Anatomy and ultrastructure of middle ear

Dr. Raju Kafle
1st Year Resident
Dept. ENT-HNS
ANATOMY AND
ULTRASTRUCTURE OF MIDDLE
EAR

Tympanic cavity and Auditory tube
 The tympanic cavity, which originates
in the endoderm, is derived from the
first pharyngeal arch.
 This pouch expands in a lateral
direction and comes in contact with
the floor of the first pharyngeal cleft.
 The distal part of the pouch, the
tubotympanic recess, widens and gives
rise to the primitive tympanic cavity
 The proximal part remains narrow
and forms the auditory tube through
which the tympanic cavity
communicates with the nasopharynx3

Ossicles and mastoidThe malleus and incus are derived from
cartilage of the first pharyngeal arch.
The stapes is derived from that of the
second arch
 Although the ossicles appears during
the first half of fetal life, they remain
embedded in mesenchyme till 8th
month when the surrounding tissue
dissolves .
The endodermal epithelial lining of the
primitive tympanic cavity then extends
along the wall of the newly developing
space.
The tympanic cavity is now at least twice
as large as before.4

5
 When the ossicles are entirely free of surrounding mesenchyme, the
endodermal epithelium connects them in a mesentery-like fashion to the
wall of the cavity .The supporting ligaments of the ossicles develop later
within these mesenteries.

 Since Malleus is derived from the first pharyngeal arch, its
muscle, the tensor tympani, is innervated by the mandibular
branch of the trigeminal nerve.
 The stapedius muscle, which is attached to the stapes, is
innervated by the facial nerve, the nerve to the second
pharyngeal arch.
 During late fetal life, the tympanic cavity expands dorsally by
vacuolization of surrounding tissue to form the tympanic
antrum.
 After birth, epithelium of the tympanic cavity invades bone of
the developing mastoid process, and epithelium-lined air sacs are
formed (pneumatization)
 .
6

7
 Later, most of the mastoid air sacs come in contact with the
antrum and tympanic cavity.
 Expansion of inflammations of the middle ear into the antrum
and mastoid air cells is a common complication of middle ear
infections.

Anomalies:
 Malformed ossicles
 Fused stapes
 Anomalies course of Facial nerve
 Persistent Stapedial artery
 Aberrant internal carotid artery
 High jugular bulbs
8

THE MIDDLE EAR CLEFT
The middle ear cleft consists of the;
1. Tympanic cavity
2. Eustachian tube
3. Mastoid ear cell system
Communications:
Anteriorly : via ET
Posteriorly: via aditus to mastoid air cells
9

Divided into three compartments:
 The epitympanum or attic
 The mesotympanum
 The hypotympanum
11

12
 Epitympanum : above malleolar fold
 Mesotympanum: opposite of TM, visible from EAC with
a microscope
 Hypotympanum: below tympanic sulcus
 Protympanum: anterior to promontory and contiguos with
tympanic portion of ET
 Retrotympanum:posterior to mesotympanum, includes both
posterior and posteromedial walls of tympanic cavity

The LATERAL WALL
 The lateral wall of the tympanic cavity is
formed by;
- Superiorly: Bony lateral wall of the
epitympanum.
- Centrally: Tympanic membrane and,
- Inferiorly: Bony lateral wall of the
hypotympanum.
15

16
 Lateral epitympanic wall : wedge shaped,
sharp inferior portion = scutum ( latin :
shield)or outer attic wall, formed by the
superior wall of the external auditory canal
and the lateral wall of the tympanic cavity.
 It forms the lateral margin of Prussak space.(
between pars flaccida and neck of malleus,
bounded by lateral malleolar fold))
 Thin and eroded by cholesteatoma , leaving a
TELLTALE SIGN on high resolution on CT
Coronal section

 Petrotympanic fissure (Glasserian
fissure), 2mm ,from temporomandibular
joint to tympanic cavity, opens anteriorly
just above the attachment of the tympanic
membrane.
 It contains the anterior malleolar ligament
and transmits the anterior tympanic branch
of the maxillary artery to the tympanic
cavity.
 The chorda tympani nerve enters the
medial surface of the fissure through a
separate anterior canaliculus (canal of
Huguier) which is sometimes confluent with
the fissure.
17

