Vestibular function in experimental endolymphatic hydrops.

Endolymphatic sac ablation in the guinea pig can result in a dilated membranous labyrinth and low-frequency hearing loss similar to patients with Meniere's disease. However, this animal model fails to develop analogous symptoms of a Meniere's crisis such as sudden hearing loss and marked vestibular imbalance. Possibly, factors in addition to endolymphatic hydrops must be present to result in a crisis episode. By placing animals in an inverted posture, their intralabyrinthine pressure was elevated, causing additional stress on the inner ears. Standard electronystagmographic techniques were used to monitor vestibular imbalance, which appeared as spontaneous nystagmus in the dark. Nineteen of 23 animals with unilateral endolymphatic hydrops showed spontaneous nystagmus in an inverted posture. Physiologic mechanisms explaining these results are described.