middle ear anatomy

1. Dr. Mudasir-ul-islam
Postgraduate presentation
Government Medical College
Srinagar, Kashmir. Oct. 2010.

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

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

8.  Malformed ossicles
 Fused stapes
 Facial nerve
 Stapedial artery

9. • Mesotympanum
– Facial recess
– Sinus tympani
• Hypotympanum
• Epitympanum

10.  Lateral
 Medial
 Floor
 Roof
 Anterior
 Posterior

11.  Bony epitympanum
 Tympanic membrane
 Hypotympanum

15.  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

16.  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

18.  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

20.  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.

21. 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

22.  Upper one third
anterior epitympanic recess
small niche anterior to ossicular head
can hide residual Cholesteatoma in canal
wall up surgery

25.  Promontory
 Oval window
 Round window niche
 Facial nerve canal

27.  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

29. 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

30.  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

32.  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

33.  Processus cochleariformis is a curved piece of
bone housing tensor tympani muscle tendon
 Behind the oval window facial canal starts
inferiorly
 ….

36.  Aditus and antrum
 Fossa incudus
 Pyramid
 Canal within the pyramid curves downwards
and backwards to join descending portion of
facial nerve canal

38.  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

39. 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

43. Ossicles
Muscles
Chorda tympani
Typanic plexus
ligaments
Air

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

56.  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

57.  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

58.  Body
 Two processes
 Short process
 Long process
 Lenticular process

59.  Head
 Neck
 Ant and posterior crus
 Foot plate

60.  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

61.  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

65.  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

68.  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

69. 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).

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

75.  Mucus secreting
 Respiratory type
 Cilia bearing
 Three distint mucociliary pathways
 Epitympanic
 Promontarial
 Hypotympanic(largest)
 These pathways coalesce at tympanic orifice
of eustachain tube

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

77.  Length
 45 degrees forwards and medially
 Bony and cartilaginous parts
 Mucosa

78.  Length
 Isthmus
 Relation with tensor tympani
 Relation with carotid canal
 Cross section

79.  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

80. S.No BRANCH PARENT ARTERY REGION SUPPLIED
1 ANT
TYMPANIC
MAXILLARY TM,MALLEUS,INCUS,ANT
TYMPANIC CAVITY
2 STYLOMASTOI
D
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

81. 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

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

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

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

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