anatomy of ear & mastoid dr. vishal sharma. embryology
TRANSCRIPT
Anatomy of Ear & Mastoid
Dr. Vishal Sharma
Embryology
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
Parts of ear
External Ear
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
Nerve supply of E.A.C.
Middle ear cleftConsists of:
• Eustachian tube
• Tympanic cavity (middle ear)
• Aditus
• Mastoid air cell system
• Develops from tubo-tympanic recess
Middle Ear
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
Otoscopic view
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
Walls of middle earRoof: 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)
Lateral wall
• Membranous:
a. Tympanic membrane
• Bony
a. Lateral attic wall above pars flaccida (Scutum)
b. Lateral wall of hypotympanum
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
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
Sinus Tympani
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
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
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
Eustachian Tube
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
Parts
• Lateral 1/3 is bony
• Medial 2/3 is fibro-
cartilaginous.
• Junction b/w 2 parts
is isthmus, narrowest
part of Eustachian
Tube.
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.
Adult vs. Child (< 7 yr)ADULT 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
Adult vs. Child (< 7 yr)
Functions1. 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
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
Inner Ear
Cochlear Hair Cells
Inner Hair Cells Outer Hair Cells3500 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
Vestibular Hair Cells
Temporal Bone
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 12-15 mm deep to triangle
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
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
Facial Nerve
Thank You