1. Anatomy of Ear & Mastoid
Dr. Vishal Sharma

2. Embryology

12. Parts of ear External ear:  Pinna / auricle  External auditory canal
Middle ear cleft:  Eustachian tube
 Tympanic cavity (middle ear)
 Mastoid air cell system
Inner ear (labyrinth):  Cochlea
 Vestibule
 Semicircular canals

13. External Ear

18. External auditory canal
24 mm long; Lateral 1/3 Cartilaginous (8 mm): up + back + medial. Medial 2/3 Bony (16 mm): down + forward + medial. Pinna pulled up + back + lateral to straighten external auditory canal.
Only cartilaginous skin has hair follicles: furuncle
Cartilaginous fissure of Santorini & bony foramen of Huschke: passage of infection to and from parotid gland

20. Nerve supply of E.A.C.

21. Middle ear cleft Consists of: Eustachian tube
Tympanic cavity (middle ear)
Aditus
Mastoid air cell system
Develops from tubo-tympanic recess

25. Middle Ear

26. Tympanic membrane Pearly white semi-translucent membrane
Obliquely placed at 550 to floor
2 parts: pars tensa and pars flaccida
3 layers of pars tensa: outer epithelial, middle fibrous & inner mucosal
Fibrous layer disorganized in pars flaccida
Annulus deficient superiorly as notch of Rivinus

30. Otoscopic view

32. 1. Epitympanum: Bounded laterally by scutum + pars flaccida & medially by bone above tympanic part of facial nerve
2. Mesotympanum: Middle ear cavity lying opposite pars tensa & bony tympanic annulus
3. Hypotympanum: Middle ear cavity below level of bony tympanic annulus
4. Posterior tympanum: Middle ear cavity behind bony tympanic annulus
5. Anterior tympanum or Pro-tympanum: Middle ear cavity in front of bony tympanic annulus

34. Walls of middle ear Roof: Tegmen tympani, middle cranial fossa
Floor: Jugular bulb, carotid artery
Anterior: Tensor tympani, ET orifice, carotid artery
Posterior: Aditus, fossa incudis, pyramidal eminence, facial recess, sinus tympani
Lateral: Tympanic membrane, scutum
Medial: Promontory, oval window, round window, lateral SCC, facial nerve (tympanic part)

38. Lateral wall Membranous: a. Tympanic membrane Bony
a. Lateral attic wall above pars flaccida (Scutum)
b. Lateral wall of hypotympanum

44. Posterior wall Aditus ad antrum
Fossa incudis for short process of incus
Bulge produced by lateral semicircular canal
Pyramidal eminence for stapedius tendon
Bulge produced by vertical part of facial nerve
Sinus tympani
Facial recess

50. Sinus Tympani Boundaries: Superior: Ponticulus Inferior: Subiculum
Lateral: Mastoid Segment of Facial Nerve
Medial: Posterior semicircular canal
It evades direct surgical visualization during surgery. Site for cholesteatoma recurrence

52. Anterior wall Chorda tympani nerve exits via canal of Huguier
Canal for tensor tympani on top
Eustachian tube opening below
Internal carotid artery is related inferiorly

56. Medial wall Lateral semicircular canal
Tympanic part of bony facial nerve canal
Processus cochleariformis
Promontory: formed by basal turn of cochlea
Oval window
Round window

60. Contents of middle ear Air 3 ossicles: malleus, incus and stapes
2 muscles: tensor tympani & stapedius
2 nerves: chorda tympani & tympanic plexus
Mucosal folds & ligaments
Blood vessels

68. Eustachian Tube

69. Anatomy 36 mm long in adults
Directed anteriorly, inferiorly & medially from anterior wall of M.E., forming angle of 450 with horizontal & sagittal planes
Enters naso-pharynx 1.25 cm behind posterior end of inferior turbinate

73. Parts Lateral 1/3 is bony Medial 2/3 is fibro-cartilaginous.
Junction b/w 2 parts is isthmus, narrowest part of Eustachian Tube.

74. Anatomy of medial 2/3rd
Cartilage plate lies postero-medially & consists of medial + lateral laminae separated by elastin hinge. Fibrous tissue + Ostmann’s fat pad lie antero-laterally.

75. Adult vs. Child (< 7 yr)
INFANT
Length
36 mm
18 mm
Angle with horizontal
45 0
10 0
Lumen
Narrower
Wider
Angulation at isthmus
Present
Absent
Cartilage
Rigid
Flaccid
Elastic recoil
Effective
Ineffective
Ostmann’s fat
More
Less

76. Adult vs. Child (< 7 yr)

77. Functions 1. Ventilation & maintenance of atmospheric
pressure in middle ear for normal hearing
2. Drainage of middle ear secretions into
nasopharynx by muco-ciliary clearance, pumping action of Eustachian tube & presence of intra-luminal surface tension

78. Functions 3. Protection of middle ear from:
Ascending nasopharyngeal secretions due to narrow isthmus & angulation between 2 parts of E.T. at isthmus
Pressure fluctuations
Loud sound coming through pharynx

80. Inner Ear

103. Cochlear Hair Cells

104. Transmit auditory stimuli Modulate inner hair cell
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

108. Vestibular Hair Cells

115. Temporal Bone

118. MacEwen’s Triangle Superior: supramastoid crest
Anterior: postero-superior margin of bony external auditory canal opening
Posterior: tangent drawn to mid-point of posterior wall of external auditory canal
Contains spine of Henle
Mastoid antrum lies mm deep to triangle

122. Trautmann’s triangle Boundaries Superiorly: superior petrosal sinus
Posteriorly: sigmoid sinus
Anteriorly: solid angle (semi-circular canals)
Pathway to posterior cranial fossa from mastoid cavity & vice versa

123. Mastoid cells Central group Accessory group
 Mastoid antrum  Squamous
 Peri-antral  Occipital
Peripheral group  Styloid
 Dural  Peri-tubal
 Sino-dural  Zygomatic
 Peri-sinus  Petrous apex
 Tip
 Retro-facial

127. Facial Nerve

136. Thank You