DR. MADAN JUNIOR RESIDENT

5 dictinct sesory organs : 3 semicircular canals 2 otolith organs

4th 25th week of gestation

Surface ectoderm

Otic placode

Otic pit

(30 days)

Otic vesicle / otocyst

Acoustico facial ganglion (neural crest cells : 4wks )

Vestibuolo geniculate

cochlear ganglion

otocyst

Endolymphatic lateral

diverticulum utriculosaccular

chamber

Utricular chamber sacular chamber

Utriculus scc.ducts

(35 days)

Sup. Post. Lateral

sacculus cochlea

Arrival of afferent N.endings precedes hair cells (3rd wk) common macula

Upper end : utricular macula + crista ampularis sup. & lat.SCC

Lower end : saccular macula +crista ampularis post.SCCMesoderm : otic capsule / Bony labyrinth9wks : hair cells are well developed with

synapses

Macula : 14-16wks

Cristae : 23wks

Organ of corti : 25wks

Vertical canals : 45*

Horizontal canal : 30*

Function pair

Vestibular ( scarpa’s ganglion )

SuperiorSuperior InferiorInferior Ant. & lat. Cristae Post.crista Utricular macula Saccular maculaCentral regions : large ganglion cellsPeripheral regions : small ganglion cells

Na+ K+ Ca2+ ( meq / litre )

Perilymph 140 5 .68

Endolymph 5 150 .025

Endolymph : marginal cells of stria vascularis ( deeply invaginated,Free ribosomes, vesicles , Na+K+ ATPase , adenylate cyclase ,carbonic anhydrase )

Dark cells of crista & macula have similar characters.

Endolymphatic sac : columnar cells for absorption

Perilymph : ultrafiltrate of either CSF CSF or bloodblood . Reaches by vestibular aqueduct or preivascular or perineural channels

Drainage is through venules & middle ear mucosa

INTERNAL AUDITORY ( LABYRINTHINE ) A.

(45%)Anterior inferior cerebellar A.

Superior cerebellar

or

Basilar A.

Rotational acceleration = semicircular canal respond in 3 planesLinear acceleration = horizontal through utricle, vertical through saccule

AMPULLA : Crista ampularis – saddle shaped ,across floor ,at right angles to long axis.

Cupula Supporting cells Blood vessels Nerve fibres

Cupula : gelatinous mass of mucopolysaccharides in keratin meshwork

Sub cupular space

Fluid –tight

Sp.gravity – 1

( post alcoholic nystagmus )

Inorganic crsytalline deposits of calcium carbonate .

0.5 – 30 µm ( 5-7 )

Sp.gravity : 2.71 – 2.94

Very small in striola region

Utricular macula : kinocilium towards striola

Saccular macula : away from striola

Actin filaments

Hair cells : supporting cells – tight junction or desmosomes

Simple & complex calyx ( striola )

Type 1 : 2 - 1:1

Crista : central & peripheral zone Modified columnar epithelial cells

In horizontal canal kinocilium is located towards utricle ,where as in vertical canals the kinocilium is placed away from the utricle

Dimorphic 70%

Bouton 20%

Calyx 10%

Aminoglycosides kill hair cells Loop diuretics and NSAIDS are hair celltoxins

Vestibular - Holds images of the seen world steady on the retina during brief head rotations

Optokinetic - Holds images of the seen world steady on the retina during sustained head rotations

Smooth pursuit - Holds the image of a moving target on the fovea

Nystagmus (quick phases) - Resets the eyes during prolonged rotation and direct gaze toward the oncoming visual scene

Saccades - Brings images of objects of interest onto the fovea

Vergence - Moves the eyes in opposite directions so that images of a single object are placed simultaneously on both foveas

Stabilizes eye in space Necessary to see while head is in motion

Stabilizes body Helps maintain desired orientation to

environment

Semicircular Canalsare angular ratesensors. Otoliths (utricle andsaccule) are linearaccelerometers

Principle 1: The vestibular system primarily drives reflexes to maintain stable vision and posture

VOR / VCR / VSR Input to autonomic centres Cerebellum Cortical areas

Vestibular deficit can thus be unmasked by very dynamic head movements

Principle 2: By modulating the non-zero baseline firing of vestibular afferent nerve fibers, semicircular canals encode rotation of the head, and otolith organs encode linear acceleration and tilt.

