This document outlines the embryology, anatomy, physiology, and tests related to the vestibulocochlear system. It discusses: - The embryological origin of the vestibulocochlear system from the ectoderm and pharyngeal pouches. - The anatomy of the bony and membranous labyrinths, cochlea, vestibular system and cranial nerve VIII. - The physiology of hearing which involves vibration transmission through the ossicles and stimulation of hair cells. - Subjective and objective tests used to evaluate hearing and vestibular function, including tuning fork tests, audiometry, and vestibular tests like calorics and nyst

1. Dr.Mumtaz ali
JPMC KARACHI

2. Outlines
 Embryology
 Anatomy
 Physiology
 Tests
 D/D

3. Embryology
 vestibulocochlear : ectoderm.
 neurosensory epithelial structures : petrous portion of
the temporal bone
 encased in the otic capsule.
 the middle ear space : first pharyngeal pouch
 the external ear : overlying epithelium,

4. Anatomy
 VIII CN : cochlear + vestibular nerves.
 neurons of these primary afferent nerves : bipolar
 dendrites : the inner and outer hair cells
 vestibulocochlear labyrinth : complex of bony spaces : the
bony labyrinth
 perilymph ( CSF)
 the membranous labyrinth : endolymph
 The cochlea :anteriorly
 vestibular labyrinth by the vestibular, cochlear, and facial
nerves
 The vestibular : posterior to the cochlea

6. Vestibulo-Chochlear system
The cochlea (snail ) : hollow tube : 2.5
times over a distance of 33 mm.
base : anterior part of the fundus of the
IAC
oval window : superiorly & faces : laterally and
footplate of the stapes
round window : inferiorly & faces posteriorly

7. The scala media : endolymph
the scala vestibuli : Reissner’s
membrane
Scala tympani :basilar membrane
The scala vestibuli & scala
tympani:perilymph
scala vestibuli : the oval window
scala tympani : round window.
basilar membrane : widest :
helicotrema
narrowest : base
Maximal high-frequency vibration :
base
maximal low-frequency vibration
:apex
The organ of Corti consists :
single row of inner hair cells
three rows of outer hair cells.

13. Physiology of hearing
 Air vibrations impinge =>tympanic membrane =>
malleus to vibrate => incus => stapes => footplate =>
fluids of the labyrinth => stimulus along the basilar
membrane => organ of Corti.
 Impulses => cochlear nerve endings => cochlear nuclei
in pontomedullary junction => auditory areas of the
cortex

14. Physiology of vestibular system
 vestibular receptors => head acceleration and gravity
=>biologic signal
 CNS => data => subjective awareness
 afferent vestibular input => Motor reflexes =>gaze and
posture are generated

15. Subjective measures of hearing
 Tunning forks (Weber & Rinne’s) test
 Pure tone Audiometry:
 Air conduction
 Bone conduction
 Masking
 Speech audiometry
 Speech recognition threshold
 Speech recognition measures

16. Objective measures of hearing
 Immetance studies:
 Tympanometry
 Acoustic reflex
 Auditory brain stem evoked response
 Auditory neuropathy
 Electrical evoked auditory potentials with chochlear
implant users
 Otoaccoustic emission measures

17. Subjective tests of vestibular
function
 Spontaneous nystagmus
 Labyrinthine fistula test
 Positional test

18. Objective tests of vestibular
Function
 Electronystagmography
 Bithermal caloric test
 Gaze test
 Positional test
 Hallpike manuvre
 Saccade test
 Pursuit tests
 Rotational test
 Visual vestibular interaction

19. Tunning fork(Rinne & Weber test)
 Before audiometer, assessment of hearing => tuning fork tests
=>the initial assessment of Hearing loss
 Each tuning fork => pure tone => frequency =>(i.e., mass and
inertia)
 The Rinne test: air conduction VS bone conduction sensitivity.
 normal-hearing & sensorineural hearing loss :air conduction
>bone conduction
 The Weber test : the ear to which the auditory signal referred
 both ears are normal or abnormal : center of the head.
 unilateral middle ear (conductive) loss : Affected ear
 unilateral sensorineural loss : unaffected ear

20. Pure Tone Audiometry
Pure tone Air Conduction test :
 Pure-tone threshold hearing sensitivity => subjective
procedure =>
 (ANSI) =>audiometers.
 artificial ear. =>average human ear at the plane of the
tympanic membrane.
 Hearing loss (by air conduction) =>the magnitude (in
decibels) =>the 0-dB hearing level (HL)
 between 250 and 8000 Hz.
 between 8000 and 16,000 Hz
 Initial test => subjective hearing loss
 various auditory sites lesions

21. Pure tone Bone Conduction test:
 conductive vs sensorineural hearing loss = air
conduction vs bone conduction thresholds
 air conduction threshold = conductive + sensorineural
 bone conduction = sensorineural

23. Masking:
 It is defined by ANSI as the amount by which
the threshold of audibility of a sound is raised
by the presence of another (masking) sound.
 Overmasking occurs when masking stimulus from the
nontest ear crosses intracranially
to the test ear to raise the threshold of that ear
 additional diagnostic information on the
functional status of the middle ear

