Acute endolymphatic hydrops has no direct effect on the vestibular evoked potential in the guinea pig

To investigate the effect of an acute endolymphatic hydrops on the functioning of the vestibular system a hydrops was created by microinjection of artificial endolymph through the basilar membrane into scala media in 10 guinea pigs. To control for the effect of perforation of the basilar membrane, the same procedure was performed in 9 other guinea pigs, but without injection of endolymph. Contralateral ears served as control ears. Vestibular evoked potentials, evoked by vertical acceleration pulses applied to the guinea pig's head, were measured in all ears before, immediately after, and 2, 4, and 5 hours after perforation/injection. Acute endolymphatic hydrops did not affect the amplitude of the VsEP immediately after injection. After 4 to 5 hours VsEP was significantly reduced in both hydrops and perforated-only ears, compared to control ears. However, no significant difference was found between VsEP of the hydrops ears and perforated-only ears.

Reduction of VsEP is not caused by a direct hydromechanical effect on the vestibular system, but possibly by leakage of perilymph through the perforation hole, supporting the membrane rupture theory for Meniere-attacks.