18
 It then runs posteriorly between the fibrous
and mucosal layers of the tympanic
membrane, across the upper part of the handle
of the malleus and then continues within the
membrane, but below the level of the posterior
malleolar fold
 The nerve reaches the posterior bony canal
wall just medial to the tympanic sulcus, enters
the posterior canaliculus.It then runs
obliquely downwards and medially through
the posterior wall of the tympanic cavity until
it reaches the facial nerve

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.
During cortical mastoidectomy, the fibrous strands of the tympanomastoid
suture line can often be confused with the chorda tympani although the angle
of the white strands of the suture line is different from the angle of the chorda.
The nerve carries taste sensation from the anterior two- thirds of the same
side of the tongue and secretomotor fibres to the submandibular gland.
19

21
 The roof of the epitympanum is the tegmen
tympani- 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.

22
 Cog: bony crest , projection from tegmen tympani caudally and
anterior to head of malleus . Variable in size
 Divides epitympanum into larger posterior epitympanic space and
smaller anterior epitympanic space
 Residual cholesteatoma if not formally explored in canal up surgery.

24
 The floor of the tympanic cavity separates the
hypotympanum from the dome of the 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 ( Jacobsons nerve) into the
middle ear.

THE ANTERIORWALL…
The anterior wall of the tympanic cavity is rather
narrow as the medial and lateral walls converge.
Upper-third is usually pneumatized and may house
the anterior epitympanic sinus, a small niche anterior to
the ossicular heads, which can hide residual
cholesteatoma in canal wall up surgery.
Middle-third - tympanic orifice of the Eustachian
tube.
It is oval and 5 x 2 mm in size. Just above this is a
canal containing the tensor tympani muscle that
subsequently runs along the medial wall of the tympanic
cavity enclosed in a thin bony sheath.
26

27
 Lower-third : thin plate of bone covering the
carotid artery.
 This plate is perforated by the superior and inferior
caroticotympanic nerves (which carry sympathetic
fibres to the tympanic plexus) and tympanic branches
of the internal carotid artery.

29
The medial wall separates the tympanic cavity
from the internal ear.
The promontory is a rounded elevation
occupying much of the central portion of the
medial wall.
It covers part of the basal coil of the cochlea and
usually has small grooves on its surface
containing the nerves which form the tympanic
plexus.

30
 Sometimes the groove containing the tympanic branch of the
glossopharyngeal nerve may be covered by bone, thereby forming a
small canal.
 The promontory gently inclines forwards to merge with the anterior
wall of the tympanic cavity, but is more steeply sloped posteriorly.

Oval window( fenestra vestibuli)
Behind and above the promontary
It 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.
Its size 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 can be of varying width
depending on the position of the facial nerve
superiorly, and the prominence of the promontory
inferiorly.
31

Round window niche( fenestra cochleae)
Lies below and a little behind the oval window niche
from which it is separated by a posterior extension of
the promontory called the subiculum
Another ridge of bone, the ponticulus, leaves the
promontory above the subiculum and runs to the
pyramid on the posterior wall of the cavity
The round window niche is most commonly
triangular in shape, with anterior, posterosuperior and
posteroinferior walls
The latter two meet posteriorly and lead to the sinus
tympani.32

The facial nerve canal (Fallopian canal) runs above
the promontory and oval window in an anteroposterior
direction.
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.
33

34
 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 tympanic cavity.

