Figure 7.

Mechanism of canalolithiasis of bilateral geotropic horizontal canal BPPV (the involved horizontal canal sare colored black). (a) Patient in supine position with debris in the posterior part of both horizontal canals. (b) Supine roll test on either side would result in excitation of the horizontal canal of the lowermost ear, due to ampullopetal endolymph flow and at the same time inhibition of the horizontal canal of the uppermost ear, due to ampullofugal endolymph flow. Vectorial summation would result in an intense, symmetric geotropic nystagmus.