Anatomy of ear and mastoid

Anatomy of ear and mastoid is a must know topic for undergraduate and postgraduate ENT students. In this lecture, Dr Krishna Koirala will be explaining about the anatomy of ear and mastoid in a clear and simplified way.

1. Anatomy of ear
and mastoid
Dr. Krishna
Koirala

2. •Paired sensory organs comprising of
•Auditory system involved in the
detection of sound
•Vestibular system involved in
maintaining body balance and
equilibrium
•Divided anatomically and functionally
into
•External ear
•Middle ear
•Inner ear
•All three regions are involved in hearing
•Inner ear is involved in body balance and
equilibrium

4. External Ear (Outer
Ear)

5. Pinna

Framework formed by yellow elastic
cartilage except in the lobule and
incissura terminalis

Functions

Collect and direct sound waves through
the ear canal to the tympanic
membrane

Protect the tympanic membrane

Importance : Graft material for middle
ear & other reconstructive surgeries

6. 
Helix: Slightly curved rim of the auricle

Antihelix: Broader curved eminence
anterior to helix

Concha : Deep cavity in front of the helix

Cymba conchae : Depression between the
antitragus and ascending crus of the helix
(surface landmark of mastoid antrum)

Tragus

Lobule : Structure made up of areolar
tissue & fat without cartilage

8. Sensory Nerve supply of pinna
Lateral surface
Upper 2/3 : Auriculotemporal nerve
(cranial nerve V)
Lower 1/3 : Greater auricular nerve
(C2,3)
Medial Surface
Upper 1/3: Lesser occipital nerve (C2)
Lower 2/3 : Greater auricular nerve (C2,
3)
Posterior concha and antihelix : Auricular
b/o Vagus
Facial : Small region at the root of
concha

9. External Auditory canal

10. 
Extends from bottom of concha to the
tympanic Membrane

24 mm long in adults

Lateral 1/3 (8 mm) Cartilaginous :
Directed upwards, backward and
medially

Medial 2/3 (16 mm) Bony : Directed
downwards, forward and medially

Pinna to be pulled upwards, backwards
and laterally to straighten the external
auditory canal in adults

11. Only cartilaginous skin has hair
follicles, ceruminous and
pilosebaceous glands (wax)
Cartilaginous fissure of Santorini
and bony foramen of Huschke
present in anterior wall 
infection / metastasis to and from
the parotid gland

12. Middle EarMiddle Ear

13. Middle ear cleft

Middle ear cavity

Attic ,aditus,
antrum

Mastoid air cell
system

Eustachian tube
Middle ear
cavity

Epitympanum

Mesotympanu
m

Hypotympanu
m

Protympanum

Post-
tympanum

14. Contents of middle ear cleft

3 Ossicles : malleus, incus,
stapes

2 Nerves : Chorda tympani,
Tympanic plexus

2 Muscles :Tensor tympani,
stapedius

Air

Mucosal folds & ligaments

Blood vessels

15. ET
MEME
ATTIC
AD
Ant

16. Tympanic Membrane

Partition between the external and
middle ear

Obliquely set with 55
0
to floor

Dimension: 10 mm x 8 mm x 0.1 mm

Parts

Pars Tensa

Pars Flaccida (Shrapnel's
membrane)

17. PF
PT

18. Landmarks of TM
1.Short process
of malleus
2.Anterior and
posterior
malleolar folds
3.Handle of
malleus
4.Umbo
5.Cone of light
6.Annulus
tympanicus

19. Layers of tympanic membrane
1) Outer layer of squamous epithelium
continuous with that of the meatus
2) Middle layer of fibrous tissue that has
radial and circular fibres
3) Inner layer of mucous membrane
continuous with the lining of the
tympanic cavity
Fibrous layer disorganized in pars
flaccida
Annulus deficient superiorly as notch of
Rivinus

20. Four Quadrants of pars
Tensa
AS
AI
PS
PI

21. Borders of middle ear cavity

Roof : Tegmen tympani

Floor : Separates tympanic cavity from
jugular bulb

Medial wall

Promontory : Bulge formed by basal
turn of cochlea

Oval window : Communicates between
middle ear and the vestibule of the inner
ear, closed by footplate of stapes

