Middle ear anatomy

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• Auditory tube
• Tympanic Cavity
• Aditus
• Mastoid Air Cells

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The eustachian tube ,tympanic cavity ,attic,mastoid air cells
develop from the endoderm of tubotympanic recess which
arises from the first pharyngeal pouches.

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Malleus and incus are derived from mesoderm of the first
arch while the stapes develop from the second arch except its
footplate and annular ligament which are derived from the ottic
capsule.

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• 36 mm long in adults
• Directed anteriorly, inferiorly & medially from
anterior wall of M.E., forming angle of 450 with
horizontal & sagittal planes
• Enters naso-pharynx 1.25 cm behind posterior
end of inferior turbinate

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Lateral 1/3 is bony
Medial 2/3 is fibro-
cartilaginous.
Junction b/w 2 parts
is isthmus,
narrowest part of
Eustachian Tube.

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Anatomy of
cartilaginous part:
Cartilage plate lies
postero-medially &
consists of medial +
lateral laminae
separated by elastin
hinge. Fibrous tissue +
Ostmann’s fat pad lie
antero-laterally.

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CHARACTERISTIC ADULT INFANT
Length 36 mm 18mm
Angle with horizontal 45° 10°
Lumen Narrow Wide
Angulation at Isthmus Present Absent
Cartilage Rigid Flaccid
Elastic recoil Effective Ineffective
Ostmann’s fat More Less
Difference in adult & infant<7years ET

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Blood supply of ET:
• Ascending pharyngeal artery
• Middle meningeal artery
• Artery of pterygoid canal
• Veins drain into pterygoid venous plexus

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• Pearly white semi-
translucent membrane
• Obliquely placed
faces
laterally,inferiorly
,anteriorly
• 2 parts : pars tensa &
pars flaccida
• 3 layers of pars tensa
: outer epithelial,
middle fibrous & inner
mucosal

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• Fibrous layer is
disorganized in pars
flaccida (Sharpnell’s
membrane)
• Pars tensa thickened
peripherally into
fibrocartilagenous annulus
called annulus tympanicus
which fits into tympanic
sulcus of temporal bone.
• Annulus deficient
superiorly in pars flaccida
and is called notch of
Rivinus

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Nerve supply of TM:
• Anterior half of lateral surface :
Auriculo temporal nerve
• Posterior half of lateral surface :
Auricular branch of vagus
• Medial surface :
Tympanic branch of
glossopharyngeal nerve(jacobson
nerve)
V
X

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• Epitympanum
• Mesotympanum
• Hypotympanum
Parts of tympanic cavity:

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Walls of the tympanic cavity:
Lateral
Medial
Posterior
Anterior
Roof
Floor

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ROOF
• Thin plate of bone called TEGMEN
TYMPANI .
• It also extends posteriorly to form the roof
of the aditus and antrum.
• It seperates tympanic cavity from the
middle cranial fossa.

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The floor
• Thin plate of bone which seperates
tympanic cavity from the jugular bulb.
• Near the medial border of the floor is a
small aperture, through which the
tympanic branch from the
glossopharyngeal nerve [IX] enters the
middle ear

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The anterior wall
Lower part
• Thin plate of bone which separates the
cavity from the internal carotid artery.

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The anterior wall
Upper part
• Canal of tensor tympani muscle.
• Eustachian tube opening

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Lateral wall
Bony :
• Lateral attic wall above pars flaccida
• lateral wall of hypotympanum
Membranous :
• Tympanic membrane

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Medial wall
• Promontory
• Oval window
• Round window
• Tympanic part of bony facial nerve canal
• Lateral semicircular canal
• Processus cochlearformis

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 The promontory
is a rounded
elevation
occupying much
of the central
portion of the
medial wall.
 formed by basal
turn of cochlea
 usually has small
grooves on its
surface
containing the
nerves which
form the
tympanic plexus

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Oval window
 lies Behind and above the promontory
 A kidney-shaped opening that connects
the tympanic cavity with the vestibule.
 Close by a footplate of the stapes.
 Its size average 3.25 mm long and 1.75
mm wide.

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Round window
• Lies below and behind the
oval window
• Separated by subiculum(post
extension of promontory)
• Ponticulus.another ridge
above subiculum and runs to
pyramid on the posterior wall
• Sinus tympani is where
ponticulus and subiculum
meet
• RWM is 2.3×1.9.
• It is placed at right angles to
plane of stapes foot plate

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Facial nerve canal
• The facial nerve canal (or Fallopian canal) runs
above the promontory and oval window in an
anteroposterior direction.
• The facial nerve canal is marked anteriorly by the
processus cochleariformis, a curved projection
of bone, concave anteriorly, which houses the
tendon of the tensor tympani muscle as it turns
laterally to the handle of the malleus.
• The region above the level of the facial nerve canal
forms the medial wall of the epitympanum.
• Behind the oval window, the facial canal starts to
turn inferiorly as it begins its descent in the
posterior wall of the tympanic cavity.

