anatomy and relations of middle ear

1. ANATOMY OF
MIDDLE EAR
By – Dr. B. Nitin

2. CONTENTS OF MIDDLE EAR -
 OSSICLES
 MIDDLE EAR MUSCLES
 EUSTACHIAN TUBE
 MIDDLE EAR CAVITIES
 MASTOID

3. RELATIONS :-
 Largely by tympanic membrane
 Lesser extend by bony outer attic wall (SCUTUM)
 Chorda tympani nerve passes across-lateral to
long process of incus & medial to handle of
malleus.
LATERAL WALL -

4. MEDIAL WALL -
• Promontory
• Oval window (fenestra vestibuli)
• Sinus tympani
• Round window (fenestra cochleae)
• Facial nerve canal (above oval window)
• Processus cochleariformis (hook like projection,
housing tensor tympani muscle)
•Prominence of lateral semicircular canal.

5.  Formed by Tegmen tympani (both petrous and
squamous portion of temporal bone form it)
 Separates tympanic cavity from middle cranial fossa. Also forms roof of aditus and
antrum.
ROOF -

6.  Formed by thin plate of bone separates
the hypotympanum from the dome of jugular bulb.
 Maybe congenitally deficient – jugular bulb is separated by mucosa.
 Tympanic branch of glossopharyngeal nerve pierces floor between jugular fossa and
lower opening of carotid canal.
FLOOR -

7.  Thin plate of bone separating from internal carotid artery.
 2 openings:
Lower-Eustachian tube
Upper-Canal of Tensor tympani muscle
ANTERIOR WALL -
ANTERIORWALL

8.  Pyramid-bony projection; stapedius tendon
appears through its summit, gets attached to neck of stapes.
 Aditus-opening through which attic communicates with the antrum.
 Fossa incudus-close to aditus, lodges short process of incus.
 Vertical part of facial canal behind pyramid.
 Posterior canaliculus- aperture for emergence of chorda tympani.
POSTERIOR WALL -

10. EAR OSSICLES – MALLEUS
 8 to 9 mm long and weighs 25 mg.
 Head -> articulate incus
 Manubrium -> embedded between fibrous and mucous
membrane layers of the eardrum.
 Neck
 Lateral process
 Anterior process near the junction of the neck and manubrium

11. INCUS
 7 mm long and weighs 30 mg.
 Short process -> is posteriorly oriented and is accommodated by the
fossa incudis on the back wall of the middle ear.
 Body
 Long process -> descends to end at a rounded nodule called the
lenticular process -> articulates with the head of the stapes

12. STAPES -
 3.5 mm long, and the footplate surface area of 3.2 mm²
weighs 3 to 4 mg.
 Head is connected via the neck to two crura -> anterior and
posterior crura, which lead down to footplate.
 Obturator foramen ->Central
 attached to the oval window by the annular ligament

13. Ligaments attached to Ossicular chain and middle ear walls:
 Superior malleal ligament -> from the roof of the attic down to the
head of the malleus.
 Anterior malleal ligament from the anterior tympanic wall to the
anterior process of the malleus.
 Lateral malleal ligament -> from the bony margin of the notch of
Rivinus to the neck of the malleus.
 Posterior incudal ligament (actually a fold of mucous membrane
rather than a ligament) runs from the fossa incudis to the short
process of the incus

14. MIDDLE EAR MUSCLES
Tensor tympani muscle:
 It is housed within the tensor tympani semicanal superior to the Eustachian tube. 25cm
long
 Origin: from the
I. cartilage of the ET,
II. walls of its semicanal
III. sphenoid bone adjacent to it
a) Tendon bends around cochleariform process and proceeds to insert on the malleus at
the top of the manubrium near the neck.
b) Contraction of the tensor tympani -> stiffening the ossicular chain.
c) Innervated by the Mandibular nerve by the way of a branch from the med pterygoid
nerve

15. Stapedius muscle
 The smallest skeletal muscle in the body
 length -> 6.3 mm.
 Innervation: the facial nerve.
 The stapedius tendon from pyramidal eminence apex -> runs anteriorly to
insert on the neck of the stapes posteriorly.
 Contraction of the stapedius (> 80 dB) pulls the stapes posteriorly ->
stiffening the ossicular chain -> reduce the energy that is delivered to the
inner ear.
 Gain control mechanism -> keep cochlear input constant -> ↑ dynamic range
 ↓ self generated noise (chewing, vocalization)

16. EUSTACHIAN TUBE -
Function -
I. Aeration and drainage of the middle ear.
II. equalize air pressure to be the same on both sides of the eardrum.
ARISES FROM -
i. From the anterior middle ear wall to the posterior wall of the nasopharynx
ii. Tilting downward at an angle of 45°.
 Eustachian tube is almost horizontal in infants and young children.
a) The first third of the tube -> surrounded by bone (3- 6mm in diameter),
b) The remainder is surrounded by an incomplete ring of elastic cartilage. The meeting
point -> called the isthmus (1-2 mm diameter).
c) The cartilaginous part forms a valve that protect middle ear from pressure fluctuations
in the pharynx and decreases transmission of a person’s voice to the middle-ear cavity.
d) It has cilia that propel mucus from the middle ear to the nasopharynx.
e) The slit shaped cartilaginous part of the Eustachian tube allows transport of material
from the middle-ear cavity to the nasopharynx but not the other way.

17. f) At rest, the cartilage keeps the Eustachian tube closed.
g) The lumen of the tube is opened by the pull exerted by the tensor palatini
muscle. This occurs during swallowing, yawning…
h) Negative pressure develops in the middle ear ->when this mechanism fails to
open the Eustachian tube frequently and effectively
i) The tube is lined with respiratory mucosa containing goblet cells & mucous
glands.