Principle 3: Stimulation of a semicircular canal produces eye movements in the plane of that canal. Ewald’s 1st law.

Push – pull arrangement of canals

B.P.P.V

Slow phase eye movement downward in the plane of affected pc.

Principle 4: A semicircular canal is normally excited by rotation in the plane of the canal bringing the head towards the ipsilateral side.

Horizontal : ampulopetal flow is excitatoryVertical : ampullofugal flow is excitatory

Principle 5: Any stimulus that excites a semicircular canal's afferents will be interpreted as excitatory rotation in the plane of that canal.

Vertigo Nystagmus ( brief changes )

Pc- BPPV-Exitation of PC afferent Superior canal dehiscence syndrome Caloric testing : COWS (cold opposite, warm same) –

direction of the nystagmus

Principle 6: High accelerations head rotation in the excitatory direction of a canal elicits a greater response than does the same rotation in the inhibitory direction. Ewald’s 2nd law.

Excitation inhibition asymmetry:Hair cells asymmetry. Vest.aff. baseline

firing rate 50 – 100 spikes / sec. while they can be increased they cannot be driven below 0.

Acceleration must be 3000 degrees/sec2 , and the peak velocity must be 150 to 300 degrees/sec, meaning that the rotation must be finished in 150 milliseconds , 10 to 15 degrees.

HEAD THRUST TEST

Principle 7: The response to simultaneous canal stimuli is approximately the sum of the responses to each stimulus alone

RIGHT HAND RULE

Vestibular neuronitis : Fetter & Dieghan’s et al proposed that vestibular neuritis is usually a disorder of organs innervated by sup.vestibular N. 21% occurrence of ipsilateral Pc-BPPV.

Principle 8: Nystagmus due to dysfunction of semicircular canals has a fixed axis and direction with respect to the head

Central nystagmus direction may change with direction of gaze , where as peripheral nystagmus has a fixed axis & direction.

Principle 9: Brainstem circuitry boosts low-frequency VOR performance through "velocity storage" and "neural integration.“

In humans the time constant of the decay of angular VOR for constant velocity of rotation is about 20sec longer.

Arise from medial & descending vestibular nucleus whose axons cross midline

Pre & post rotatory nystagmus (due to exitation& inhibition asymmetry net result not zero-sensed by brain stem)

Head –shake nystagmus Alexander’s law -Amp of nystagmus

Video Frenzel Goggles

Principle 10: The utricle senses both head tilt and translation, but loss of unilateral utricular function is interpreted by the brain as a head tilt toward the opposite side

Ocular tilt reactionHead tilt

Disconjugate deviation ( skew)

Counter roll

Principle 11: Sudden changes in saccular activity evoke changes in postural tone.

Activates the extensor muscles & relaxes the flexors to restore postural tone

VEMP---short latency relaxation potential by click or tone burst

Principle 12: The normal vestibular system can rapidly adjust the vestibular reflexes according to the context, but adaptation to unilateral loss of vestibular function may be slow and susceptible to decompensation

It is rhythmic repetitive oscillation of eye , initiated by a slow eye movement that drives the eye off target , followed by a fast movement that is corrective(jerky movement) or another slow eye movement in the opposite direction.(pendular nystagmus)

Jerky-direction, true , vestibular system Pendular- direction ,not true , visual

system Irregular- jerky or pendular , cns leasion

Direction –detemined by direction of fast phase.

Horizontal plane- H nystagmus , V systemVertical plane- vertical nystagmus ,CNS

First degree

Second degree

Third degree

Peripheral vestibular pathology-decrease on optic fixation & increase on optic fixation withdrawal(eye closed)

Central vestibular pathology-

Features peripheral central

Direction -fast phase away from leasion-unilateral disease of vestibular organ or nerveLabyrinthitisMeniere’s disease

-changes with gaze-disease of brain stemAny cns disorder

Visual fixation Inhibit nystagmusAlways diminishes or even disappear

Either no effect or increase nystagmus

Peripheral Central

Latency + -

Duration < 1 min > 1 min

Fatigability Yes No

Reversal with upright position

Yes No

Seasaw nystagmus –parasellar lesion(Pituitary leasion)

- rostral midbrain lesion

Multiple sclerosis Arnold chiari malformation Vertbrobasilar insufficiency Drug –alcohol, antiseizure

BPPV Medullar leasion

Mid brain anomalies---in child pineal tumor ,mid brain vascular malformation

Hind brain anomalies—chiari malformation

A sensation of spinning or motion

Time course : helps to discriminate between otologic and nonotologic causes of vertigo

