Basilar Membrane Displacement Related to Endolymphatic Sac Volume

Abstract

To demonstrate that the amount of basilar membrane displacement toward the scala tympani and its attachment to the bony wall of the scala tympani (i.e., interscalar septum) in hydropic temporal bones is related to the intraosseous endolymphatic sac volume. A retrospective analysis of temporal bones from individuals with the histopathologic diagnosis of "endolymphatic hydrops." Fifty-two temporal bones, from 38 patients, with the histopathologic findings of "endolymphatic hydrops" were analyzed microscopically. Data were obtained regarding the displacement of the basilar membrane, endolymphatic sac volume, hair cell loss, strial atrophy, ganglion cell loss, and last measured auditory thresholds. The relationships between these variables were examined statistically. Nineteen of the 52 temporal bones (36.5%) with endolymphatic hydrops showed displacement of the basilar membrane toward the scala tympani in the apical and middle segments of the cochlea. A reduced volume of the endolymphatic sac was significantly related to increased severity of basilar membrane deformation (Rho = -.646; P < or = .001). Multiple regression analysis showed that severity of basilar membrane deformation was the single best predictor of low frequency thresholds while loss of hair cells was the best predictor of pure-tone average threshold. The displacement of the basilar membrane in the apical and middle segments that may occur with endolymphatic hydrops, to the extent that it impinges on the interscalar septum, is related to a reduction in the intraosseous endolymphatic sac volume.