19. MIDDLE EAR CAVITIES
1. Mesotympanum -> between the tympanic membrane and the wall of the
inner ear -> at level of parstensa. -> divided into 3 pouches (Inferior Incudal
Space, Ant. and Post. Pouches of Von Troeltsch).
2. Epitympanum -> contain the head of the malleus and body of incus -> above
level of pars tensa. ->include (Prussak’s space and attic compartment (ant.
and post. By sup malleolar fold).
3.Hypotympanum -> ET (area around it called protympanum) and lower part of
middle ear cavity below tympanic membrane level.
• The total volume of the middle-ear cavities -> 2 cm³
• If the volume of the mastoid air cells is included -> Total volume 10 cm³

20. MASTOID
 Middle ear, antrum, and air cells compose a
continuous, air-filled system->infection can spread
from ME to the mastoid air cell system and beyond.
 Mastoid -> interconnecting air cells that vary widely
in size, shape, and number. and according to
cellularity –
*Well Pneumatized
*Diploetic
*Sclerotic

21. Classified According to their location into:
a) Zygomatic cells (in root of zygoma)
b) Tegmen cells
c) Perisinus cells
d) Perilabyrinthine cells
e) Peritubal cells
f) Tip cells
g) Marginal cells
h) Squamous cells.

22.  Aditus ad antrum connects the antrum with the attic or upper part of the middle ear
cavity.
 Antrum:
• The roof -> a thin bony plate -> tegmen tympani, which separates them from ->
middle cranial fossa.
• Its medial wall separates it from: - lateral SCC. - Endolymphatic Sac - Dura of
posterior cranial Fossa
• Lat. Wall: 1.5 cm thick of squamous bone and Mac Ewen’s Triangle bounded by
(linea Temporalis, posterosuperior margin of Ext. aud. Canal, Tangent of posterior
margin of ext. aud. Canal)
• Anteriorly: from medial to lateral ( Facial n. canal,,, Aditus ad antrum and facial
recess, deep bony EAC).
• Posteriorly: mastoid bone and air cells and Sigmoid Sinus
• Floor: Jugular bulb medial to facial canal - Digastric ridge - origin of sternomastoid
m.

25.  Mastoid develop from Squamous and petrous bone -> sometimes
petrosquamous suture persists as bony plate called “Korner’s
Septum” separates superficial squamous cells from deep petrosal
cells making surgery difficult

26.  Blood supply of ET: Ascending pharyngeal artery ,Middle meningeal artery
and Artery of pterygoid canal

27. LYMPHATIC DRAINAGE -
Middle ear :
 Retropharyngeal & parotid nodes
ET :
 Retropharyngeal group of nodes

28. MUCOSA OF MIDDLE EAR -
 Mucus membrane of the nasopharynx is
continuous with that of middle ear ,aditus and
antrum.
 Middle ear cavity is lined by –
1) Ant and Inf part – Ciliated columnar
2) Post part – Cuboidal
3) Attic and Mastoid air cells – flat, non ciliated
4) ET – Ciliated pseudo stratified columnar
epithelium.

29. It enters the tympanic cavity from
the posterior canaliculus at the
junction of the lateral and
posterior walls.
 It runs across the medial surface
of the tympanic membrane
between the mucosal and fibrous
layers.
 Then passes medial to the upper
portion of the handle of the
malleus above the tendon of
tensor tympani.
 leaves thorough petrotympanic
fissure.
 carries taste sensation from the
anterior two-thirds of the same
side of the tongue and
secretomotor fibres to the
submandibular gland.
THE CHORDA TYMPANI NERVE

30. THE TYMPANIC PLEXUS
 It is formed by the
– tympanic branch of the glossopharyngeal nerve
(Jacobson's nerve)
– caroticotympanic nerves, which arise from the
sympathetic plexus around the internal carotid artery.
 The nerves form a plexus on the promontory and provide the
branches to the mucous membrane lining the tympanic cavity,
Eustachian tube and mastoid antrum and air cells.
 The plexus also provides branches to join the greater superficial
petrosal nerve and the lesser superficial petrosal nerve that
contains all the parasympathetic fibres of the glossopharyngeal
nerve.

31. FACIAL RECESS -
 Depression on posterior wall,
lateral to pyramid.
 Shallow lower down
 Medially - facial nerve
 Laterally – chorda tympani
 Above – fossa incudis
 Posterior tympanotomy-direct access
to middle ear without disturbing
posterior wall.

32. SINUS TYMPANI -
 Boundaries:
– Superior: Ponticulus
– Inferior: Subiculum
– Lateral: Mastoid Segment of Facial
Nerve
– Medial: Posterior semicircular canal
 It evades direct surgical visualization during
surgery. Site for cholesteatoma recurrence

33. PROMONTORY -
 Formed by basal turn ofcochlea
 Contains nerves forming tympanic plexus
 Tympanic branch of ninth nerve may be covered by
bone forming a small canal.

34. OVAL WINDOW -
 Behind and above the
promontory.
 Connects tympanic cavity with
the vestibule.
 Closed by footplate of stapes
and annular ligament.

35. ROUND WINDOW -
 Lies below and behind the promontory.
 Separates middle ear from Scala tympani.
 Closed by fibrous secondary tympanic
membrane.lying between round & oval
window.

36. EMBRYOLOGY -

37. First pharyngeal pouch -Pharyngotympanic tube
Middle ear cavity
Mastoid antrum
(dorsal expansion of cavity)
First pharyngeal arch -Malleus
Incus
Tensor tympani muscle
Malleolar ligaments
Second pharyngeal arch - Stapes
Stapedius muscle
Stapes develop from the second arch except its footplate and annular ligament which
are derived from the ottic capsule.
First pharyngeal membrane -Tympanic membrane

38. Maxillary