L13: anatomy of the ear Flashcards
Explain why referred pain from other head and neck structures can involve the ear
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
Describe the anatomy of the external ear
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
Describe the self-cleaning function of the external acoustic meatus
Desquamation and skin migration laterally off tympanic membrane out of the canal = epithelial migration
Describe a pinna haematoma
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
Describe perichondritis
Inflammation of the perichondrium (coats the surface of the cartilage)
Looks red and sore
Describe how wax can affect the external acoustic meatus
If wax is impacted -> sound waves travelling to the tympanic membrane can be blocked
Describe otitis externa
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
Describe acute otitis media
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
Describe otitis media with effusion
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
Describe cholesteatoma
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
Describe the anatomy of the middle ear
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
Describe the acoustic reflex
Tensor tympani and stapedius contract if there is excessive vibration due to loud noise
Protective
Describe otosclerosis
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
Describe how pressure is equilibrated in the middle ear
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
Why is middle ear infection more common in infants?
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
List complications of acute otitis media
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
Describe the anatomy of the inner ear
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
Describe the cochlea’s role in hearing
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
Describe how we hear
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
Describe the vestibular apparatus
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
Describe presbycusis
Sensorineural hearing loss associated with old age
Bilateral and gradual
Describe benign paroxysmal positional vertigo
Vertigo only
Short-lived episodes (seconds); triggered by movement of head
Describe Ménière’s disease
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
Describe acute labyrinthitis
History of upper respiratory tract infection
Involvement of all inner ear structures, associated with hearing loss/tinnitus, vomiting and vertigo
Describe acute vestibular neuronitis
History of upper respiratory tract infection
Sudden onset of vomiting and severe vertigo (lasting days)
Usually NO hearing disturbance or tinnitus
List conditions which result in conductive hearing loss
Pathology involving the external/middle ear Wax Acute otitis media Otitis media with effusion Otosclerosis
List conditions with result in sensorineural hearing loss
Pathology involving the inner ear structures or CN VIII Presbycusis Noise-related hearing loss Meniere’s disease Ototoxic medications Acoustic neuroma
Explain the steps involved in examining the external ear and external auditory meatus using an otoscope
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
Explain the steps involved in examining the tympanic membrane using an otoscope
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
Describe the Weber’s test
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)
Describe the findings of a Weber’s test
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
Describe the Rinne’s test
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
Describe the findings of a Rinne’s test
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
