Figure 14.

(A) Presenting vHIT data for subject # 18 affected by right apogeotropic PSC-BPPV showing selectively impaired VOR-gain values for right PSC (0.47) with both covert and overt saccades. (B) Even in this case, otoliths are partially entrapped within a narrow tract of the non-ampullary branch of the canal nearly aligning with the horizontal axis, explaining the lack of spontaneous nystagmus. Likewise ASC, even in this condition the canal is thought to be partially plugged by otoconia, explaining high-frequency VOR-gain impairment for the involved canal. (C) Once diagnostic head hanging position is obtained, gravity vector should slowly move debris toward the ampullary tract of the canal below, leading to an ampullopetal endolymphatic flow (black arrow). Resulting cupular bending (red arrow) should generate an inhibitory discharge for PSC afferents, accounting for pDBN. (D) vHIT measurement following CRP for apogeotropic PSC-BPPV confirming complete restoration for the impaired PSC VOR-gain. BPPV, benign paroxysmal positional vertigo; CRP, canalith repositioning procedure; HSC, horizontal semicircular canal; LA, left anterior; LL, left lateral; LP, left posterior; pDBN, positional downbeat nystagmus; PSC, posterior semicircular canal; RA, right anterior; RL, right lateral; RP, right posterior; vHIT, video-head impulse test; VOR, vestibulo-ocular reflex.