middle ear anatomy raju 1 (2) final 1

DR. RAJU MANDALJUNIOR RESIDENT

DEPARTMENT OF ENTMEDICAL COLLEGE, KOLKATA

WHAT IS MIDDLE EAR?

Conventionally, the ear has been divided into three parts:

1. External Ear

2. Middle Ear

3. Internal Ear

THE MIDDLE EAR CLEFT

The middle ear cleft consists of:

1. Tympanic cavity

2. Eustachian tube

3. Mastoid air cell system

THE TYMPANIC CAVITY

It can be divided into three parts-

• Epitympanum- Lies above level of the malleolar fold.

It contains- head of the malleolus, body of the incus,ossicular ligaments & mucosal fold.

• Mesotympanum-Lies opposite the pars tensa of tympanic cavity.

It contains- long process of incus stapes, mucosal folds

• Hypotympanum-Lies below the level of inferior part of tympanic sulcus.

It contains-glomus body and bulge of jugular bulb.

THE TYMPANIC CAVITY

It is like a six sided box –1. Roof (Tegmental wall)

2. Floor (jugular wall)

3. Lateral wall(Membranous wall)

4. Medial wall (Labyrinthine wall)

5. Posterior wall (Mastoid wall )

6. Anterior wall(Carotid wall)

R00F OF TYMPANIC CAVITY

Formed by tegmen tympani ( both petrous and squamous ) which separates the middle ear space from the middle cranial fossa

Veins to superior petrosl sinus passes through petrosquamous suture

This suture line not closed till adult life, so is a route of infection into extradural space in children.

FLOOR OF TYMPANIC CAVITY

It is formed by pneumatisedbone, or may be deficient when covered by muscle or mucous membrane

It separates from jugular bulb

At the junction of floor and

medial wall of the cavity a small opening present

Its passes tympanic branch of

glossopharyngeal nerve

LATERAlWALL OF TYMPANIC CAVITY

It is formed by-

Superiorly-bony lateral wall of

epitympanum

Centrally-tympanic mmbrane

Inferiorly-bony lateral wall of

hypotympanum

LATERAL WALL OF TYMPANIC CAVITY

Lateral epitympanic wall- Wedged shaped Sharped inferior portion called

scutum, which is very thin &easily eroded by choleteotoma.

Petrotympnic fissure-

Open anteriorly just above

attachment of tympanic

membrane. Its-

receives anterior malleolarligament Transmit anterior tympanic branchof maxillay artery

LATERAL WALL OF TYMPANIC CAVITY

Chorda tympani nerve-

Enters through anterior canaliculus Runs posteriorly between the

fibrous and mucosal layers of tympanic membrane

Enters posterior canaliculus Runs obliquely downwards and

medially through the posteriorwall to reach facial nerve Point of entry to facial nerve is

variable, usually inferior 1\3 rd of facial canal in ant surface

ANTERRIOR WALL OF TYMPANIC CAVITY

Lower third-

Consists of thin bone covering

internal carotid artery

It is perforated by sup.& inf.

corticotympanic nerve carrying

sympathetic fibres to tympanic

plexux from internal carotid

artery

ANTERIOR WALL OF TYMPANIC CAVITY

Middle third-Comprise tympanic opening of theEustachian tube(5mm*2mm)

Upper third-canal containing the tensor tympani

muscleSmall niche anterior to ossicularhead called anterior epitympanicsinus-which can hide residual cholesteotoma

MEDIAL WALL OF TYMPANIC CAVITY

Central portion occupied by a

rounded elevation- called

promontory.

A small Groove over it contains

tympanic plexus

MEDIAL WALL OF TYMPANIC CAVITY

Behind & above the promontory, lies ovalwindow.

Oval window connects

tympanic cavity with vestibule.But it is closed by foot plate of stapes

It is kidney shaped(3.25 mm long & 1.75 mm wide)

MEDIAL WALL OF TYMPANIC CAVITY

The round window is triangular in shape

It has Ant., Post-Sup, & Post-Inf wall

about 2.3*1.9 mm size

Separated from scalatympani by secondary tympanic membrane

MEDIAL WALL OF TYMPANIC CAVITY

Posterior extension of promontory-Subiculum

Post-Sup & Post-Inf walls of round window meets posteriorly & forms-Sinus Tympani

It is most inaccessible part of middle ear & mastoid

MEDIAL WALL OF TYMPANIC CAVITY

Fallopian canal or facial canal runs above promontory and oval window in an antero-posterior direction.