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 pyramid, a small hollow
conical projection with its apex pointing anteriorly.
36

37
 This houses 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.

Facial recess
 Groove between pyramid and facial nerveand annulus of tympanic
membrane
 Medially: Facial nerve
 Laterally: Tympanic annulus
 With the chorda tympani running obliquely through wall between the two.
 The angle between the facial nerve and Chorda allows a Posterior
tympanotomy– allowing access to the middle ear from mastoid without
disrupting the tympanic membrane.
38

 The sinus tympani is a posterior extension of the
mesotympanum and lies deep to both the promontory
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.
41

42
 Cholesteatoma which has extended to the sinus
tympani from the mesotympanum is extremely difficult
to eradicate.
• The worst region for access is above the
pyramid, posterior to an intact stapes and
medial to the facial nerve.
 A retrofacial approach to this region via the mastoid
is not possible because the posterior semicircular
canal blocks the access.

CONTENTS OF THE TYMPANIC CAVITY
The ossicles,
Two muscles,
The chorda tympani
The tympanic plexus.
The malleus is the most lateral and is attached to the tympanic
membrane, whereas the stapes is attached to the oval window.
44

THE MALLEUS ( The hammer )
The malleus is the largest of the three ossicles, measuring up to 9 mm in
length.
It comprises a head, neck and handle or manubrium.
The head lies in the epitympanum and is suspended by the superior
ligament, which runs upward to the tegmen tympani.
The head of the malleus has a saddle-shaped facet on its posteromedial
surface to articulate with the body of the incus by a synovial joint.
Below the neck of the malleus, the bone broadens and gives rise to the
lateral process, the anterior process and the handle.
The lateral process is a prominent landmark on tympanic membrane the
and receives the anterior and posterior malleolar folds from the tympanic
annulus
46

47
 The handle is very closely attached to the membrane at its lower end,
there is a fine web of mucosa separating the membrane from the handle
in the upper portion before it becomes adherent again at the lateral
process.
 This can be opened surgically to create a slit without perforating the
membrane to allow a prosthesis to be crimped around the malleus
handle in certain types of ossicular reconstruction.
 On the deep, medial surface of the handle, near its upper end, is a small
projection into which the tendon of the tensor tympani muscle inserts.

THE INCUS (Theanvil)
The incus articulates with the malleus and has a body and two processes.
The body lies in the epitympanum and has a cartilage- covered facet
corresponding to that on the malleus. The body of the incus is suspended by
the superior incudal ligament that is attached to the tegmen tympani.
The short process projects backwards from the body to lie in the fossa
incudis to which it is attached by a short suspensory ligament.
The long process descends into the mesotympanum behind and medial to
the handle of the malleus, and at its tip is a small medially directed lentiular
process.
It has been called the fourth ossicle because of its incomplete fusion with
the tip of the long process, giving the appearance of a separate bone or at
least a sesamoid bone.
The lenticular process articulates with the head of the stapes.
49

THE STAPES (The stirrup)
50
 The stapes is shaped like a stirrup and consists of a head, neck, the
anterior and posterior crura and a footplate.
 The stapedius tendon inserts into the posterior part of the neck and
upper portion of the posterior crus.
 The two crura arise from the broader lower part of the neck and the
anterior crus is thinner and less curved than the posterior one.
 Both are hollowed out on their concave surfaces, which gives an
optimum combination of strength and lightness.
 The two crura join the footplate, which usually has a convex superior
margin, an almost straight inferior margin and curved anterior and
posterior ends.

THE STAPEDIUS MUSCLE
The stapedius arises from the walls of the conical
cavity within the pyramid.
A slender tendon emerges from the apex of the
pyramid and inserts into the neck of stapes.
The muscle is supplied by a small branch of the facial
nerve.
Action: Pulls stapes posteriorly and prevents
excessive oscillation in loud noise.
51

THE TENSOR TYMPANI MUSCLE
52
 It arises from the walls of the bony canal lying
above the Eustachian tube.
 Parts of it also arise from the cartilaginous
portion of the Eustachian tube and the greater wing
of the sphenoid.
 The bony covering of the canal is often deficient
in its tympanic segment where the muscle is
replaced by a slender tendon

53
 This enters the processus cochleariformis where it is held down by a
transverse tendon as it turns through a right angle to pass laterally and
insert into the medial aspect of the upper end of the handle of malleus .
 Mandibular nerve
 Action: Tenses tympanic membrane to reduce the force of vibrations in
response to loud noise

