Central Lesions With Selective Semicircular Canal Involvement Mimicking Bilateral Vestibulopathy

Abstract

Bilateral vestibulopathy (BVP), which is due to peripheral lesions, may selectively involve certain semicircular canal (SCC). Recent eye movement recordings with search coil and video head impulse test (HIT) have provided insight in central lesions that can cause bilateral and selective SCC deficit mimicking BVP. Since neurological signs or ocular motor deficits maybe subtle or absent, it is critical to recognize central lesions correctly since there is prognostic and treatment implication. Acute floccular lesions cause bilateral horizontal SCC (HC) impairment while leaving vertical SCC function unaffected. Vestibular nuclear lesions affect bilateral HC and posterior SCC (PC) function, but anterior SCC (AC) function is spared. When both eyes are recorded, medial longitudinal fasciculus lesions cause horizontal dysconjugacy in HC function and catch-up saccades, as well as selective deficiency of PC over AC function. Combined peripheral and central lesions may be difficult to distinguish from BVP. Anterior inferior cerebellar artery stroke causes two types of deficits: 1. ipsilateral pan-SCC deficits and contralateral HC deficit and 2. bilateral HC deficit with vertical SCC sparing. Metabolic disorders such as Wernicke encephalopathy characteristically involve HC but not AC or PC function. Gaucher disease causes uniform loss of all SCC function but with minimal horizontal catch-up saccades. Genetic cerebellar ataxias and cerebellar-ataxia neuropathy vestibular areflexia syndrome typically do not spare AC function. While video HIT does not replace the gold-standard, search coil HIT, clinicians are now able to rapidly and accurately identify specific pattern of SCC deficits, which can aid differentiation of central lesions from BVP.

Video head impulse test (v-hit) em indivíduos com diabetes mellitus tipo 1

“…The semicircular canals (SC) detect angular movements of the head, through the vestibulo-ocular reflex (VOR), while the saccule and utricle detect the linear accelerations of the head, in addition to head-tilts in space (17)(18)(19)(20) . The VOR is responsible for maintaining a clear image on the retina during head movements, triggering compensatory eye movements in the opposite direction (20,21) .…”

“…The semicircular canals (SC) detect angular movements of the head, through the vestibulo-ocular reflex (VOR), while the saccule and utricle detect the linear accelerations of the head, in addition to head-tilts in space (17)(18)(19)(20) . The VOR is responsible for maintaining a clear image on the retina during head movements, triggering compensatory eye movements in the opposite direction (20,21) . Previous studies used the caloric test to assess the vestibular function of individuals with diabetes mellitus, but, currently, this analysis can be performed in an objective and detailed way, through the assessment of the vestibulo-ocular reflex using the Video Head Impulse Test (v -HIT) (22)(23)(24)(25) .…”

Video Head Impulse Testing: From Bench to Bedside

“…It holds great promise in the acute differentiation of acute posterior circulation stroke from unilateral peripheral vestibulopathy [19][20][21] based on search coil recording, which has unequivocally demonstrated the diagnostic value of gain and catch-up saccade analysis. 22 Many vestibular disorders, both peripheral [23][24][25] and central, [26][27][28] rapidly evolve over time and have known specific treatments and can now be reassessed without subjecting patients to repeated lengthy testing. As both lateral and vertical SCCs can be evaluated, different patterns of SCC involvement have emerged that carry diagnostic significance: selective sparing of AC function has been demonstrated to be specific for certain causes of bilateral vestibulopathy (BV), 29 whereas selective impairment of PC function is uncommon and usually associated with additional audiovestibular loss.…”

“…58,59 Clinical differentiation of central from peripheral vestibulopathies in AVS may be time-critical, for example, "ruling out a stroke," but is not always straightforward. 28 This is obviously important from a prognostic and therapeutic perspective. 60,61 The traditional teaching is that clinical HIT is normal or negative in central vestibulopathy.…”

“…73 Second, there is less AC sparing, probably due to three different mechanisms: on-off direction asymmetry in the vertical SCC plane, property of the secondary neurons (easily silenced because of lower resting rate, higher sensitivity to rotation), and relative strength of extra-MLF pathway carrying AC signal. 28 There are two important clinical points since current vHIT devices only record one eye. First, consider a left eye vHIT system: in unilateral INO, if the MLF lesion is on the left, then during left LC impulses, there will be reduction in VOR gain, recording from the adducting left eye, and during right LC impulses, VOR gain will be normal, recording from the abducting left eye.…”