Round window :Communicates between
scala tympani and tympanic cavity,
covered by secondary tympanic membrane

24. Lateral wall
Largely by TM
Scutum (outer attic wall)
Bone inferior to TM
Anterior wall
Thin plate of bone
Openings of canal for tensor tympani
and Eustachian tube
Posterior wall
Separates middle ear cavity from
mastoid bone
Contains aditus ,pyramid

25. The mastoid antrum and air cell
system
Mastoid antrum : Largest and most consistent
air cell of mastoid air cell system, well
developed at birth
Relations
Roof : Part of floor of MCF
Floor : Digastric muscle, sigmoid
sinus
Posterior: Bony covering of sigmoid sinus
Lateral : Squamous temporal bone
(corresponds to suprameatal or Macewan’s
triangle and Cymba conchae)

26. Mac Ewan’s Triangle ( Suprameatal
triangle)
•Boundaries
•Superior : Posterior prolongation of
upper border of root of zygoma
•Anterioroinferior : Posterosuperior
margin of bony external meatus
•Posteroinferior : Vertical tangent
drawn through the posterior margin of
bony external meatus touching the
first line

28. Mastoid air cell system
Extensive system of interconnecting air filled
cavities arising from walls of mastoid antrum
that extend throughout the mastoid
Lined with flattened non ciliated squamous
epithelium
Types
Cellular ( pneumatized) : Honeycomb
appearance on plain X-Ray mastoid
Diploic : Air cells interspersed with marrow
containing spaces
Acellular (sclerotic)

30. Five Recognized regions of mastoid
pneumatisation (Allam -1969)
Middle ear : Epitympanum, Mesotympanum,
Hypotympanum, Protympanum,
posterior tympanum
Mastoid: Antrum, central mastoid, peripheral
mastoid
Perilabyrinthine: Supralabyrinthine,
infralabyrinthine
Petrous apex : Apical, peritubal
Accessory : Zygomatic, squamous, occipital,
styloid

31. Inner ear

32. 
Lies in the petrous temporal bone

Divisions

Bony labyrinth

Membranous labyrinth

33. Bony labyrinth ( Vestibule,
Semicircular canals , Bony cochlea)

Vestibule

Central portion of bony labyrinth, ovoid
in shape

Oval window at the lateral wall, utricle
and saccule in the medial

Openings of SCC (5) - lie on posterior,
superior and inferior walls of bony
vestibule

35. Semicircular canals (3)
Lie in planes at right angles to
each other
Ampullated and non ampullated
ends
Ampullated ends contain
vestibular sensory epithelium and
independently open into the
vestibule

36. Bony cochlea
Coiled tube like the shell of a snail,
contains 2
½
to 2
¾
turns
Height around 5mm,base around 9
mm in diameter
Coils turn around the modiolus -
extends along the entire length of
cochlea except for helicotrema
( small channel at the apex)

37. Three compartments
Scala vestibuli
Scala tympani
Scala media (membranous cochlea)
Within the modiolus lie spiral ganglion
Cochlear nerve lies within the bony
modiolus throughout the entire length

38. Membranous labyrinth
Membranous cochlea
Triangular in cross section
Bordered by Reisner’s membrane,
Basilar membrane and stria vascularis
Utricle and saccule
Semicircular ducts
Endolymphatic ducts and sac

40. Organ of Corti
Sense organ of hearing
Situated on the basilar membrane
Components
Tunnel of Corti
Hair cells ( outer and inner)
Supporting cells (Deiter's,
Hansen's)
Tectorial membrane

42. Differences between inner and outer hair
cells
Inner Hair Cells Outer Hair Cells
3500 12,000
Single row Three or four rows
Flask-shaped Cylindrical
Primarily afferent Primarily efferent
Transmit auditory
stimuli
Modulate inner hair
cell
Resistant to damage Vulnerable to
damage