THECHORDA TYMPANI NERVE
Enters the tympanic cavity from the posterior
canaliculus at the junction of the lateral and posterior
walls.
It run 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.
54

THE TYMPANIC PLEXUS
Formed by
The tympanic branchof 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.
55

Linings of middle ear
56
 ET : pseudostratified ciliated columnar and columnar
 Tympanic cavity:
 Anterior and inferior part : ciliated columnar
 Posterior part: cuboidal
 Epitympanum and mastoid air cells : flat squamous ,
non ciliated

Mucosal folds
57
Mucosal folds extend from the wall of middle ear to its content & carry
ligaments and blood vessels to the ossicles.
These folds orient the progress of middle ear pathologies but are not true
barrier against their extension.
Mucosal folds- two types
 Composite fold: ligament+ lining mucosa ex:Ant.MLF, Lat.MLF and
Post. Incudal fold
 Duplicate fold: fusion of two expanding air sac walls in absence of
any interposing structure. ex: tensor tympani fold, lateral
incudomalleal fold.

Important folds in middle ear:
58
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

THEEUSTACHIAN TUBE
61
Discovered by : Bartolomeus
eustachius, 1562
(pharyngotympanic tube)
Named by antonia Valsalva later.

It is a dynamic channel that links the middle ear with
the nasopharynx.
Length = 36 mm (reached by the age of 7)
It runs downwards from the middle ear at 45° and is
turned forwards and medially.
The lateral third is bony and arises from the anterior
wall of the tympanic cavity
Medial two-thirds cartilaginous part.
62

63
Cartilagenous part = 24mm, fibrocartilageneous skeleton to which peritubal
muscles attached.
At its upper border , cartilage is bent over to resemble an inverted J , forming
longer medial cartilagenous lamina and shorter lateral cartilageneous lamina
The cartilage is fixed to the base of skull in groove between petrous part of
temporal bone and greater wing of sphenoid, terminates near the root in the median
pterygoid plate.
Thus the back( posteromedial ) wall is composed of cartilage and the front (
anterolateral ) walls comprises cartilage and fibrous tissue

Its narrowest portion i.e, isthmus -diameter 0.5 mm or less.
It is lined with respiratory mucosa containing goblet cells and mucous
glands, having ciliated epithelium on its floor.
At its nasopharyngeal end, the mucosa is truly respiratory; but in passing
along the tube towards the middle ear, the number of goblet cells and glands
decreases, and the ciliary carpet becomes less profuse
It runs through the squamous and petrous portions of the temporal bone,
gradually tapering to the isthmus.
A thin plate of bone forms the roof, separating the tube from the tensor
tympani muscle above. The carotid canal lies medially and can impinge on the
bony Eustachian tube.64

65
Ostmann’s pad: Triangular layer of fatty tissues,
lateral side of cartilageous part.
Keeps the tubes closed, prevent reflux of
nasopharyngeal secretions

67
The apex of the cartilage is attached to
isthmus of the bony portion , while the
wider medial end protudes into
nasopharynx, lying directly undrer the
mucosa to form TORUS TUBARIUS
Opens in nasopharynx = 1- 1.25 cm behind
and below the posterior end of inferior
turinate, triangular in shape.
Gerlach tonsil( Tubal tonsils)
Fossa of Rosenmuller

Muscles attached to ET
68
Tensor veli palati ( dilator tubae): arises from bony wall and from whole
length of lateral carilagenous lamina that forms the upper portion of the the
front wall of cartilagenous tube.
Supplied by mandibular nerve
Salpingopharyngeus is attached to the inferior part of the cartilage of the
tube near its pharyngeal opening, and it descends to blend with the
palatopharyngeus.

69
Levator veli palati arises from the lower
surface of the cartilaginous tube and from
the lower surface of the petrous bone, and
from fascia forming the upper part of the
carotid sheath.
It first lies inferior to the tube, then crosses to
the medial side and spreads out into the soft
palate.
Salpingopharyngeus and the levator palati
are supplied from the
pharyngeal plexus.

