Middle ear anatomy

1. MIDDLE EAR ANATOMY
and
EUSTACHIAN TUBE FUNCTION TEST
Dr. YASHI JARIYA

2. • The middle ear cleft consists of the
□ Tympanic cavity,
□ Eustachian tube and
□ Mastoid air cell system.
• The tympanic cavity is a irregular, air-filled space within the
temporal bone between the tympanic membrane laterally and
the osseous labyrinth medially.
• It contains the ossicles, muscles and structures, like the
tympanic segment of the facial nerve

4. THE TYMPANIC CAVITY
• Divided into three compartments
• The epitympanum (upper),
• The mesotympanum (middle) and
• Hypotympanum (lower).
• The epitympanum or attic, lies above the level of malleolar
folds and is separated from the mesotympanum and
hypotympanum by a series of mucosal membranes and folds.
• The mesotympanum lies opposite the tympanic membrane.
• The hypotympanum lies below the level of the inferior part of
the tympanic sulcus and is continuous with the
mesotympanum above.

6. THE LATERAL WALL
• The lateral wall of the tympanic cavity is
formed by the
• Bony lateral wall of the epitympanum superiorly,
• Tympanic membrane centrally and
• Bony lateral wall of the hypotympanum inferiorly.
• The lateral epitympanic wall is wedge-shaped
in section and its shape inferior portion is also
called the outer attic wall or scutum.

7. • Present in the bone of the medial surface of the lateral
wall of tympanic cavity.
• The petrotympanic fissure (also known as the
squamotympanic fissure) is a fissure in the temporal
bone that runs from the temporomandibular joint to
the tympanic cavity.
• The petrotympanic fissure is 2 mm long which opens
anteriorly just above the attachment of the tympanic
membrane.
• It receives the anterior malleolar ligament and
transmits the anterior tympanic branch of the
maxillary artery which supplies the tympanic
membrane.

8. THE ROOF
• The roof of the epitympanum is the tegmen tympani
• It is a thin bony plate that separates the middle ear
space from the middle cranial fossa.
• It is formed by both the petrous and squamous
portions of the temporal bone.
• The petrosquamous suture line, which does not close
until adult life, can provide a route of access for
infection into the extradural space in children.
• Veins from the tympanic cavity running to the superior
petrosal sinus pass through this suture line.

9. THE FLOOR
• The floor of the tympanic cavity separates the
hypotympanum from the dome of jugular bulb.
• Its thickness varies according to the height of the
jugular fossa.
• Occasionally, the floor is deficient and the jugular
bulb is then covered only by fibrous tissue and a
mucous membrane.
• At the junction of the floor and the medial wall of
the cavity there is a small opening that allows the
entry of the tympanic branch of the
glossopharyngeal nerve into the middle ear.

11. MEDIAL WALL
• Promontory
• Oval window
• Round window
• Tympanic part of bony facial nerve canal
• Lateral semicircular canal
• Processus cochlearformis

12. ● The promontory
is a rounded
elevation
occupying much
of the central
portion of the
medial wall.
● Formed by basal
turn of cochlea.
● usually has small
grooves on its
surface containing
the nerves which
form the tympanic
plexus.

13. OVAL WINDOW
● lies Behind and above the promontory
● Akidney-shaped openingthat connects
the tympanic cavity with the vestibule.
● Close by a footplate of the stapes.
● Its size average 3.25 mm long and
mm wide.
1.75

15. ROUND 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
• RWN is 2.3mm×1.9mm and is
placed at right angles to plane
of stapes foot plate

16. FACIAL NERVE CANAL
• The facial nerve canal (or Fallopian canal)
runs above the promontory and oval window in
an anteroposterior direction.
• The facial nerve canal is marked anteriorly by
the processus cochleariformis, a curved
projection of bone, concave anteriorly, which
houses the tendon of the tensor tympani
muscle as it turns laterally to the handle of the
malleus.
• The region above the level of the facial nerve
canal forms the medial wall of the epitympanum.
• Behind the oval window, the facial canal starts
to turn inferiorly as it begins its descent in the
posterior wall of the tympanic cavity.

