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middle ear anatomy
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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