Middle ear anatomy raju 1 (2) final 1
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Transcript of 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
`
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
Thank You