Post on 21-May-2015
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.