18. • The dome of the lateral semicircular canal is
the major feature of the posterior portion of the
epitympanum, lying posterior and extending a
little lateral to the facial canal

19. • The facial nerve canal (or Fallopian canal) runs above the
promontory and oval window in an anteroposterior direction.
• It has a smooth rounded lateral surface that often has
microdehiscences
• When the bone is thin or the nerve exposed by disease, there are
two or three straight blood vessels clearly visible along this line of
nerve.
• These are the only straight blood vessels in the middle ear and
indicate that the facial nerve is very close by.
• The facial nerve canal is marked anteriorly by the processus
cochleariformis, a curved projection of bone, concave anteriorly,
which houses the tendon of the tensor tympani muscle as it turns
laterally to the handle of the malleus.
• Behind the oval window, the facial canal starts to turn inferiorly as
it begins its descent in the posterior wall of the tymapnic cavity.

20. • The region above the level of the facial nerve canal
forms the medial wall of the epitympanum.
• The dome of the lateral semicircular canal is the major
feature of the posterior portion of the epitympanum,
lying posterior and extending a little lateral to the
facial canal.
▪In front and a little below this, above the processus
cochleariformis, may be a slight swelling
corresponding to the geniculate ganglion, with the
bony canal of the greater superficial petrosal nerve
running for a short distance anteriorly.

22. THE POSTERIOR WALL
• The posterior wall is wider above than below.
• Upper part a large irregular opening – the aditus ad antrum, that
leads back from the posterior epitympanum into the mastoid
antrum.
• Below the aditus is a small depression, the fossa incudis, which
houses the short process of the incus and its suspensory ligament.
• Below the fossa incudis and medial to the opening of the chorda
tympani nerve is the facial recess.
• The pyramid, a small hollow conical projection with its apex
pointing anteriorly.
• This house the stapedius muscle and tendon, which inserts into
the posterior aspect of the head of stapes.
• The canal within the pyramid curves downwards and backwards to
join the descending portion of the facial nerve canal.

24. FACIAL RECESS
●The facial recess is a groove which lies between the pyramid with facial
nerve, and the annulus of the tympanic membrane .
● The facial recess is bounded:
– Medially by the
facial nerve and
– Laterally by the tympanic
• annulus,
– with the chorda
tympani nerve
running obliquely
through the wall
between the two.
• The chorda always runs medial to the tympanic
membrane.

25. FACIAL RECESS
• The angle between the facial nerve and the
chorda allows a posterior tympanotomy,
allowing access to the middle ear from the
mastoid without disruption the tympanic
membrane.

26. SINUS TYMPANI
•Boundaries:
– Superior: Ponticulus
– Inferior: Subiculum
– Lateral: Mastoid
Segment of Facial
Nerve
– Medial: Posterior
semicircular canal
• It evades direct surgical
visualization during surgery.
Site for cholesteatoma
recurrence

27. • The sinus tympani is a posterior extension of the mesotympanum
and lies deep to both the promontary and the facial nerve.
• This extension of air cells into the posterior wall can be extensive,
and is probably the most inaccessible site in the middle ear and
mastoid.
• The sinus can extend as far as 9 mm into the mastoid bone when
measured from the tip of the pyramid.
• The medial wall of the sinus tympani becomes continuous with the
posterior portion of the tympani cavity where it is related to the
oval and round window niches and the subiculum of the
promontory.
• On rare occasions it can communicate with the mastoid air cells.

28. Contents of middle ear cavity
• Air
• 3 ossicles : malleus, incus and stapes
• 2 muscles : tensor tympani & stapedius
• nerves : chorda tympani & tympanic
plexus
• Mucosal folds & ligaments
• Blood vessels

29. THE MALLEUS
• Largest of the three ossicles - 9mm length
• It Has Head, Neck,Anterior and Lateral Process,
• Handle
o Suspended by the superior ligament between head and
• the tegmen tympani.
• Head has saddle - shaped facet on its
posteromedial surface
o to articulate with the body of the incus

30. Head
Neck
Anterior
Process
Handle
Lateral
Process

31. THE INCUS
• It has a Body, Short Process and a long process and
• a lenticular process
• body of the incus
o is suspended by the superior incudal ligament that is
• attached to the tegmen tympani.
• Long process
o extends downwards behind the handle of malleus
o articulates with the head of the stapes by its lenticular
• process.

