The document describes the anatomy and development of the middle ear walls. It discusses the medial wall, which contains the pyramid, promontory, and oval and round windows. The lateral wall includes the bony outer attic wall and membranous tympanic membrane. The posterior wall forms the mastoid antrum. The anterior wall borders the carotid canal. The tegmen forms the bony roof, while the thin jugular wall separates the middle ear from the internal carotid and jugular bulb below. Understanding the complex anatomy of the middle ear walls is important for ear surgery and diagnosing conditions like cholesteatoma.

1. ANATOMY & DEVELOPMENT
OF THE MIDDLE EAR
SAYAN BANERJEE

11. MEDIAL WALL/
LABYRINTHINE
WALL

12. MEDIAL WALL
• Projection of bone from cochlea
• Tensor tympani muscle takes a turn, moves
laterally and attaches to the handle of
malleus
• Tensor tympani reduces loud excessive
noises like during chewing
• Tensor tympani, tensor veli palatini and
mastication muscles- all are supplied by the
mandibular branch of the trigeminal nerve
• Acts as a landmark for 1st genu of facial
nerve
Connects to scala tympani
M/C site of labyrinthine fistula-
dome of LSCC

14. PROCESSUS COCHLEARIFORMIS
PYRAMID
PROMONTORY
ROUND WINDOW

15. The prominence of the facial
nerve canal indicates the
position of the upper part of the
bony facial canal (Fallopian
canal), which contains the facial
nerve.
The canal crosses the medial
tympanic wall from the
cochleariform process anteriorly,
runs just above the fenestra
vestibuli (oval window), and then
curves down into the posterior
wall of the cavity.
Its lateral wall may be partly
deficient.
Length- 27mm

17. THE PONTICULUS
• It is a bony ridge extending from
the pyramidal process to the
promontory.
• The ponticulus is a central
structure in the retrotympanum.
THE SUBICULUM
• The subiculum is a smooth bony
projection that is situated
posterior to the promontory and
extends inferiorly from the
posterior lip of the round window
niche toward the styloid
eminence.
• Therefore, it intervenes between
the sinus tympani superiorly and
the RW niche inferiorly.

18. • Below and behind the promontory, is the ROUND WINDOW
NICHE, which is directed downward and posteriorly.
Because of such direction of the round window niche the
round window cannot be easily seen from external or lateral
side even through a large perforation of tympanic
membrane.
• The round window is covered by SECONDARY TYMPANIC
MEMBRANE (ROUND WINDOW MEMBRANE), which is
usually out of sight, obscured by the overhanging edge of
the promontory forming the niche and mucosal folds within
it. The membrane is roughly oval in shape, about 2.3 x 1.9
mm in dimension and lies in a plane at right angles to the
plane of the stapes footplate.
• It tends to curve towards the scala tympani of the basal coil
of the cochlea, so that it is concave when viewed from the
middle ear.
• It appears to be divided into an anterior and posterior
portion by a transverse thickening.
• The round window niche is of an average of 2 mm from the
inferior margin of the oval window and is separated from
the promontory by the subiculum.
• The mean width of the RW niche is around 2 mm. Its height
varies up to 1 mm.

20. • Above and behind the promontory is OVAL
WINDOW.
• The Oval window is a kidney-shaped opening that
connects the tympanic cavity with the vestibule,
which is closed by the footplate of the stapes and
its surrounding annular ligament.
• The size of oval window varies with the size of
the footplate, but on average it is 3.25 mm long
and 1.75 mm wide.
• The oval window niche is limited anteriorly and
superiorly by the cochleariform process and
posteriorly by the ponticulus and pyramidal
eminence. It is situated in a depression called the
FOSSULA VESTIBULI where its depth depends on
the position of the facial nerve superiorly, and the
prominence of the promontory inferiorly.
• The bony semicircular cannel lie above and
posterosuperior to oval window, on the medal
aspect of aditus ad antrum.