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• The dome of the lateral semicircular canal
is the major feature of the posterior portion
of the epitympanum, lying posterior and
extending a little lateral to the facial canal

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Posterior wall
• Aditus ad antrum
• Fossa incudis for short process of incus
• Bulge produced by lateral semicircular canal
• Pyramidal eminence for stapedius tendon
• Buldge produced by vertical part of facial
nerve
• Sinus tympani
• Facial recess

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 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,
which houses the short process of the incus and its
suspensory ligament.
 Below the fossa incudis and medial to the opening of the
chorda tympani nerve is the pyramid, a small hollow conical
projection with its apex pointing anteriorly.
 This houses the stapedius muscle and tendon, which inserts
into the posterior aspect of the head of stapes.
 The canal within the pyramid curves downwards and
backwards to join the descending portion of the facial nerve
canal.

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Facial Recess
 The facial recess is bounded:
– Medially by the facial
nerve and
– Laterally by the tympanic
annulus,
– with the chorda tympani
nerve running obliquely
through the wall between
the two.
 The chorda always runs
medial to the tympanic
membrane.
The facial recess is a groove which lies between the pyramid with facial
nerve, and the annulus of the tympanic membrane .

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Facial Recess
The angle between the facial nerve and the chorda allows a posterior
tympanotomy, allowing access to the middle ear from the mastoid
without disruption the tympanic membrane.

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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

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Contents of middle ear cavity
• Air
• 3 ossicles : malleus, incus and stapes
• 2 muscles : tensor tympani & stapedius
• 2 nerves : chorda tympani & tympanic
plexus
• Mucosal folds & ligaments
• Blood vessels

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•
ossicles

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MUSCLE ORIGIN INSERTION NERVE
SUPPLY
ACTION
Tensor
typmani
Cartilaginous
part of ET, its
own bony
canal
Upper part of
handle of
malleus
Branch from
mandibular
nerve [V3]
tensing
tympanic
membrane to
reduce the
force of
vibrations in
response to
loud noises
Muscles of the middle ear

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Stapedius pyramidal
eminence
Neck of
stapes
Branch of
facial nerve
[VII]
pulls the
stapes
posteriorly
and prevents
excessive
oscillation in
loud noises

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THE CHORDA TYMPANI NERVE
 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.

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THE TYMPANIC PLEXUS
 It is formed by the
– tympanic branch of the glossopharyngeal nerve
(Jacobson's nerve) and
– 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.

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Mastoid air cells
• Mastoid processes
can be pneumatic,
sclerosed or mixed
• Mastoid process
develops by the age
of 2 yrs
• Antrum is well
developed at birth
• Aditus ad antrum is
the opening in the
posterior wall of
middle ear and leads
posteriorly to antrum
• Vary considerably in number, form & size
• Interconnected & lined by squamous non-ciliated
epithelium

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Mastoid antrum
• The lateral:
formed by squamous
temporal bone
• Medial wall:
related with the posterior
and horizontal semicircular canal
• Posteriorly :
communicate by several
openings with mastoid air cells.
Important surgical marks to
mastoid antrum is the
MacEwen’s Triangle
• The roof of mastoid antrum (tegmin antri) separate
it from middle cranial fossa.

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MacEwen’s Triangle
• Superior: temporal line
• Anterior: postero-superior
margin of bony external
auditory canal opening
• Posterior: tangent drawn to
mid-point of posterior wall
of external auditory canal
• Contains spine of Henle
• Mastoid antrum lies 12-15
mm deep to triangle

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Mucosa Of Middle Ear Cleft
• Mucus membrane of the nasopharynx is
continuous with that of middle ear ,aditus and
antrum.
• Mucus secreting
• Respiratory type
• Cilia bearing
• Lines the bony wall of the tympanic cavity
and wraps the middle ear structure_ossicles
,muscles ligaments and nerves like
peritoneum wraps viscera of the abdomen.

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Blood supply
• Arteries :
Middle ear is supplied by the following
1)Two main arteries
a)Anterior tympanic branch of maxillary artery
b)Stylomastoid branch of posterior auricular artery
2)Four minor arteries
a)Petrosal branch of middle meningeal artery
b)Superior tympanic branch of middle meningeal artery
c)Branch of artery of pterygoid canal
d)Tympanic branch of internal carotid
• Veins :
Pterygoid venous plexus
Superior petrosal sinus

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Lymphatic drainage
• Middle ear :
Retropharyngeal & parotid nodes
• ET :
Retropharyngeal group of nodes

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Facial Nerve

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• Meatal segment : 8-10 mm
• Labyrinthine segment : 4 mm
• Tympanic segment : 11 mm
• Mastoid segment : 13 mm

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• Gives 3 branches
in intratemporal
part.
1. Greater
petrosal
nerve
2. Nerve to the
stapedius
3. Chorda
tympani

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Surgical landmarks of facial nerve
• Processus cochleariformis
• Oval window and horizontal canal
• Short process of the incus
• Pyramid
• Digastric ridge: just deep to or medial to
the mastoid tip anterior to that is the tip of
the facial nerve

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• Cartilaginous pointer: sharp traingular
piece of cartillage of pinna and points to
the nerve which lies 1 cm deep .

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