24. Spontaneous Nystagmus
 Frenzel lenses(14- to 20-diopter)
 eliminate visual fixation and magnify the patient’s eyes
 facilitate objective assessment of eye movement
 diagnostic and localizing

25. Labyrinthine fistula test
 compressing the air in the external auditory canal with
a pneumatic otoscope.
 Positive : conjugate deviation of the eyes opposite side.
 perforated tympanic membrane
 Vertigo
 chronic suppurative otitis media

32. Meniere’s disease
 endolymphatic hydrops
 an idiopathic condition of the membranous labyrinth
 spontaneous bouts of prolonged vertigo, fluctuating
hearing loss, and tinnitus.
 excessive endolymph within the scala media
 ages of 30 and 60 years
 more common in women
 low-sodium diet & diuretics
 labyrinthectomy or vestibular neurectomy

33. Secondary endolymphatic hydrops
 Endolymphatic hydrops : vertiginous symptoms
 seen in : otosclerosis, Cogan’s syndrome & congenital
syphilis.
 usually respond well to medical treatment.
 Cogan’s syndrome => nonsyphilitic interstitial keratitis
=> vestibular and cochlear deficits.
 eye pain, failing vision, vertigo, tinnitus & hearing loss
 requires a cochlear implant for rehabilitation

34. Vestibular neuritis
 onset of sustained & severe vertigo, made worse with
head movements.
 middle age.
 generally unilateral.
 various degrees of severity
 viral infection of Scarpa’s ganglion

35. Post-traumatic vertigo
 temporal bone:
 peripheral vestibular dysfunction:
temporal bone fracture
labyrinthine concussion
posttraumatic
positional vertigo
perilymph fistulas
 Central vestibular dysfunction:
dizziness secondary to brainstem trauma
postconcussion syndrome

36. Drugs induced ototoxicity
 Antibiotics:
streptomycin
dihydrostreptomycin
neomycin
kanamycin
gentamicin
 Chemotherapeutic
 diuretic agents

37. Guidelines for use of ototoxic drugs
 1. lifesaving measures
 2. ototoxic potential of drug & early symptoms of toxicity.
 3. milligram-per-kilogram basis.
 4. impaired renal function and in the elderly.
 5. Keep patients well hydrated.
 6. Avoid using more than one ototoxic drug at a time.
 7. Avoid ototoxic drugs in patients with existing end-organ
disease.
 8. evaluation before therapy
 9. Evaluate the patient during therapy with the same tests
 10. Discontinue use of the drug at the onset of toxicity.

38. Brainstem lesion
 Primary brain tumors :gliomas
usually grow slowly
brainstem nuclei and fiber tracts
adults :1%
children they are 5 to 10 times more common.
Vestibular and cochlear signs and symptoms : 50%
 Tumors => fourth ventricle =>vestibular
medulloblastomas
ependymoma
papillomas
teratoma
epidermoid cysts
cysticercosis.

39. Multiple sclerosis
 Vertigo is the initial symptom :5%
 During course of disease : 50%
 Hearing loss : 10% of patients
 loss : acute (hours to days) & subacute (over a period
of months)
 slowly progressive.
 Remission is common
 Plaque : MRI
 Diplopia, weakness,numbness, and ataxia

40. Migraine
 vascular disorder
 Vasodilation : headache
 Vasoconstriction : neurological symptoms
 Basilar artery migraine => CNS supplied by the posterior
circulation.
 (topiramate [Topamax], 25 to 50 mg at bedtime)
 tricyclic antidepressants ( nortriptyline [Pamelor], 10 to 150
mg
 calcium channel blockers ( verapamil [VerelanPM], 120 mg
at bedtime)
 beta blockers (e.g., propranolol,0.5 mg/kg twice daily in a
divided dose)

41. Vascular Accident
 ipsilateral vertebral artery : lateral medullary
infarction (i.e., Wallenberg’s syndrome)
 vertigo, nausea, vomiting, intractable hiccoughing,
ipsilateral facial pain, diplopia, dysphagia, and
dysphonia.
 ipsilateral Horner syndrome’s
 Ipsilateral loss of pain & tempreture on face &
contralateral loss on body
 ipsilateral paralysis of the palate, pharynx, and larynx

42.  AICA :infarction dorsolateral pontomedullary region
and the inferior lateral cerebellum
 Labyrinthine artery arise : AICA (80-90%)
 Infarction of membraneous labyrinth is common
 severe vertigo, nausea, and vomiting
 unilateral hearing loss, tinnitus, and facial paralysis.
 vertebral artery, PICA , AICA : cerebellar infarction
without brainstem involvement.

43. Tumors of posterior fossa
 persistent disequilibrium, ataxia, or vertigo
 Acoustic neuromas (vestibular schwannomas)
 Meningiomas
 epidermoid cysts
 cholesterol granulomas
 neurofibromas

44. THANK YOU