70
The ascending pharyngeal and middle meningeal arteries
supply the Eustachian tube.
The veins drain into the pharyngeal plexus and the lymphatics pass to
the retropharyngeal nodes.
The nerve supply arises from the pharyngeal branch of the
sphenopalatine ganglion (Vb) for the ostium, the nervus spinosus (Vc)
for the cartilaginous portion and from the tympanic plexus (IX) for the
bony part.

 The mastoid antrum( volume = 2mL) is
an air-filled sinus in the petrous part of
temporal bone.
 It communicates with the middle ear by the
aditus.
 Antrum is well developed at birth and most
constant air cells.
 Boundaries
72

 Mastoid consists of bone cortex and air cells.
 Develops from squamous & petrousbones
 Korner’s septum
 3 types of mastoid with thin intervening septa.
 Diploetic- mastoid with marrow spaces & few
air Cells
 Well-pneumatised or cellular-well developed
cells
 Sclerotic or acellular- no cells/marrow spaces
73

Depending on location, mastoid cells are divided:
 Zygomatic
 Tegmen
 Perisinus
 Retrofacial
 Perilabyrinthine
 Peritubal
 Tip
 Marginal
 Squamosal74

Five Recognized tracts:
 The posterosuperior tract runs at the junction of the posterior and
middle cranial fossa aspects of the temporal bone.
 The posteromedial cell tract parallels and runs inferior to the
posterosuperior tract.
 The subarcuate tract passes through the arch of the superior
semicircular canal.
 The perilabyrinthine tracts run superior and inferior to the bony
labyrinth
75

76
 Peritubal tract surrounds the eustachian tube.
 The anterior petrous apex is pneumatized in only 10 to 15% of
specimens. Most often, it is diploic; in a small percentage of cases, it is
sclerotic.
 Petrous apex: most medial of temporal bone, three important structures,
and petrositis

78
In most of the population, the mastoid air cell system is fairly extensive
with air cells.
Alternatively, the mastoid antrum may be the only airfilled space in the
mastoid process when the name acellular or sclerotic is applied.
Seen only in 20 percent of adult temporal bones and is seen in
individuals with chronic ear disease.
Normally lining of the mastoid is a flattened, nonciliated epithelium
without goblet cells or mucus glands

80
MacEwen's triangle:
• Posterior prolongation of the line of
the zygomatic arch ( temporal line)
•Posterosuperior margin of EAC
• Tangent to this, that passes through
the posterior border of the external
auditory meatus.
•Contains Spine of henle
•Mastoid antrum : 12-15 mm deep to
triangle

Artery supply of middle ear
81
Six arteries :
2 major
 Anterior tympanic branch of maxillary artery : supplies TM
Stylomastoid branch of posterior auricular artery which supplies
middle ear and mastoid air cells
4 minor
Petrosal branch of middle meningeal artery
Superior tympanic branch of middle meningeal artery
Branch of artery of pterygoid canal
Tympanic branch of nernal carotid artery

82
Veins : pterygoid venous plexus and superior petrosal
sinuses.
Lymphatic drainage
 Middle ear : Retropharyngeal and parotid nodes
 Auditory tube : Retropharyngeal node

BRANCH PARENT ARTERY REGION SUPPLIED
1 ANT
TYMPANIC
MAXILLARY TM,MALLEUS,INCUS,ANT
TYMPANIC CAVITY
2 STYLOMASTOID POST AURICULAR POSTPART 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 ARTERYOF PTERYGOID
CANAL
MESOAND HYPOTYMPANUM
8 TYMPANIC
ARCHES
INTERNAL CAROTID MESOAND HYPOTYMPANUM
83

Anatomy and ultrastructure of middle ear

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Anatomy and ultrastructure of middle ear

Similar to Anatomy and ultrastructure of middle ear (20)

More from raju kafle

More from raju kafle (14)

Recently uploaded

Recently uploaded (20)

Anatomy and ultrastructure of middle ear

Editor's Notes