32. • Short process
o Lodges in the fossa incudis
• Lenticular process
o Sometimes been called the fourth ossicle because of its
• incomplete fusion with the tip of the long process

33. Body
Short
Process
Facet
Long
Process
Lenticular
Process

34. THE STAPES
• Shaped like a stirrup
• Consists of a head, neck, the anterior and
posterior crura and a footplate.
• The Head points laterally and has a small
cartilage- covered depression for a synovial
articulation with the lenticular process of the
incus
• The foot plate directs medially and closes the
Oval window.
• Stapedius tendon inserts into the posterior
part of the neck and upper portion of the
posterior crus.

35. Anterior Crus
Head
Neck
Foot Plate
Posterior
Crus

36. canal
MUSCLE ORIGIN INSERTION NERVE
SUPPL
Y
ACTION
Tensor
typmani
Cartilaginous
part of ET, its
own bony
Upper part of
handle of
malleus
Branch from
mandibular
nerve [V3]
tensing
tympanic
membrane to
reduce the
force of
vibrations in
response to
loud noises
MUSCLES OF THE MIDDLE EAR

37. Stapedius pyramidal
eminence
Neck of
stapes
Branch of
facial nerve
[VII]
pulls the
stapes
posteriorly
and prevents
excessive
oscillation in
loud noises

38. THE CHORDATYMPANI NERVE
.
• It enters the tympanic cavity from the
posterior canaliculus at the junction of the
lateral and posterior walls.
• It runs across the medial surface of the
tympanic membrane between the
mucosal and fibrous layers.
• Then passes medial to the upper portion of
the handle of the malleus above the tendon
of tensor tympani.
• Continues forwards and leaves by way of
the anterior canaliculus, which
subsequently joins the petrotympanic
fissure.

39. ▪The chorda tympanic nerve leaves the medial
surface of the petrotympanic fissure through a
separate anterior canaliculus (canal of
Huguier) which is sometimes confluent with
the fissure.
• The point of entry of the chorda tympani into
the facial nerve bundle is usually at the level
of the inferior third of the facial canal on its
anterior wall.
• The nerve carries taste sensation from the
anterior two-third of the same side of the
tongue and secretomotor fibres to the
submandibular gland.
•

42. THE TYMPANIC PLEXUS
• It 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 petrosal nerve that contains
all the parasympathetic fibres of the glossopharyngeal nerve.

43. Mucosal Folds of the Middle Ear

44. Mucosal Fold Development
□ Between 3rd to 7th month of fetal age , the
mesenchymal tissue of middle ear cleft is
absorbed.
□ Simultaneously the primitive tympanic cavity
develops by a growth of an endothelium-lined
fluid pouch(Tubo Tympanic Recess)
extending from the ET into the cleft.
□ The terminal end of the TTR buds out to form
4 primary sacci- saccus anticus,saccus
medius, saccus superior and saccus posticus
□ The sacci or pouches start to enlarge in the
middle ear cleft to replace the pre-existing
mesenchyme.

45. □ Walls of the pouches🡪 mucosal lining of middle
ear
□ MUCOSALfold 🡪Plane of contact between two
neighbouring pouches.

47. □ Mucosal folds extend from the
wall of middle ear to its content &
carry ligaments and blood vessels
to the ossicles.
□ Mucosal folds- two types
a) Composite fold: ligament+ lining mucosa
ex:Ant.MLF, Lat.MLF and Post. Incudal
fold
b) Duplicate fold: fusion of two expanding
air sac walls in absence of any
interposing structure. ex: tensor tympani
fold, lateral incudomalleal fold.

