Figure 8.

Mechanism of cupulolithiasis of bilateral apogeotropic horizontal canal BPPV (the involved horizontal canals are colored black). (a) Patient in supine position with debris adherent to the cupula of both horizontal canals. (b) Supine roll test on either side would result in inhibition of the horizontal canal of the lowermost ear, due to ampullofugal (inhibitory) deflection, triggering an apogeotropic horizontal nystagmus. At the same time, excitation of the horizontal canal of the uppermost ear would occur, due to ampullopetal (stimulatory) deflection of the cupula. Vectorial summation would result in an intense, more or less symmetric, apogeotropic nystagmus.