ANATOMY OF THE MIDDLE EAR

Dr. Mudasir-ul-islamPostgraduate presentation

Government Medical CollegeSrinagar, Kashmir. Oct. 2010.

Overview Embryology Walls of middle ear Contents of middle ear Spaces of middle ear Blood supply of middle ear Endoscopic pictures

Anatomy of middle ear

Tubotympanic recess Proximal part Distal part Malleus and incus Stapes Tensor tympani Stapedius Ligament of malleus Tympanic membrane

Embryology

Malformed ossicles Fused stapes Facial nerve Stapedial artery

Anomalies

Divisions of middle ear

• Mesotympanum– Facial recess– Sinus tympani

• Hypotympanum• Epitympanum

Lateral Medial Floor Roof Anterior Posterior

Walls of middle ear

Bony epitympanum Tympanic membrane Hypotympanum

Lateral wall

Lateral wall

Tympanic membrane viewed from middle ear

Ct temporal bone coronal cut

Chorda tympani..enters medial surface of fissure through separate canaliculus (canal of Huguier) runs posterior then to fibrous and mucosal layers, across upper part of handle of malleus, along the membrane but below the level of posterior malleolar fold

Then enters the posterior canaliculus obliquely and medially downward,through the posterior wall of tympanic cavity to reach facial nerve

Chorda tympani

During cortical mastoidectomy the fibrous strands of tympanomastoid suture can often be confused with corda tympani although the angle of white strands of suture lines different from angle of corda

Cont…

Middle ear view

Tegmen tympani..both petrous andsquamous portion of temporal bone form it

Petrosquamous suture,as it does not close till adult life,can lead to infection in extradural space in children

Veins..superior petrosal sinus

Roof of middle ear

Ct temporal bone coronal cut

Compact or pneumatised bone Separates the hypotympanum from the dome

of jugular bulb Thickness varies floor may be deficient..here jugular bulb is

covered by fibrous tissue and mucous membrane

At the Junction of floor and medial wall tympanic branch of 9th nerve opens into middle ear from origin below the base of skull.

Floor of the middle ear

Lower one third thin plate of bone covering carotid artery perforated by sup and inf

caroticotympanic nerves

Middle one third orifice of Eustachian tube above this opening is canal for tensor

tympani muscle

Anterior wall of middle ear

Upper one third anterior epitympanic recess small niche anterior to ossicular head can hide residual Cholesteatoma in

canal wall up surgery

Contd….

Ct temporal bone

Promontory Oval window Round window niche Facial nerve canal

Medial wall of middle ear

Covers part of the basal part of cochlea Contains nerves forming tympanic plexus Tympanic branch of ninth nerve may be

covered by bone forming a small canal

Promontory

Medial wall of mesotympanium after removal of TM

Behind and above the oval window

Kidney shaped

Connects tympanic cavity with the vestibule closed by stapes footplate and annular ligament

Size 3.25×1.75

Oval 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

Round window niche

Medial wall of tympanic cavity

Facial nerve canal,also called fallopain canal Runs above promontory and oval window in

anterosuperior direction Smooth rounded lateral surface has

microdehiscenses Along the line of nerve two or three blood

vessels are visible(straight) This canal is marked anteriorly by processus

cochleariformis and behind by the oval window

Facial nerve canal

Processus cochleariformis is a curved piece of bone housing tensor tympani muscle tendon

Behind the oval window facial canal starts inferiorly

….

Cont.

Facial nerve course

Ct temporal bone coronal cut

Aditus and antrum Fossa incudus Pyramid Canal within the pyramid curves downwards

and backwards to join descending portion of facial nerve canal

Posterior wall of middle ear

Coronal section at long process of incus

Groove between pyramid facial nerve and annulus of tympanic membrane

Shallow lower down Medially is facial nerve Laterally tympanic annulus Corda tympani running obliquely through

wall between the two Posterior tympanotomy

Facial recess

Posterior extent of mesotympanum Lies deep to promontory and facial nerveMost inaccessible siteCholesteatoma in posterior wall is difficult to

eradicateWorst region to access is above the pyramid

posterior to intact stapes and medial to facial nerve

Retrofacial appraoch not possible because posterior SCC blocks access

Sinus tympani

Endoscopic view of posterior medial wall of tympanic cavity

Ct temporal bone axial cut

OssiclesMusclesChorda tympaniTypanic plexus ligamentsAir

Contents of middle ear

Ossicular transmission

…

ossicles

Ossicles

Ossicles

• Malleus (hammer)

• Incus (anvil)