48. □
Important folds in middle ear:
1. Anterior malleal fold
2. Posterior malleal fold
3. Anterior malleal ligamental fold
4. Lateral malleal ligamental fold
5. Superior malleal fold
6. Superior incudal fold
7. Posterior incudal fold
8. Medial incudal fold
9. Lateral incudomalleal fold
10. Tensor tympani fold

49. Anterior Malleal Fold
❖ Origin : anterior portion neck of
malleus
❖ Insertion : anteriorly on ant.
tympanic spine
❖ Forms: medial wall of ant. Pouch of
Von Troltsch
Posterior Malleal Fold
❖ Origin : posterior portion neck of
malleus
❖ Insertion : posteriorly on post.
tympanic spine
❖ Forms: medial wall of post. Pouch of
Von Troltsch

50. Anterior Malleal Ligamental Fold
❖ Originates from neck of malleus & extends to
the anterior attic bony wall.
❖ Reflected from lateral wall of middle ear over
• Ant. Process and ligament of malleus
• ant part of chorda tympani
❖ Low posterior part is broad
and represents – ant. Limit
of Prussak’s space.

51. Lateral Malleal Ligamental Fold
□ Originates from middle portion of
the neck of malleus & attaches to
attic outer wall
□ Posteriorly confluent with ant.
Descending portion of Lat. IMF
□ Mostly complete, thick fold and
strong , so prevents progression of
pars flaccida retraction
□ Represents roof of Prussak’s space
and the floor of the lateral malleal
space

52. Superior Malleal Fold:
❖ Extends between superior surface of Malleal head
and tegmen.
❖ Contains Superior Malleal ligament.
❖ Divides upper unit of attic into anterior and posterior
parts.
Superior Incudal Fold:
❖ Extends between superior surface incudal body to
tegmen
❖ Divides posterior attic to lateral and medial part

53. d
Posterior Incudal Fold
❖ Lies between the
fibres of the post.
incudal ligament
Medial Incudal Fold
❖ Lies between the long
process of the incus
and the tendon of the
stapedial muscle upto
pyramidal eminance

54. Lateral Incudomalleal Fold
❖ Present superiorly in relation to lateral
malleal ligamental fold
❖ Divides upper lateral attic space from
the lower lateral attic space
❖ It has 2 extensions:
1. Posteriorly it horizontally extends to insert
medially onto body of the incus &
incudomalleal joint.
2. Laterally , it insert onto the medial surface
of the bony wall of scutum

55. □ Ant. Portion of the this fold bends inferiorly
towards the neck of malleus & merges with post.
portion of lat. MLF representing the post. limit of
Lat. Malleal space
□ Level is about 1mm higher than the roof of
Prussak’s space

56. Tensor Tympanic Fold
❖ Part of tympanic diaphragm
❖ Arises posteriorly from the tensor tympani
tendon
❖ Anteriorly inserts into a transverse
crest(supratubal ridge) of anterior wall of
the attic
❖ Medially insert on the bony canal of the
TTM
❖ Laterally insert on anterior malleal
ligament
❖ Separates the anterior epitympanic
recess superiorly from the supratubal
recess inferiorly

57. ❖ TTF results from fusion of saccus
anticus & anterior saccule of the
saccus medius
❖ Inclination angle of the TTF varies bet.
800 -1000 depending on the variable
growth of each saccule
❖ Determines the size of Supra
Tubal Recess and Anterior
Epitympanic Recess

58. ❖ TTF complete -total separation between ant.
epitympanum and protympanum
❖ But in majority of population TTF is incomplete.
Resulting in direct communication between ET
to ant. Epitympanic recess and then to
posterior attic. Hence prevents attic
dysventilation.

