Anatomy of Middle ear with clinical correlation

1. ANATOMY OF MIDDLE EAR
- Dr.Saneesh Damodaran
JR-1, OTORHINOLARYNGOLOGY

2. MIDDLE EAR [ TYMPANIC CAVITY ]
• Communications:
• Anteriorly to Nasopharynx via
Auditory tube (Eustachian Tube).
• Posteriorly to Mastoid Antrum via
Adittus.
MIDDLE EAR
CLEFT

3. EMBRYOLOGY OF MIDDLE EAR
• Eustachian tube, Tympanic cavity,
Attic, Mastoid air cells – develop
from Endoderm of TuboTympanic
recess (which arise from 1st
Pharyngeal pouch)
• Maleus and Incus develop from
Mesoderm of 1st Arch; while
Stapes develop from 2nd Arch
(except its Footplate and Annular
Ligament – derived from Ottic

4. TYMPANIC
CAVITY
PART
S
WALL
S

5. ROOF TYMPANIC CAVITY FLOOR
• Thin plate of bone – Tegmen
Tympani – seperates from Middle
Cranial Fossa.
• Extends Posteriorly to form roof of
Adittus and Antrum – Tegmen
Antrii.
• Thin plate of bone – separates from
Jugular Bulb.
• Medial border – small aperture for
Tympanic branch of CN IX enter
Middle ear.

6. TYMPANIC CAVITY – ANTERIOR WALL
• Upper part – Canal of Tensor
Tympani and Eustachian Tube
opening.
• Lower part - Thin plate separates
cavity from Internal Carotid Artery.

7. TYMPANIC CAVITY - LATERAL WALL
• Membranous – Tympanic
Membrane
• Bony –
Lateral Attic Wall above Pars
Flaccida Lateral Wall of
HypoTympanum.

8. TYMPANIC
CAVITY
– MEDIAL WALL
• Promontory
• Oval Window
• Round Window
• Tympanic part of
bony-
Facial Nerve
Canal
• Lateral Semi-Circular
Canal
• Processus

9. PROMONTORY
• Rounded elevation covering
most of Medial wall.
• Formed by Basal turn of
Cochlea.
• Small groves on surface –
Nerves that form Tympanic
Plexus.

10. OVAL WINDOW
• Behind Promontory.
• Kidney shaped opening -
connects with Vestibule.
• Covered by Footplate of Stapes.
• 3.25 x 1.75mm

11. ROUND WINDOW
• Behind Oval Window - Seperated by
Subiculum (Post. Extension of
Promontory)
• Ponticulus (another Ridge above
Subiculum) – runs to Pyramid on Post
Wall.
• Sinus Tympani – where Ponticulus
and Subiculum meet.
• 2.3 x 1.9mm
• Right angle to Stapes Foot plate.

12. FACIAL NERVE CANAL [FALLOPIAN CANAL]
• Runs above Promontory and Oval window in
Antero-Medial direction.
• Marked Anteriorly by Processus Cochleaformis
(bone with concave anteriorly houses Tendon of
Tensor Tympani)
• In Medial wall – level above Facial Canal is
Epitympanum.
• Dome of Lateral SCC – lies in Post portion of
Epitympanum, extending little Lateral to Facial
Canal.
• Behind Oval Window, Facial Canal starts to turn

14. TYMPANIC CAVITY - POSTERIOR WALL
• Adittus ad Antrum
• Fossa Incudis for Short Process of
Incus.
• Bulge d/t Lateral SCC.
• Pyramidal eminence for Stapedial
tendon.
• Bulge d/t Vertical part of Facial
Nerve.
• Sinus Tympani

15. TYMPANIC CAVITY - POSTERIOR WALL
(COND….)
• Post wall is Wider above.
• Aditus ad Antrum – Upper part,
that leads to Mastoid Antrum.
• Fossa Incudis – Small depression
below Aditus – houses Short
Process of Incus and its
Suspensory ligament.
• Pyramid – below Fossa Incudis and
medial to opening of Chorda
Tympani.

16. FACIAL RECESS
• Groove b/w Pyramid and Annulus
of TM.
• Boundaries:
• Medial: Facial N.
• Lateral: Tympanic Annulus.

17. SINUS TYMPANI
• Boundaries:
• Superior: Ponticulus
• Inferior: Subiculum
• Lateral: Mastoid seg of Facial
N
• Medial: Post SCC
• Site for Cholesteatoma
reccurence – as it’s not directly
visualized during surgery.

