Anatomy of middle ear

1. Presenter -Dr.Razal M Sherif
Moderator -Dr.Jyothi Swarup R

2. THE MIDDLE EAR CLEFT
• Eustachian Tube
anteriorly
• Middle ear
Cavity/Tympanic Cavity
• Aditus
• Mastoid Antrum
• Mastoid Air Cells
posteriorly

3. Middle Ear Cavity
• The tympanic cavity
o irregular, air-filled space within the temporal bone
o between the tympanic membrane laterally and the
osseous labyrinth of inner ear medially.
• Six sided Cavity
o Roof
o Floor
o Anterior Wall
o Posterior Wall
o Medial Wall
o Lateral Wall
• Contains auditory ossicles ,Intratympanic Muscles

5. ROOF
 Is a thin bony plate
 separates the middle ear from the middle cranial fossa
 called as Tegmen tympani
 formed by both the petrous and squamous portions of the
temporal bone .
 Petrosquamous suture line,
 does not close until adult life,
 can provide a route of access for infection into the middle
cranial fossa from middle ear in children.

6. FLOOR
• Thin bone separates the cavity from the dome of
the Jugular bulb.
• In some cases the floor may be deficient and the
jugular bulb is then covered only by fibrous tissue
and a mucous membrane.

7. LATERAL WALL
• Main part is formed By the Tympanic membrane.
• Superiorly an area of Bone called SCUTUM (outer
attic wall.)

8. ANTERIOR WALL
• The lower-third of the anterior wall
o consists of a thin plate of bone covering the internal
carotid artery
• The middle-third comprises
o the tympanic orifice of the Eustachian tube, which is oval
and 5 x 2mm in size.

9. MEDIAL WALL
separates the Middle ear from the Inner ear.
• Promontory-
o bulging part of on the medial wall which overlies the basal
turn of the cochlea
o has small grooves on its surface containing the nerves
which form the tympanic plexus.
• Tympanic plexus

10. • Oval Window
o Behind and above the promontory is the oval window
o that connects the tympanic cavity with the vestibule,
closed by the footplate of the stapes
o it is 3.25 mm long and 1.75 mm wide.
• Round window
o RW membrane is usually out of sight, obscured by the
overhanging edge of the promontory

11. Ponticulus & Subiculum
• Two small bony projections
are present on the medial
wall, posterior to promontory.
• Ponticulus
o Is the upper projection
posterosuperior to
promontory.
o Above the ponticulus is the
Oval Window
• Subiculum
o Lower projection
posteroinferior to promontory
o Below the subiculum is the
round window

12. • Facial Nerve canal (or Fallopian canal)
o runs above the promontory and oval window in an
anteroposterior direction.
• Processus cochelariformis
o a curved projection of bone on which the tendon of the
tensor tympani muscle takes a hook and turns laterally to
get attached to neck of malleus.
o This forms the landmark for 1st genu of facial nerve –
Posterosuperior to processus cochelariformis

13. POSTERIOR WALL
• The posterior wall is wider above than below.
• Aditus - A large irregular opening in its upper part
• Fossa incudis – A small depression below the aditus,
it houses the short process of the incus and its
suspensory ligament.
• Pyramid - a small hollow conical projection with its
apex pointing anteriorly.
o This houses the stapedius muscle and tendon, which inserts
into the posterior aspect of the neck of stapes.
o Nerve to stapedius runs through the hollow canal with in
the pyramid.

14. Facial Recess & Sinus
tymapni
Facial recess - A 3D space situated between the
• tympanic annulus and chorda tymapni laterally
• Pyramid and vertical portion of facial nerve
medially
Sinus tympani – A 3D space situated between
• Pyramid and vertical portion of facial nerve laterally
• Ponticulus medially
• Also extends deep to promontory
• the most inaccessible site in the middle ear
• Cholesteatoma which has extended to the sinus tympani is
extremely difficult to eradicate

16. Division Of Middle Ear Cavity
• EPITYMPANUM/ATTI
C
• MESOTYPANUM
• HYPOTYMPANUM

17. EPITYMPANUM/ATTIC
• Middle ear cavity above the level of anterior and
posterior Malleolar folds
• Contains
o Head of Malleus, Body of incus, ossicular ligaments and
Mucosal folds.
Prussack Space
• Space between Pars flacida laterally and Neck of
Malleus medially.
• It is the primary site of acquired Cholesteatoma

18. MESOTYPANUM
• Part lying Medial to pars Tensa
o and its air filled space
o Conatins
• handle of MALEUS
• long process of Incus,
• Stapes

19. HYPOTYMPANUM
• Part lying below the lower margin of Tympanic
membrane
• Contains
o Bulge produced by the jugular Bulb
• If the floor is deficient thus jugular bulb may project
into tympanic cavity.