59. Tympanic Diaphragm
formed by
- Three malleal ligamental folds
- The posterior incudal fold
- The Tensor Tympani Fold
- The lateral incudomalleal fold
- Incus and Malleus
As theses components are on different level
Tympanic Diaphragm is not fully Horizontal
❖ Separates the upper unit of attic superiorly
and lower unit of attic, the Prussak’s space
inferiorly from mesotympanum

60. Tympanic Isthmus
- Attic and mastoid are isolated from
mesotympanum by Tympanic Diaphragm
- Attic aeration occurs through a 2.5 mm
opening in the tympanic diaphragm 🡪
Tympanic Isthmus
- Anteriorly - extends from tensor tympani
muscle
- Posterosuperiorly – post. Incudal ligament
- Posteroinferiorly – pyramidal eminence
- Medially – limited by attic bone
- Laterally – limited by body and short process
of incus and head of malleus

61. ❖ Tympanic isthmus divided by the medial
incudal fold into 2 portion
1. The Anterior Tympanic Isthmus
Between TTM anteriorly & the stapes posteriorly
2. The Posterior tympanic Isthmus
Between short process of incus & stapedial muscle

62. Clinical Correlation
- In long standing COM, granulation tissue and webs - block the
tympanic isthmus – failure of attic ventilation even in presence of
normal ET and well aerated mesotympanum
- This is called selective attic dysventilation
- Results in chronic attic inflammation, attic retraction pockets and
attic cholesteatoma
- Incomplete TTF allows good ventilation from the protympanic
space to anterior attic and prevents attic dysventilation even in
case of tympanic isthmus blockage
- This signifies the importance of TTF removal during surgical
treatment of middle ear disease to ensure a good ventilation of
the attic region

63. MIDDLE EAR SPACES
anterior posterior

64. THE EPITYMPANUM (ATTIC)
❖ Situated above the imaginary line passing through the
lateral process of malleus
□ Lodges the
-head and neck of malleus
-body and short process of incus
□ Boundaries
Lateral wall – shrapnell’s membrane (inf)
-scutum (sup)
Posterior wall – almost entirely by aditus
ad antrum

65. Medial wall- part of medial wall situated above
the tympanic segment of the facial nerve &
Tensor Tympani Muscle.
-it contains lateral semicircular canal
-this wall may pneumatized by
supralabrynthine tract
Posterior wall: by Aditus ad antrum
Inferiorly: Tympanic Diaphragm divides
attic into upper unit & lower unit ( Prussak”s
space)

67. Upper Unit of Attic
- Above the tympanic diaphragm
- Medially – tympanic diaphragm separates upper
unit from mesotympanum almost entirely except
at tympanic isthmus
- Laterally – tympanic diaphragm separates the
upper unit of attic from lower unit (Prussak’s
space)
- Posteriorly – communicates with mastoid cavity
through aditus

69. POSTERIOR ATTIC
- Contains mainly – post. part of the head of
malleus,
- body and short process of
incus
- Distance from tip of incus to attic roof is 6 mm
- Superior Incudal fold – sagittal plane. Divides into
-medial posterior (larger)
-lateral posterior attic (smaller)
Medial posterior attic
- Also called as Medial Incudal space
- Medially – lateral semicircular canal and fallopian
canal
- Laterally – ossicles and superior Incudal fold

70. Lateral Posterior Attic
- Narrower
- Laterally – outer attic wall
- Medially – malleus head, incus body, superior
Incudal fold
Divided into 3 spaces
1.Upper lateral attic –Superior Incudal
space,lateral Malleal space and 2.Lower lateral
attic – inferior Incudal space
▪Superior Incudal space
- Lies in a more superior position in relation to
lateral Malleal space
- Inferiorly – incudomalleal fold (separates from
inf. Incudal space)

73. Lateral Malleal space
Lies above the lateral malleal fold
Medially: malleus head & neck
Laterally: outer attic wall
Anterior : Anterior malleal fold
Posteriorly: downward turning end of
incudomalleal fold
* Superiorly opened to superior incudal space

74. Lower Lateral Attic: Inferior Incudal Space
Lies between short process and body of Incus
medially & scutum laterally
Anterior Attic or Anterior Epitympanum
❖ Anterior to the head of malleus and superior
Malleal fold
□ Cog – bony crest that extends inferiorly from
the tegmen
-superior to cochleariform process
- anterosuperior to malleus head
Divides anterior attic into
1- posterior (small) – Anterior Malleal Space
2- anterior (large) – Anterior Epitympanic
Recess

