Long-term effects of destruction of the endolymphatic sac in a primate species.

The endolymphatic sacs of ten vervet monkeys were surgically ablated unilaterally, and the animals were assigned predetermined survival times ranging from 6 months to 5 years. The left and right ears were prepared in anatomical continuity for light microscopic study. Four experimental ears had openings in their membranous labyrinths of unknown etiology and were not considered acceptable for correlative studies. The remaining five experimental ears showed mild cochlear endolymphatic hydrops, which was localized to the apical regions or was more severe in the apical regions than elsewhere. Four ears also showed saccular endolymphatic hydrops. The sensory and neural structures in both experimental and control ears were normal, and none of the control ears showed endolymphatic hydrops. None of the animals developed severe endolymphatic hydrops or the cochleovestibular symptoms that occur in human subjects with Meniere's disease. The results of this experiment indicate that dysfunction of the endolymphatic sac may be a contributing factor, but probably is not the sole cause of Meniere's disease.