Anatomy of middle ear

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Presentation Transcript

Anatomy of middle ear : 

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


Embryology : 

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

Anomalies : 

Malformed ossicles Fused stapes Facial nerve Stapedial artery Anomalies

Divisions of middle ear : 

Divisions of middle ear Mesotympanum Facial recess Sinus tympani Hypotympanum Epitympanum

Walls of middle ear : 

Lateral Medial Floor Roof Anterior Posterior Walls of middle ear

Lateral wall : 

Bony epitympanum Tympanic membrane Hypotympanum Lateral wall

Lateral wall : 

Lateral wall

Tympanic membrane viewed from middle ear : 

Tympanic membrane viewed from middle ear

Ct temporal bone coronal cut : 

Ct temporal bone coronal cut

Chorda tympani : 

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

Cont… : 

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 : 

Middle ear view

Roof of middle ear : 

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 : 

Ct temporal bone coronal cut

Floor of the middle ear : 

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

Anterior wall of 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

Contd…. : 

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 : 

Ct temporal bone

Medial wall of middle ear : 

Promontory Oval window Round window niche Facial nerve canal Medial wall of middle ear

Promontory : 

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 : 

Medial wall of mesotympanium after removal of TM

Oval window : 

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

Round window niche : 

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 : 

Medial wall of tympanic cavity

Facial nerve canal : 

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

Cont. : 

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 : 

Facial nerve course

Ct temporal bone coronal cut : 

Ct temporal bone coronal cut

Posterior wall of middle ear : 

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 : 

Coronal section at long process of incus

Facial recess : 

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

Sinus tympani : 

Posterior extent of mesotympanum Lies deep to promontory and facial nerve Most inaccessible site Cholesteatoma in posterior wall is difficult to eradicate Worst 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 : 

Endoscopic view of posterior medial wall of tympanic cavity

Ct temporal bone axial cut : 

Ct temporal bone axial cut

Contents of middle ear : 

Ossicles Muscles Chorda tympani Typanic plexus ligaments Air Contents of middle ear

Ossicular transmission : 

Ossicular transmission

… : 


ossicles : 

ossicles

Ossicles : 

Ossicles

Slide 48: 

Ossicles Malleus (hammer) Incus (anvil) Stapes (stirrup) smallest bone of the body

ossicles : 

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

Contd… : 

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…

Incus : 

Body Two processes Short process Long process Lenticular process Incus

Stapes : 

Head Neck Ant and posterior crus Foot plate Stapes

Contd…. : 

Head Points laterally Stapedius tendon gets inserted over the post part of neck and upper portion of post crus Crura arises from broader lower part of neck and ant crus is thinner and less curved than the post one Contd….

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 : 

Blood supply

Blood supply : 

Blood supply

Muscles of the midlle ear : 

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 : 

Tensor tympani

Tensor tympani muscle : 

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

Slide 68: 

Tensor tympani Inserts on the malleus and acts to tense the tympanic membrane reducing the effectiveness of sound transmission, protecting the inner ear during loud sounds. Innervation from a branch of the mandibular nerve (V3 of CN V).

Contd… : 

Contd…

Tensor tymapni : 

Tensor tymapni

Tympanic plexus : 

Tympanic branch of 9th nerve,also called jacobson’s nerve Caroticotympanic nerves Supplies mucosal layer of TM…… Tympanic plexus

Lagaments of middle ear : 

Lagaments of middle ear

ligaments : 

ligaments

MUCOSA OF MIDDLE EAR : 

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

Cont… : 

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

Eustachian tube : 

Length 45 degrees forwards and medially Bony and cartilaginous parts Mucosa Eustachian tube

Bony part : 

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

Cartilaginous 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

Blood supply of middle ear : 

Blood supply of middle ear

Slide 80: 

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

Slide 81: 

Anatomic Considerations Epitympanic cholesteatoma patterns of spread from Prussack’s space Posterior epitympanum Posterior mesotympanum Anterior epitympanum

Slide 82: 

Cholesteatoma spread Posterior epitympanum – through superior incudal space to mastoid antrum

Slide 83: 

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

Slide 84: 

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

Thank You : 

Thank You