4. Middle ear together with the eustachian
tube ,aditus ,antrum and mastoid air cells is
called as MIDDLE EAR CLEFT.
The middle ear extends beyond the limits of
tympanic membrane which forms its lateral
boundary and sometimes divided into
Epitympanum(above pars tensa)
mesotympanum (opp:pars tensa)
hypotympanum(below pars tensa)
Middle ear can be linked to a six sided box with a
roof ,a floor ,medial ,lateral ,anterior and posterior
walls.
5.
6. Thin plate of bone called TEGMEN TYMPANI .
It also extends posteriorly to form the roof of the
aditus and antrum.
It seperates tympanic cavity from the middle
cranial fossa.
7. Thin plate of bone which seperates tympanic
cavity from the jugular bulb.sometimes,it is
congenitally deficient and the jugular bulb may
then project into middle ear ;seperated from the
cavity only by the mucosa.
9. Thin plate of bone which seperates the cavity from
the internal carotid artery.it also has two openings
; the lower one for the eustachian tube and the
upper one for the canal of tensor tympani muscle.
10. It lies close to the mastoid aircells.It presents a bony
projection called the pyramid through the summit of
which appears the tendon of the stapedius muscle to
get attachment to the neck of stapes .
Aditus, an opening through which attic communicates
with the antrum.
Facial nerve runs in the posterior wall just behind the
pyramid.
Facial recess is a depression in the posterior wall
lateral to the pyramid.
It is bounded medially by the vertical part of7th nerve
laterally by the chorda tympani and above by the fossa
incudis.
11.
12. It is formed by labyrinth.
It has
1)a bulge called promontory
2)oval window into which foot plate of stapes is
fixed.
3)round window which is covered by secondary
tympanic membrane.
4)just anterior to the oval window, the medial wall
presents a hook like projection called the
processus cochleari formis, which marks the level
of the genu of facial nerve.
14. It is formed largely by the tympanic membrane .
The tympanic membrane is semi transparent and
forms a window into the middle ear.
15. ADITUS: is an opening through which the attic
communicates with the antrum.
Facial nerve courses just below the aditus.
MASTOID ANTRUM: is a large air containing space in
the upper part of mastoid and communicates with the
attic through the aditus.
The mastoid consists of bone cortex with a “honeycomb”
of aircells underneath.
Its roof is formed by the tegmen antri which is a
continuation of the tegmen tympani and seperates it from
the middle cranial fossa.
The lateral wall of the antrum is formed by a plate of
bone.
Its is marked externally on the surface of mastoid by
supra meatal(MACEWEN‟S ) triangle.
16.
17.
18.
19.
20. There are three ossicles in the middle ear
malleus,incus and stapes.
21.
22. MALLEUS: has head ,neck ,handle (manubrium),
lateral and anterior process.
INCUS: has body , short process , long process and
a lenticular process .
STAPES: has a head,neck, anterior and posterior
crura and a foot plate.
The ossicles conduct sound energy from the
tympanic membrane to the oval window and then
to the inner ear fluid.
23. 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
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
24. TYMPANIC PLEXUS:
1)tympanic branch of glossopharyngeal
2)sympathetic fibres from plexus round the ICA.
CHORDA TYMPANI NERVE: branch of facial
nerve, passes through the middle ear.
27. o Pathology can be well estimated on otoscopic
examination,further questions like extent of
disease,exact location,structures involved and
possible bone erosions ,will be addressed in detail
only with CT&/MRI.
o The majority of everyday practise cases will
consists of inflammatory disease ,either
chronic/acute&sometime tumours.
o On CT examination,these entities will
demonstrate a MASS /DIFFUSE
OPACIFICATION OF MIDDLE EAR CAVITY.
28.
29.
30. Images should be viewed in correct bone window
setting –large window width(4000HU)&low
window level(0-200HU)
In order to evaluate possible ossicular erosion,
axial CT images should be searched for „3‟
distinctive signs:
1.Icecream cone .
2.Two parallel lines.
3.Two dots.
31. Axial CT bone window:long arrow –malleus head
and short arrow- incus body.(1.ICE CREAM CONE
APPEARANCE)