18. OSSICLES

19. MUSCLES OF MIDDLE EAR
MUSCLE ORIGIN INSERTION NERVE SUPPLY ACTION
Tensor
Tympani
Cartilaginous
part of ET, its
own Bony Canal
Upper part of
Handle of
Malleus
Branch from
Mandibular N
[V3]
Tensing Tympanic
Membrane to reduce the
force of vibrations in
response to loud noises
Stapedius Pyramidal
Eminence
Neck of Stapes Branch of Facial
N
Pulls the Stapes
posteriorly and prevents
excessive oscillation in
loud noises

20. CHORDA TYMPANI NERVE
• Chorda Tympani enters Tympanic cavity
from Post Canaliculus at jn of Lat and
Post Walls - runs Obliquely – across
Medial surface of TM (b/w Mucosal and
Fibrous layers) – then pass Medially to
upper portion of Handle of Malleus
(above tendon of Tensor Tympani) –
leaves through PetroTympanic Fissure.
• Angle b/w Facial N and Chorda – in
Posterior Tympanotomy (access Middle

21. TYMPANIC PLEXUS
• Formed over Promontory by:
• Tympanic branch of CN IX
(Jacobson’s N)
• CaroticoTympanic N’s
(arise from Sympathetic plexus around Int
Carotid A)
• Supply Mucous membrane lining Tympanic
Cavity, Eustachian Tube, Mastoid Antrum and
Air cells.
• The Plexus also provides branches to join
Greater Sup. Petrosal N and Lesser Sup.

22. MASTOID AIR CELLS
• Vary in number, form and size.
• Interconnected & lined by
Squamous Non-ciliated epithelium.
• Mastoid Process – Develop by age
2yrs.
• Pneumatic / Sclerosed / Diploic.
• Antrum – well developed at Birth.

23. MASTOID ANTRUM
• Relations:
• Lateral: Squamous Temporal
bone.
• Medial: Post and Horizondal
SCC.
• Posterior: Communicates with
Mastoid Air Cells via. Several
openings.

24. MAC EWEN’S TRIANGLE
• Superior: Temporal line.
• Anterior: Postero-Superior margin of
bony EAC opening.
• Posterior: Tangent drawn to Mid-point
of Post. Wall of EAC.
• Contains Spine of Henle.
• Mastoid Antrum lies 12-15mm deep to
Triangle.

25. MUCOSA OF MIDDLE EAR CLEFT
• Mucus membrane of Nasopharynx is
continuous with Middle Ear, Aditus and Antrum.
• Secretes Mucus
• Respiratory type – has Cilia.
• Lines Bony wall of Tympanic cavityand wraps
Middle ear structures (Ossicles, Muscles,
Ligaments and Nerves) like Peritonium wraps
viscera of abdomen.

26. FACIAL NERVE
• Meatal seg: 8-10mm
• Labyrinthine seg: 4mm
• Tympanic seg: 11mm
• Mastoid seg: 13mm
• 3 branches in Intra-
Temporal part
• Greater Petrosal N
• Nerve to Stapedius
• Chorda Tympani

27. BLOOD SUPPLY – MIDDLE EAR
• 2 Main Arteries:
• Ant. Tympanic branch of Maxillary A.
• StyloMastoid branch of Post Auricular
A.
• 4 Minor Arteries
• Petrosal branch of Middle Meningeal
A.
• Sup. Tympanic branch of Middle
Meningeal A.
• Branch of Artery of Pterygoid Canal.
• Veins:
• Pterygoid venous plexus.
• Superficial Petrosal Sinus.
• Lymphatic Drainage -
• Middle Ear: RetroPharyngeal &
Parotid nodes.
• ET: RetroPharyngeal group of
nodes.

28. EUSTACHIAN TUBE
• Direction – Anterior, Inferior,
Medially from Ant. Wall of Middle Ear
(45° with Horizondal and Sagittal
planes)
• Enters Nasopharynx 1.25cm behind
Post. End of Inf. Turbinate.
• Lateral 1/3 – Bony;
• Medial 2/3 – FibroCartilagenous.
• Junction b/w 2 parts – Isthmus.

29. EUSTACHIAN TUBE

30. EUSTACHIAN TUBE
• Cartilaginous part
• Postero-Medial: Cartilage Plate. Medial
and Lateral Laminae separated by
Elastin Hinge.
• Antero-Lateral: Fibrous Tissue and
Ostmann’s Fat pad.
• Ascending Pharyngeal Artery
• Middle Meningeal Artery
• Artery of Pterygoid Canal
• Veins drain into Pterygoid Venous

31. EUSTACHIAN TUBE – BLOOD SUPPLY
• Ascending Pharyngeal Artery
• Middle Meningeal Artery
• Artery of Pterygoid Canal
• Veins drain into Pterygoid Venous Plexus

32. THANK
YOU