Anterior most part of the canal is processus cochleariformis which attached to tendon of tensor tympani muscle

Behind the oval window, the facial canal starts to turn inferiorly as it begins to descent in the posterior wall

Smooth lateral surface of facial canal may have microdehicense, which diagnosed by visibility of some straight blood vessel over canal

Above processus cocleaformisa small swelling corresponds to genuculate ganglion

More posteriorly facial nerve related to lateral semicircular canal

During cortical mastoidectomythe triangular realationship between lat semicircular canal,short process of incuss &facial nerve is very helpful

POSTERIOR WALL OF TYMPANIC CAVITY

Upper part has a irregular opening-aditus of antrum

Below the aditus is the Fossa incuidis-which houses short process of incus and its suspensory ligament

Below fossa incuidis ,a conical projection called Pyramid-attached to stapedius muscle & tendon

POSTERIOR WALL OF TYMPANIC CAVITY

Facial recess- bounded medially by the facial nerve and laterally by the tympanic annulus

It allows posterior tympanotomy

POSTERIOR WALL OF TYMPANIC CAVITY

Posterior extension of mesotympanum deep to facial nerve and promontory –called Sinus Tympani

Cholesteotoma from this space is extremely difficult to eradicate

CONTENTS OF THE TYMPANIC CAVITY

The ear ossicles & their ligaments- Malleus, Incus and Stapes

The muscles- Stapedius and Tensor Tympani

Nerves-Chorda Tympani and Tympanic plexus

OSSICLES OF TYMPANIC CAVITY

CONTENTS OF THE TYMPANIC CAVITY MALLEUS > Largest ossicles- length about

9 mm Three parts- head, neck &

handle or manubrium Head lies in the

epitympanum.Head has a facet on postero medial surface for articulation with body of the incus

Handle runs downwards, medially and slightly backwards between the mucous and fibrous layers of TM

CONTENTS OF THE TYMPANIC CAVITY

From the anterior process, a slender anterior ligament arises to insert into the petrotympanic fissure

Lateral process receives the anterior and posterior malleolar fold

The tendon of the tensor tympani is inserted into a small projection on the medial surface of the handle

CONTENTS OF THE TYMPANIC CAVITY INCUS>

• It has three parts-Body,Short process & Long process

• Body has a facet to articulate with malleus.Body is suspended by superior incuidal ligament that is attached to tegmentympani.

CONTENTS OF THE TYMPANIC CAVITY INCUS>• Short process projects backwards

in the fossa incudis to which it is attached by short suspensoryligament

• Long process projects in mesotympanum medial to HOM.

• At tip of Long process , lenticularprocess present( fourth ossciles) which articulate with head of stapes.

CONTENTS OF THE TYMPANIC CAVITY

STAPES>• Two crura arise from the neck

and join the footplate

• The footplate is about 3 mm long and 1.4 mm wide; it lies in the oval window where it attached to the bony margin by the annular ligament

• Head articulates with the lenticular process of incus

• Stapedius tendon inserts into the neck and posterior crus

Ligaments of middle ear

CONTENTS OF THE TYMPANIC CAVITYMUSCLES>

The stapedius muscles-

Arises from the walls of the conical cavity within the pyramid and insert into the stapes.

Supplied by a branch of the facial nerve .

The tensor Tympani-Arises from the walls of the bony canal lying above the ET, cartilegenous portion of the ET & the greater wings of the sphenoid

Turns at processuscochleaformis

Inserts at handle of the malleus

Supplied by branch of mandibular nerve

MUCOSA>

HISTOLOGICALLY-

1. ET- lined by cilliated columner epithelium.Incartilajenous part pseudostratifiedcolumnar and in bony part several mucous gland in submucosa present

2. Tympanic cavity-cilliated columner in anterir& inferior part and cuboidal in posterior part

3. Epitympanum and mastoid air cells- by flat non cilliated epithelium

Three distinct mucocillary pathway present-Epitympanic, Promonterial, and Hypotympanic, the latter is the largest

Each coalesces at the tympanic orrifice of ET

MUCOSAL FOLDS>• Like peritoneum in abdomen it covers

ossicles,their ligaments,muscles, tendons in middle ear cavity

• It carry blood supply to &from contents of middle ear

These folds separates middle ear in compartments-As a result only route for ventilation from epitympanic space to mesotympanum is small opening between various mucous fold-Anterior & Posterior isthmus tympani.

MUCOUS FOLD>

Described by PROCTOR

BLLOD SUPPLY OF THE TYMPANIC CAVITY 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)some 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

d) Inferior tympanic branch of ascending

pharyngeal artery.

Blood supply

NERVE SUPPLY OF MIDDLE EAR

It is by tympanic plexus which 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 petrosalnerve that contains all the parasympathetic fibres of the glossopharyngeal nerve

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MUCOUS FOLD>PRUSSAKS SPACE-Bounded by-1. Laterally-Pars flaccida2. Medially-neck of the malleus3. Above-anterior malleolar ligament4. Below-short process of the malleus

This place can play an important role in the retention of the keratin and subsequent devolopment of cholesteotoma.

EUSTACHIAN TUBE

Links middle ear with nasopharynx.

Length 36 mm.

Lateral bony segment – 12 mm.

Medial cartilagenous segment – 24 mm.

Narrowest portion is the Isthmus.

Caroid artery and the Tensor tympani muscle are separated from the tube by thin plates of bones.

Opens in the nasopharynx behind and below the posterior end of inferior turbinate.

Behind the torus is the fossa of Rosenmuller

The Mastoid Air Cell System

Mastoid can be Well pneumatised Diploetic Sclerotic

Honeycomb of air cells Divided into many

groups as per theiranatomical location

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