• Stapes (stirrup) smallest bone of the body

Malleus Largest 9mm in length Head in epitympanum Suspended by superior malleal ligament Saddle shaped facet on posteromedial

surface Articulates with the incus..a synovial joint

ossicles

Below neck is the lateral and anterior process of malleus

Lateral process receives ant and post folds from tympanic annulus

Handle downwards medially and backwards Between mucosal and fibrous layer Closely attached to membrane at lower

end fine web of mucosa ossicular reconstruction

Contd…

Body Two processes Short process Long process Lenticular process

Incus

Head Neck Ant and posterior crus Foot plate

Stapes

Head Points laterallyStapedius tendon gets inserted over the post

part of neck and upper portion of post crusCrura arises from broader lower part of neck

and ant crus is thinner and less curved than the post one

Contd….

Foot plate Convex superior margin Almost straight inferior margin Curved ant and post ends Long axis is horizontal and post end slightly

lower than the anterior 3cm long 1.4mm wide Sesamoid bone ..fourth ossicle

Contd…

Blood supply

Blood supply

Blood supply

Stapedius Origin..wall of conical cavity within the

pyramid and from downward curved continuation of this canal in front of descending portion of facial canal

Supplied by small branch of facial nerve

Muscles of the midlle ear

Tensor tympani

Origin is wall of bony canal above eustachain tube,cartilaginous portion of tube, greater wing of sphenoid

Passes backward into tympanic cavity,along medial wall little below facial nerve

Enters processus cochlearformis held by transverse tendon latertally

Medial aspect of malleus head Supplied by mandibular nerve via branch

from medial pterygoid nerve

Tensor tympani muscle

Tensor tympani

Inserts on the malleus and acts to tense thetympanic membrane reducing theeffectiveness of sound transmission, protectingthe inner ear during loud sounds.

Innervation from a branch of the mandibularnerve (V3 of CN V).

Contd…

Tensor tymapni

Tympanic branch of 9th nerve,also called jacobson’s nerve

Caroticotympanic nerves Supplies mucosal layer of TM……

Tympanic plexus

Lagaments of middle ear

ligaments

Mucus secreting Respiratory type Cilia bearing Three distint mucociliary pathways Epitympanic Promontarial Hypotympanic(largest) These pathways coalesce at tympanic

orifice of eustachain tube

MUCOSA OF MIDDLE EAR

Mucosa covers ossicles and tendons Ventilation of epitympanic space… Ant and post istmic tympani Prussack’s space

Cont…

Length 45 degrees forwards and medially Bony and cartilaginous parts Mucosa

Eustachian tube

Length Isthmus Relation with tensor tympani Relation with carotid canal Cross section

Bony part

Length Medial and lateral cartilage Fixed to base of skull between petrous part

and greater wing of sphenoid Ends at root of medial pterygoid plate Back Front Apex

Cartilaginous part

S.No

BRANCH PARENT ARTERY REGION SUPPLIED

1 ANT TYMPANIC

MAXILLARY TM,MALLEUS,INCUS,ANT TYMPANIC CAVITY

2 STYLOMASTOID

POST AURICULAR POST PART OF TYMPANIC CAVITY,STAPEDIUS MUSCLE

3 MASTOID STYLOMASTOID MASTOID AIR CELLS

4 PETROSAL MIDDLE MENINGEAL

ROOF OF MASTOID AND ROOF OF EPITYMPANUM

5 SUP TYMPANIC

MIDDLE MENINGEAL

MALLEUS ,INCUS, TENSOR TYMPANI

6 INF TYMPANIC ASCENDING PHARYNGEAL

MESOTYMPANUM

7 BRANCH ARTERY OF PTERYGOID CANAL

MESO AND HYPOTYMPANUM

8 TYMPANIC ARCHES

INTERNAL CAROTID

MESO AND HYPOTYMPANUM

Blood supply of middle ear

Anatomic Considerations

• Epitympanum– Above short process

of malleus– Contains head of

malleus, body of incus and associated ligaments and mucosal folds

– Pars flaccida lacks support from a fibrous middle layer

Anatomic Considerations

• Epitympanic cholesteatoma patterns of spread from Prussack’s space– Posterior

epitympanum– Posterior

mesotympanum– Anterior

epitympanum

Cholesteatoma spread

• Posterior epitympanum – through superior incudal space to mastoid antrum

Cholesteatoma spread

– Posterior mesotympanum – inferiorly through posterior pouch of von Troeltsch to stapes, round window, sinus tympani and facial recess

Cholesteatoma spread

• Anterior epitympanum – anterior to head of malleus, may gain access to supratubal recess via anterior pouch of von Troeltsch

Thank You