wall.
Boundaries –
• Medially by the facial nerve .
• Laterally by the tympanic
annulus,
• The chorda tympani nerve
running obliquely through
the wall between the two.

17. ANATOMY OF MIDDLE EAR-POSTERIOR WALL

18. ANATOMY OF MIDDLE EAR - POSTERIOR WALL
• The sinus tympani is a posterior extension of the
mesotympanum and lies deep to both the promontory and the
facial nerve.
• This extension of air cells into the posterior wall can be
extensive, and is probably the most inaccessible site in the
middle ear and mastoid.
• The sinus can extend as far as 9 mm into the mastoid bone
when measured from the tip of the pyramid.
• The medial wall of the sinus tympani becomes continuous with
the posterior portion of the medial wall of the tympanic cavity
where it is related to the oval and round window niches and the
subiculum of the promontory

19. ANATOMY OF MIDDLE EAR–
CONTENTS OF TYMPANIC CAVITY
Tympanic cavity contains
• The ossicles,
• Two muscles-tensor tympani and stapedius muscle
• Chorda tympani
• The tympanic plexus.
The ossicles are the malleus, incus and stapes that
form a semi-rigid bony chain for conducting sound
. The malleus is the most lateral and is attached to the
tympanic membrane, whereas the stapes is attached
to the oval window

20. ANATOMY OF MIDDLE EAR - EUSTACHIAN TUBE
• It is a dynamic channel that links the middle ear with the
nasopharynx from the middle ear at 45° and is turned forwards
and medially.
•
• Consists of two unequal cones, connected at their
apices. (36mm)
• The lateral third is bony and arises from the anterior wall of the
tympanic cavity(about 12mm)
• Medial two-thirds cartilagenous part.( 24mm)
• Its narrowest portion is called the isthmus, where the diameter
is only 0.5 mm or less.

21. ANATOMY OF MIDDLE EAR- EUSTACHIAN TUBE
• In the nasopharynx, the tube opens 1-1.25 cm behind and below the posterior end of the
interior turbinate.
• The opening is triangular in shape and is surrounded above and behind by the torus.
• The salpingopharyngeal fold stretches from the lower part of the torus downwards to the wall
of the pharynx.
• The levator palati, as it enters the soft palate, results in a small swelling immediately below
the opening of the tube.
• Behind the torus is the pharyngeal recess or fossa of Rosenmuller.
• Lymphoid tissue is present around the tubal orifice and in the fossa of Rosenmuller,
and may be prominent in childhood.

22. ANATOMY OF MIDDLE EAR- EUSTACHIAN TUBE
• It is lined with respiratory mucosa containing goblet cells and mucous glands, having
ciliated epithelium on its floor.
• At its nasopharyngeal end, the mucosa is truly respiratory; but in passing along the tube
towards the middle ear, the number of goblet cells and glands decreases, and the ciliary
carpet becomes less profuse.
• It runs through the squamous and petrous portions of the temporal bone, gradually
tapering to the isthmus.
• A thin plate of bone forms the roof, separating the tube from the tensor tympani muscle
above.
• The carotid canal lies medially and can impinge on the bony Eustachian tube.

23. ANATOMY OF MIDDLE EAR -BLOOD SUPPLY
• Arise from both the internal and external carotid system.
• The overlap is extensive and great variability is present.
• Supply is from the anterior tympanic, stylomastoid, maxillary, posterior auricular, middle
meningeal, ascending pharyngeal, artery of pterygoid canal and internal carotid arteries.
• The anterior tympanic and stylomastoid arteries are the biggest.
• Anterior tympanic artery br. of Maxillary Artery supplies ant part of Tympanic membrane;
malleus and incus; anterior part of tympanic cavity.
• Stylomastoid artery br. of Posterior Auricular artery supplies Posterior part of tympanic
cavity; stapedius muscle and
Mastoid air cell

24. MASTOID
CONSIST OF 3 PARTS
1 ) ADITUS AD ANTRUM
2)MASTOID ANTRUM
3)MASTOID AIR CELLS

25. MASTOID-ADITUS AD ANTRUM
▪ It is a short canal connecting epitympanum
with mastoid antrum.
▪ Short process of incus lies on its floor.
▪ Facial nerve runs in its canal in the floor
▪ Lateral semicircular canal lies in its medial
wall.

26. MASTOID ANTRUM
• The mastoid antrum is an air-filled sinus in the petrous part of temporal bone.
• It communicates with the middle ear by the aditus.
• Antrum is well developed at birth.
•
• Volume = 2 ml (adult).
• The roof of the mastoid antrum and mastoid air cell space form the floor of the
middle cranial fossa.
• The medial wall relates to the posterior semicircular canal.
• More deeply and inferiorly is the dura of the posterior cranial fossa and the
endolymphatic sac

27. MASTOID ANTRUM
• Posterior to the endolymphatic system is the sigmoid sinus, which curves
down, pass medial to the facial nerve and then becomes the dome of the
jugular bulb in the middle ear space
• The posterior belly of the digastric muscle forms a groove in the base of the
mastoid bone
• The digastric ridge inside the mastoid lies lateral to the sigmoid sinus and
the facial nerve and is a useful landmark for finding the nerve
• The periosteum of the digastric groove continues anteriorly and part of it
becomes the endosteum of the
stylomastoid foramen and subsequently of the facial nerve canal.

28. MASTOID ANTRUM
Macewen's triangle is a direct lateral relation to the
mastoid antrum.
In most individuals, the mastoid air cell system
is fairly extensive with air cells
Normally, lining of the mastoid is a flattened,
nonciliated
epithelium without goblet cells or mucus glands.

29. MASTOID AIR CELL.

30. MASTOID AIR CELL.
The extent of pneumatization of the temporal bone varies according to heredity, environment, nutrition, infection,
and eustachian tube function.
There are five recognized regions of pneumatization:
• Middle ear,
• Mastoid,
• Perilabyrinthine,
• Petrous apex, and
• Accessory.
There are five recognized air cell tracts.
• The posterosuperior tract
• The posteromedial cell tract
• The subarcuate tract.
• The perilabyrinthine tracts
• Peritubal tract surrounds the eustachian tube.

31. MIDDLE EAR- APPLIED ANATOMY
-Middle ear transformer mechanism
▪ Divided into 3 stages:
▪ provided by ear drum (catenary lever)..ratio
▪ Provided by ossicles(ossicular lever) provides mechanical
advantage is 2.3
▪ Provided by difference in surface area between tympanic
membrane and footplate of stapes(hydraulic lever) depends on
areal ratio.transformer ratio is 18:1
▪ Phase difference
▪ Stapedial reflex

32. Functions of Eustachian tube-
▪ Ventilation of middle ear cleft-plays an important role in equalising
middle ear pressure with atmospheric pressure.
▪ Prevents reflux of nasopharygeal secretions
▪ Clearance of middle ear secretions

33. ▪ Impedance audiometry
Important landmarks in middle ear surgeries
▪ Prussacks space- cholestatoma
▪ Sinus tympani-residual cholesteatoma
▪ Oval window , processus cochleariformis and 1st genu-landmark for facial nerve.
▪ Facial recess-residual cholesteatoma and posterior tympanotomy approach.
▪ Trautmann’s triangle- infection reaches cerebellum through posterior cranial fossa.
▪ Korners septum,Spine of Henle, Macewan’s triangle –landmarks to locate mastoid
antrum.
▪ Donaldson line-inferior to this line is the endolymphatic sac .

34. Thank You