L13: anatomy of the ear

Question 1

Explain why referred pain from other head and neck structures can involve the ear

Answer 1

Many nerves carry general sensation from ear
Branches of cervical spinal nerves, vagus, trigeminal, glossopharyngeal
Otalgia with a normal ear examination = suspect an alternative site of pathology

Question 2

Describe the anatomy of the external ear

Answer 2

Pinna – cartilage, skin & fatty tissue
External auditory meatus – keratinising, stratified squamous epithelium (sigmoid shape)
-cartilaginous (outer 1/3) and bony (inner 2/3)
-cartilaginous part is lined with hair, sebaceous & ceruminous (produce ear wax) glands
Lateral surface of tympanic membrane
Collects, transmits & focuses sound waves onto the tympanic membrane

Question 3

Describe the self-cleaning function of the external acoustic meatus

Answer 3

Desquamation and skin migration laterally off tympanic membrane out of the canal = epithelial migration

Question 4

Describe a pinna haematoma

Answer 4

Accumulation of blood between cartilage and its overlying perichondrium from blunt injury
Common in contact sports
Subperichondrial haematoma – deprives cartilage of blood supply + pressure necrosis of tissue
Treatment = drainage & prevent re-accumulation/re-apposition of two layers
Untreated -> fibrosis, new asymmetrical cartilage development = CAULIFLOWER DEFORMITY

Question 5

Describe perichondritis

Answer 5

Inflammation of the perichondrium (coats the surface of the cartilage)
Looks red and sore

Question 6

Describe how wax can affect the external acoustic meatus

Answer 6

If wax is impacted -> sound waves travelling to the tympanic membrane can be blocked

Question 7

Describe otitis externa

Answer 7

Inflammation of the external ear - most likely pathogen is pseudomonas aeruginosa
Typically present with pain & discomfort
Risk factor: moisture within the external acoustic meatus (‘swimmers ear’)
Rare but serious complication -> malignant otitis externa
-potentially life-threatening, immunocompromised inc. diabetics at risk

Question 8

Describe acute otitis media

Answer 8

Bulging of the tympanic membrane due to infection (bulges laterally (towards external ear))
Signs and symptoms include otalgia, temperature & red +/- bulging TM and loss of normal landmarks
Mostly viral aetiology, but occasionally bacterial

Question 9

Describe otitis media with effusion

Answer 9

Underlying problem is NOT infection but can predispose to
Retracted tympanic membrane (towards middle ear) – fluid and negative pressure in middle ear (decreases motility of TM and ossicles which affects hearing)
Most resolve spontaneously in 2/3 months
May persist and/or impede speech and language development/school performance – require grommets -> act to maintain equilibration of pressures

Question 10

Describe cholesteatoma

Answer 10

Retraction of pars flaccida forms a sac/pocket
-traps stratified squamous epithelium and keratin
-proliferates forming cholesteatoma
Usually secondary to chronic Eustachian tube dysfunction (negative pressure pull the pocket into the middle ear)
Painless, often smelly otorrhea +/- hearing loss
Not malignant but slowly grows & expands -> more serious consequences due to enzymatic bone destruction

Question 11

Describe the anatomy of the middle ear

Answer 11

Air filled cavity between tympanic membrane and inner ear containing ossicles
Ossicles (malleus, incus & stapes) connected via synovial joints
Amplify and relay vibrations from the TM to the oval window of the cochlea
Ossicle movement ‘tampered’ by 2 muscles – tensor tympani and stapedius

Question 12

Describe the acoustic reflex

Answer 12

Tensor tympani and stapedius contract if there is excessive vibration due to loud noise
Protective

Question 13

Describe otosclerosis

Answer 13

One of the most common causes of acquired hearing loss in young adults
Exact cause unknown
Ossicles fused at articulations due to abnormal bone growth particularly between base plates of stapes and oval window – sound vibrations cannot be transmitted effectively to cochlea
Present with gradual unilateral/bilateral conductive hearing loss

Question 14

Describe how pressure is equilibrated in the middle ear

Answer 14

Eustachian tube equilibrates pressure of middle ear with atmospheric pressure
Mucous membrane of middle ear continuously reabsorbs air in middle ear causing negative pressure
Eustachian tube allows equilibration of pressure within middle ear cavity with that of atmosphere – also allows for ventilation & drainage of mucus from middle ear

Question 15

Why is middle ear infection more common in infants?