75. Anterior Malleal Space
❖ Variable size
❖ Situated between head of malleus posteriorly
and cog anteriorly

76. Anterior Epitympanic Recess
❖ Anterior epitympanic sinus/ Anterior
epitympanic space/ sinus epitympani
❖ Superiorly – Anterior part of tegmen tympani
❖ Anteriorly – Root of zygoma
❖ Posteriorly – Cog
❖ Laterally – Scutum
❖ Medially – ant. portion of the tympanic portion
of facial nerve and geniculate ganglion
❖ Floor - cochleariform process and
tensor tympani fold

77. AER is highly important in cases of
1.recurrent otorrhea with central or anterior
perforation not responding to medications
2.middle ear effusion that persists or recurs
despite repetitive myringotomies with tube
insertion
3. anterosuperiorly oriented retraction pocket
❖ In these cases if the TTF is complete – blocks
aeration of anterior epitympanum from antero-
superior mesotympanum creating
dysventilation syndrome
❖ These patients will not respond to posterior
atticotomy alone
❖ Resection of the cog and TTF is fundamental

78. Lower unit of attic (Prussak’s space)
Formed from posterior pouch of Von Troltsch as a
prolongation of Superior Saccus
Boundaries
Roof – lateral Malleal fold
Floor – neck of malleus
Anterior – anterior Malleal fold
Laterally – pars flaccida and lower edge of scutum
Posteriorly – opened to post. Pouch of Von
Troeltsch, posterior malleal fold
- Ventilation route is independent of the upper unit of
attic
- Ventilation through posterior pouch of Von Troeltsch –
rough and narrow when compared to tympanic
isthmus

79. Prussak’s space dysventilation and
attic cholesteatoma
□ COM – thick mucus secretion – closure of
post. Pouch of Von Troeltsch
- selective dysventilation of Prussak’s space
–pars flaccida retraction pocket with adhesion
to malleus neck
- Initially sac of the retraction pocket remains
small and superficial to ossicles
- Continued retraction and keratin accumulation
– enlargement of sac and expansion via
pathways of least resistance

81. PROTYMPANUM
Lies ant. to a frontal line drawn through the ant.
Margin of tympanic annulus
Anteriorly – Eustachian tube
Posteriorly – Mesotympanum
Laterally – Lateral lamina ( separates PT from
mandibular fossa)
Medially – cochlea posteriorly and carotid canal
anteriorly
Roof – bony semicanal for Tensor tympani muscle and
TTF
SUPRATUBAL RECESS
- Superior extension of protympanum
- Lies between superior border of tympanic
orifice of ET and TTF

82. Hypotympanum
Lies below a horizontal plane from inf. margin of fibrous
annulus to inferior margin of cochlear promontory
Five walls
❖ Anterior wall – carotid canal medially and
dense bone laterally
❖ Posterior wall – inferior part of styloid complex
and vertical segment of facial nerve canal
(may contain retrofacial cells)
❖ Outer wall – tympanic bone
❖ Medial wall – lower part of promontory and
petrous bone
❖ Inferior wall – thin bony plate separating from
jugular bulb

83. RETROTYMPANUM
Posterior part of tympanic cavity medial &
posterior to the tympanic annulus
❖ Vertical segment of Facial Nerve & the PE
divides it-
1. The Lateral Space( Facial Recess)
Medially – facial canal and pyramidal eminence
Laterally – chorda tympani
Superiorly – Incudal buttress
Inferiorly – chordo-facial angle (180 - 300)
Chordal ridge – divides facial recess into
-Facial sinus (superiorly)
-Lateral tympanic sinus (inferiorly)