23. CT SCAN SHOWING MEDIAL WALL OF THE MIDDLE EAR

24. REVISION OF MEDIAL WALL

25. LATERAL WALL/
MEMBRANOUS
WALL

26. BONY LATERAL WALL OF ATTIC/
EPITYMPANIC RECESS
The lateral epitympanic wall is wedge-
shaped in section and its sharp inferior
portion is also called the outer attic wall or
SCUTUM (Latin: ‘shield’). It is thin and
easily eroded by cholesteatoma, leaving a
telltale sign on a high-resolution coronal
CT scan.
MEMBRANOUS LATERAL WALL aka TYMPANIC MEMBRANE
BONY LATERAL WALL OF
HYPOTYMPANUM

27. This explains the difficulty of a
good exposure of the tympanic
membrane in newborns during
otoscopic examination or
paracentesis.
EMBRYOLOGY OF
LATERAL WALL

28. THE PETROTYMPANIC GLASERIAN FISSURE opens anteriorly
just above the attachment of the tympanic membrane. It is a slit
about 2 mm long, which receives the anterior malleal ligament
and transmits the anterior tympanic artery, a branch of the
internal maxillary artery to the tympanic cavity .
THE CANAL OF HUGUIER/ ITER CHORDAE
ANTERIUS is a separate canaliculus placed in the
medial end of the petrotympanic fissure; through this
canal of Huguier, the chorda tympani nerve leaves the
tympanic cavity toward the infratemporal fossa.
ITER CHORDAE POSTERIUS Situated medial to the
posterior tympanic spine. It leads into a minute canal
through which the chorda tympani nerve exits to enter
the tympanic cavity. It lies immediately medial to the
tympanic membrane at the level of the upper limit of
the malleus handle.
The changes in the depth of
the tympanic sulcus reflect
the stability of the annulus
insertion; in the
posterosuperior quadrant, the
annulus is not totally inserted
into the sulcus and is merely
supported. This weak
insertion of the
posterosuperior quadrant of
the tympanic membrane in the
tympanic ring makes it lax and
predisposed to retraction and
skin canal migration.

31. TYMPANIC MEMBRANE---- REVISION

32. CT SCAN SHOWING LATERAL WALL OF THE MIDDLE EAR

33. POSTERIOR
WALL/ MASTOID
WALL

36. ANTERIOR
WALL/ CAROTID
WALL

39. CT SCAN SHOWING ANTERIOR & POSTERIOR WALL OF
THE MIDDLE EAR

40. ROOF/
TEGMENTAL
WALL

41. The TEGMEN is a thin bony plate
that forms the roof of the middle
ear cavity and separates it from the
overlying temporal lobe.
The part of the
Tegmen overlying
the Eustachian
tube is called
TEGMEN TUBARI
The part of the
Tegmen overlying
the mastoid antrum
is called TEGMEN
ANTRI
The part of the
Tegmen overlying
the tympanic cavity
is called TEGMEN
TYMPANI
The superior surface of the tegmen forms part of the
middle cranial fossa floor and is covered by the dura;
the inferior surface of the tegmen is lined by middle
ear mucosa. The tegmen separates the CSF superiorly
from the air space of the middle ear inferiorly.

42. FLOOR/ JUGULAR
WALL

43. The floor of the middle ear cavity
is narrow and consists of a thin
plate of bone that separates the
middle ear from the jugular bulb
posteriorly and the internal carotid
artery anteriorly.
In the bone between the carotid artery
canal and the jugular bulb fossa, near the
medial wall, opens a small canal, THE
INFERIOR TYMPANIC CANALICULUS,
localized near the fossula petrosa which
houses the inferior ganglion of the
glossopharyngeal nerve (CN IX). It is
often a faintly marked depression on the
inferior surface of the petrous portion of
the temporal bone.
The floor of the middle ear cavity is narrow and consists of a thin plate of bone that separates
the middle ear from the jugular bulb posteriorly and the internal carotid artery anteriorly. THE
INFERIOR TYMPANIC CANALICULUS (*) in the inferior wall gives passage for the Jacobson’s
nerve originating from the inferior ganglion of IX which is located in the jugular fossa bulb
and the inferior tympanic artery (branch of the ascending pharyngeal artery).
 The surface of this
wall may show
irregularities due
to the overlying
pneumatized cells.
 In the posterior
part of the floor is
the root of the
styloid process
which gives rise to
a bony eminence,
the STYLOID
EMINENCE.

44. CT SCAN SHOWING ROOF & FLOOR OF THE MIDDLE EAR

45. SUMMARY OF MIDDLE EAR WALLS