Vertigo that lasts for less than 1 minute can represent benign paroxysmal positional vertigo

Vertigo that is prolonged for hours is typical of Ménière's disease or endolymphatic hydrops

Seconds to minutes to hours Perilymphatic fistula Benign paroxysmal positional vertigo Otosclerosis Vascular • Migraine • Vertebrobasilar insufficiency (AICA) • Wallenberg syndrome • Hyperviscosity syndromes

Hours: Ménière's disease Migraine Metabolic Iatrogenic Syphilis

Days:- Labyrinthitis Temporal bone trauma Iatrogenic Viral neuronitis Vertebrobasilar infarction Cerebellar/brainstem hemorrhage Autoimmune neurolabyrinthitis Multiple sclerosis

most common infectious cause of acute vertigo is viral labyrinthitis Traumatic causes of vertigo include

temporal bone fractures, labyrinthine concussion, and perilymphatic fistula

Systemic metabolic abnormalities that can affect vestibular function include hyperviscosity syndromes (hyperlipidemia, polycythemia, macroglobulinemia,sickle cell anemia), diabetes mellitus, hyperlipoproteinemia, and hypothyroidism

A number of collagen vascular disorders have been associated with vestibular dysfunction as a form of autoimmune inner-ear disease. Common disorders of this type include rheumatoid arthritis, polyarteritis nodosa, temporal arteritis,nonsyphilitic interstitial keratitis, lupus, sarcoid, relapsing polychondritis, dermatomyositis, and scleroderma.

Ischemia of small labyrinthine vessels will cause isolated infarction of the vestibular labyrinth and vertigo; occlusion of larger vessels anterior inferior cerebellar artery or its branches will cause sudden and profound loss of both auditory and vestibular function and regional infarction of the brainstem.

. Endolymphatic hydrops or Ménière's disease is defined by the well-recognized symptoms of vertigo, hearing loss, tinnitus, and aural fullness. The underlying mechanism(s) that cause abnormal homeostasis of endolymph resulting in distention and rupture of the membranous labyrinth

. Histopathologic findings suggest that fibrosis of the endolymphatic sac,

. Altered glycoprotein metabolism, . viral infections may be pathogenic

Otoconia or calcium carbonate crystals normally attached to the macula of the utricle become free floating within the endolymph of the posterior semicircular canal. These free-floating particles become gravity sensitive and cause a hydrodynamic shift in endolymph that affects the posterior semicircular canal cupula in response to provocative head movements, resulting in positional vertigo.

The peripheral vestibular system includes : (1) sensory receptor structures that are responsible both for sensing the motion and position of the head in space and converting (transducing) the sensory stimulus into an electricalsignal;

(2) the vestibular portion of the eighth cranial nerve that carries the encoded sensory information from the receptors to the central nervous system (CNS) in the form of neural activity

Ménière's disease (idiopathic endolymphatic hydrops) is a disorder of the inner ear associated with a symptom complex consisting of spontaneous, episodic attacks of vertigo; sensorineural hearing loss that usually fluctuates; tinnitus; and

often a sensation of aural fullness.

distortion of the membranous labyrinth perisaccular ischemia and

fibrosis(pathologic study) hypoplasia of the endolymphatic sac and

duct(imaging study) Autoimmune processes

Pathogenesis:1. utricular destruction2. Cupulolithiasis3. based on the fatigability of the

nystagmus

canalithiasis mechanism-latency nystagmus duration ---lowest part of

canal the vertical (upbeating) and torsional nystagmus reversal of nystagmus fatigability of the nystagmus(repeated

Dix Hallpike - dispersion of material with in the canal)

syndrome of vertigo and oscillopsia induced by loud noises or by stimuli that change middle ear or intracranial pressure

Tullio phenomenon--- eye movement-- loud noise

Hennebert's sign

"third mobile window

Loud sounds, positive pressure in the external auditory canal, and the Valsalva maneuver against pinched nostrils --- ampullofugal deflection ---nystagmus that has slow phase components that are directed upward with torsional motion of the superior pole of the eye away from the affected ear.

Conversely, negative pressure in the external canal, Valsalva against a closed glottis, and jugular venous compression ----oppositelydirected eye movements with slow phase components directed downward with torsional motion of the superior pole of the eye toward the affected ear.