20. Contents Of Middle Ear
• Ossicles
o Malleus
o Incus
o Stapes
• Muscles of Tympanic Cavity
o Tensor Tympani
o Stapedius Muscle

21. 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.
• An anterior ligament arises from the anterior process
to insert into the petrotympanic fissure.

22. Head
Neck
Anterior
Process
Handle
Lateral
Process

23. 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.

24. • 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

25. Body
Short
Process
Facet
Lenticular
Process
Long
Process

26. 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.

27. Anterior Crus
Foot Plate
Head
Neck
Posterior Crus

28. Tympanic Plexus
• It lies over the promontory
o Tympanic Branch of Glossopharygeal Nerve (Jacobsons
Nerve)
o Sympathetic fibers from plexus round internal carotid
artery.
• It supplies
o Tympanic membrane(mucosal Surface)
o Tympanic Cavity
o Mastoid air cells
o Bony estuation tube.
o Carries secrtomotor fibers for parotid gland.

30. Chorda Tympani Nerve
• Branch of Facial Nerve
• Arises from the vertical segment of facial nerve below
the pyramid
• Crosses the posterior tympanic annulus
• Runs over the posteror malleloar fold and in between
the handle of the malleus and long process ,above the
attachment of the tensor tympani
• Leaves the middle ear through the canal of HUGAIER in
the anterior wall
• It carries the taste sensation from ant 2/3 of tongue and
secretomotor fibers to sub maxillary and sub lingual
salivary glands.

31. Muscles In the Tympanic
Cavity
• Tensor Tympani
o Origin –
• cartilaginous part of Eustachian tube
• Bony canal over ET
• greater wing of sphenoid.
o Lies above the Eustachian tube
• enters the middle ear via the canal for tensor tympani in the anterior
wall above the Eustachian tube opening.
o Hooks around the processes cochelariformis on the posterior wall and
then changes the direction laterally and get inserted into neck of malleus.
o Action
• It tenses the tympanic membrane, by pulling the malleus medially
and protects from barotrauma.

33. • Stapedius Muscle
o Orgin - From the Pyramid in the posterior
wall
o Insertion - Neck Of Stapes
o Supplied by Facial Nerve (Nerve to
Stapideus)
o Action - Pulls the Stapes Laterally
(Prevents Barotrauma)

35. Mastoid Process And Air Cells
• Mastoid Process
o Part of temporal bone and situated behind the ear.
o Development by 1 year.
o Based on the degree of pneumatisations
• Celluar – 80% - Fully pneumatised
• Sclerotic – Cells are replaced by dense bones.
• Diploeic – Cells are less and small.

36. o Mastoid antrum
• Biggest and most consistent air cell
• Connected anteriorly to tympanic cavity via the aditus
and posteriorly to other air cells.
• Relations
o Roof – Tegment antri – seperates from middle
cranial fossa.
o Floor – Mastoid portion of temporal bone
o Medial wall – Petrous portion of temporal bone
o Lateral wall –Squamous portion of temporal bone

38. • Mac Ewans triangle
o Landmark for mastoid antrum
o Suprameatal crest above
o Tangential to posterior meatal wall cutting the supra
meatal crest
o Posterior margin of EAC
• Antrum lies postero superior spine of henle.

39. EUSTACHIAN TUBE
• Connects middle ear cavity to nasopharynx.
• From the anterior wall of middle ear it passes
downwards, forwards and medially.
• Length 36mm
o Lateral 1/3rd Bony
o Medial 2/3rd is cartilaginous.
• The pharyngeal end situates 1cm behind and a little
below the end of inferior turbinate.

40. • Functions of ET
o In resting stage collapsed.
On chewing and yawning it opens up.
Helps to equalize air pressure between middle ear and
nasopharynx.
o Controls ventilation of middle ear cleft.
o Helps drainage from middle ear.
• Muscles attached to ET
o Tensor tympani
o Tensor palati
o Levator palati
o Salpingopharynx.