Answer 15

Eustachian tube is shorter & more horizontal
Easier passage for infection from the nasopharynx to the middle ear
Tube can block more easily, compromising ventilation & drainage of middle ear -> increasing risk of middle ear infection & glue ear

Question 16

List complications of acute otitis media

Answer 16

Tympanic membrane perforation
Facial nerve involvement (close relationship to middle ear cavity)
Potentially life-threatening complications:
1) Mastoiditis = middle ear cavity communicates via mastoid antrum with mastoid air cells -> provides a potential route for middle ear infections to spread into the mastoid bone
2) Intracranial complications – meningitis, sigmoid sinus thrombosis & brain abscess

Question 17

Describe the anatomy of the inner ear

Answer 17

Vestibular apparatus and cochlea – fluid filled tubes
Cochlea – fluid movement generated by the stapes, converted into action potentials (in CN VIII) -> perceived as sound
Vestibular apparatus – fluid movement generated by position and rotation of head, converted into action potentials (in CN VIII) -> perceived as position sense and balance

Question 18

Describe the cochlea’s role in hearing

Answer 18

Fluid-filled tube with specialised hair cells that generate action potentials when moved
Movements at the oral window -> movement of fluid in the cochlear duct
Waves of fluid cause movement of special sensory cells (stereocilia) -> generate action potentials via CN VIII -> brain

Question 19

Describe how we hear

Answer 19

Auricle and external auditory canal funnels sound waves -> tympanic membrane vibrates
Vibration of the ossicles sets up vibrations/movement in cochlear fluid
Sensed by stereocilia in the cochlear duct
Movement of the stereocilia in organ of Corti trigger action potentials in cochlear part of CN VIII
Primary auditory cortex makes sense of the input

Question 20

Describe the vestibular apparatus

Answer 20

Includes semi-circular ducts, saccule and utricle
Moving position or rotation of head moves fluid -> bends stereocilia -> generate action potentials via CN VIII -> brain
Perceive and maintain our sense of balance

Question 21

Describe presbycusis

Answer 21

Sensorineural hearing loss associated with old age

Bilateral and gradual

Question 22

Describe benign paroxysmal positional vertigo

Answer 22

Vertigo only

Short-lived episodes (seconds); triggered by movement of head

Question 23

Describe Ménière’s disease

Answer 23

Vertigo, hearing loss & tinnitus (typically unilateral), may also describe ‘aural fullness’, nausea & vomiting
Symptoms longer lasting
Recovery in between; recurrent episodes
Hearing may deteriorate over time

Question 24

Describe acute labyrinthitis

Answer 24

History of upper respiratory tract infection

Involvement of all inner ear structures, associated with hearing loss/tinnitus, vomiting and vertigo

Question 25

Describe acute vestibular neuronitis

Answer 25

History of upper respiratory tract infection
Sudden onset of vomiting and severe vertigo (lasting days)
Usually NO hearing disturbance or tinnitus

Question 26

List conditions which result in conductive hearing loss

Answer 26

Pathology involving the external/middle ear
Wax 
Acute otitis media 
Otitis media with effusion
Otosclerosis

Question 27

List conditions with result in sensorineural hearing loss

Answer 27

Pathology involving the inner ear structures or CN VIII
Presbycusis  
Noise-related hearing loss
Meniere’s disease 
Ototoxic medications 
Acoustic neuroma

Question 28

Explain the steps involved in examining the external ear and external auditory meatus using an otoscope

Answer 28

Examiner is ideally positioned by sitting to the side of the patient, ipsilateral to the ear being examined
Inspection & palpation of the skin around the pinna, mastoid process & pinna itself
External auditory canal is straightened first, by pulling the pinna up, out and back
In a child, the canal is straightened by pulling the pinna down and back

Question 29

Explain the steps involved in examining the tympanic membrane using an otoscope

Answer 29

Should appear as a translucent, pearly grey membrane at the end of the canal
Blood vessels should be visible around the membrane & normal position of the tympanic membrane is oblique to the external canal
Handle of the malleus is seen near the centre of the tympanic membrane
Disease: colour of the tympanic membrane may be dull, red or yellow
-bulging of membrane indicates fluid/pus in the middle ear
-white plaques = tympanosclerosis

Question 30

Describe the Weber’s test

Answer 30

Place vibrating tuning fork on head/forehead in midline
Normal ear – sound heard the same on both sides if cochlea is working, sensing the sound centrally
External ambient noise reaches the cochlea via the normal route -> masks the sound coming through the bone (if everything is normal, the masking will be the same on both sides)

Question 31

Describe the findings of a Weber’s test

Answer 31

Sound lateralises to the damaged ear in conductive hearing loss (impacted wax masking the external ambient noise)
Sound lateralises to the good ear in sensorineural hearing loss

Question 32

Describe the Rinne’s test

Answer 32

Determines what side the problem is on
Place vibrating tuning fork on mastoid process -> bypasses the external and middle ear
Place vibrating tuning fork in front of auditory external meatus
Ask patients when the sound is the loudest

Question 33

Describe the findings of a Rinne’s test

Answer 33

Normal: sounds a lot louder when placed in front of the ear
If external/middle ear problem (conductive hearing loss): bone conduction > air conduction, so sounds louder when fork is placed on mastoid process