85. 2. The Medial Space
❖ Also called as the Tympanic sinus
❖ Ponticulus divides tympanic sinus to
a. Posterior Tympanic Sinus(Superiorly)
b. Sinus tympani( Inferiorly)- Largest sinus of
Retrotymp.
• In 10% population the sinus tympani and
posterior tympanic sinus form one confluent
recess
• Based on depth sinus tympani is of 3 type
i) Type A(Shallow)
ii) Type B(intermediate)
iii) Type C(very deep)

86. Mesotympanum
Narrowest & biggest compartment
Boundaries
✔ Medially – promontory
✔ Laterally – pars tensa
✔ Anteriorly – protympanum
✔ Posteriorly – retrotympanum
✔ Inferiorly – hypotympanum
✔ Superiorly – Tympanic diaphragm
Acts like a channel allowing air coming from ET
to pass through the Tympanic Isthmus upward
to provide aeration of whole attic

87. TYMPANIC MEMBRANE POUCHES
1. Anterior pouch of Von Troeltsch
- Situated between Anterior Malleal fold and
pars tensa
- Communicates with supratubal recess and
protympanum
2. Posterior pouch of Von Troeltsch
- Situated between posterior Malleal fold and
pars tensa
- Develops posteroinferiorly and opens in the
most cranial portion of mesotympanum
- Main route of ventilation of Prussak’s space

89. MASTOID AIR CELLS
• Vary considerably in number,
form & size
• Interconnected & lined by
squamous non-ciliated
epithelium
• Mastoid processes can be
pneumatic, sclerosed or mixed
• Mastoid process develops by
the age of 2 yrs
• Antrum is well developed at
birth
• Aditus ad antrum is the
opening in the posterior wall of
middle ear and leads
posteriorly to antrum

90. MASTOID ANTRUM
• The roof of mastoid antrum
(tegmin antri) separate it from
middle cranial fossa.
• The lateral:
– Formed by squamous temporal
bone
• Medial wall:
– Related with the posterior and
horizontal semicircular canal
• Posteriorly:
– communicate by several openings with
mastoid air cells.
– Important surgical marks to mastoid
antrum is the MacEwen’s Triangle

91. MACEWEN’S TRIANGLE
• Superior: temporal line
• Anterior: postero-superior
margin of bony external
auditory canal opening
• Posterior: tangent drawn to
mid-point of posterior wall of
external auditory canal
• Contains spine of Henle
• Mastoid antrum lies 12-15
mm deep to triangle

92. KORNER’S SEPTUM
• Membranous persistence of petrous squamous
suture line in temporal bone gives illusion of mastoid
antrum rather true antrum is below this septum
• Residual disease may be left below this septum,if not
realised.

93. BLOOD SUPPLY
• Arteries :
• 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
c) 2)Four 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
• Veins :
• Pterygoid venous plexus
Superior petrosal sinus

94. LYMPHATIC DRAINAGE
• Middle ear :
• Retropharyngeal & parotid nodes
• ET :
• Retropharyngeal group of nodes

95. EUSTACHIAN TUBE
• 36 mm long in adults
• Directed anteriorly, inferiorly & medially from
anterior wall of M.E., forming angle of 450 with
horizontal & sagittal planes
• Enters naso-pharynx 1.25 cm behind
posterior end of inferior turbinate

96. •Lateral 1/3 is bony
Medial 2/3 is fibro-
cartilaginous.
•Junction b/w 2 parts is
isthmus, narrowest part
of Eustachian Tube.

97. •Anatomy of
cartilaginous part:
Cartilage plate lies
postero-medially &
consists of medial +
lateral laminae
separated by elastin
hinge.
•Fibrous tissue +
Ostmann’s fat pad lie
antero-laterally.

98. CHARACTERISTIC ADULT INFANT
Length 36 mm 18mm
Angle with horizontal 45° 10°
Lumen Narrow Wide
Angulation at Isthmus Present Absent
Cartilage Rigid Flaccid
Elastic recoil Effective Ineffective
Ostmann’s fat More Less
Page 119

99. •Blood supply of ET:
• Ascending pharyngeal artery
• Middle meningeal artery
• Artery of pterygoid canal
• Veins drain into pterygoid venous plexus

100. THANK YOU