Anatomy of ear and mastoid

1. Anatomy of ear and
mastoid
Dr. Krishna Koirala
Dr. Krishna Koirala // Anatomy of Ear and Mastoid

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 subdivisions are involved in hearing
• Inner ear is involved in body balance and equilibrium

3. External Ear (Outer Ear)

4. 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 TM
− Protect the tympanic membrane
• Importance : Perichondrium/cartilage used as a graft material
for middle ear and other reconstructive surgeries

5. Parts of pinna
 Helix: Slightly curved rim of the
auricle
 Antihelix: Broader curved eminence
anterior to helix
 Concha : Deep cavity in front of the
antihelix
• Cymba conchae : Depression between the antitragus and
ascending crus of the helix (surface landmark of mastoid antrum)
• Tragus: prominence in front of and partly closing the external
auditory canal
• Lobule : lower portion of pinna made up of areolar tissue & fat without cartilage

6. 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

7. External Auditory canal

8. • 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

9.  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

10. Middle Ear

11. Middle ear cleft
 Contents
− Middle ear cavity
− Attic ,aditus, antrum
− Mastoid air cell system
− Eustachian tube
 Develops from tubo -tympanic
recess
Middle ear cavity
 Epitympanum
 Mesotympanum
 Hypotympanum
 Protympanum
 Post- tympanum

12. ET
ME
ATTIC
AD
Ant

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

14. Tympanic Membrane
• Partition between the external and middle ear
• Obliquely set with 550 to floor
• Dimension: 10 mm x 8 mm x 0.1 mm
• Parts
– Pars Tensa
– Pars Flaccida (Shrapnel's membrane)

15. PF
PT

16. • Landmarks of TM
– Lateral process of malleus
– Anterior and posterior
malleal folds
– Handle of malleus
– Umbo
– Cone of light
– Annulus tympanicus

17. • 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

18. Four Quadrants of pars Tensa
AS
AI
PS
PI

19. 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

21. • 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

22. 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)

23. Mac Ewan’s Triangle (Suprameatal Triangle)
• Boundaries
− Superior : Posterior prolongation of upper border of root of
zygoma (Supramatoid crest)
− Anteroinferior : Posterosuperior margin of bony external
meatus
− Posterior: Vertical tangent drawn through the posterior
margin of bony external meatus to the first line
• Contains spine of Henle
• Surgical landmark for mastoid antrum (Mastoid antrum lies 1.5
- 2.0 cm deep to the triangle in adults)

25. 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)

27. 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

28. Inner ear

29.  Lies within the petrous temporal bone
 Divisions
 Bony labyrinth : consists of a series of bony cavities within
the petrous temporal bone
 It is composed of cochlea, vestibule and semi-circular
canals. These structures are lined internally by periosteum
and contain perilymph
 Membranous labyrinth: lies within the bony labyrinth. It
consists of the cochlear duct, utricle, saccule and semi-
circular ducts and is filled with endolymph

30. 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

31. Pink= Endolymph
Blue= Perilymph

32.  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
− Non ampullated end of lateral SCC opens
separately whereas those of superior and posterior
SCCs join to form crus commune before opening in
the vestibule

33. 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)

34.  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

35. Membranous labyrinth
 Membranous cochlea
− Triangular in cross section
− Bordered by Reissner's membrane, Basilar
membrane and stria vascularis
 Utricle and saccule
 Semicircular ducts
 Endolymphatic ducts and sac

37. 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

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