Endolymphatic pseudohydrops of the cochlear apex.

Abstract

To demonstrate that what appears to be endolymphatic hydrops of the apical scala media is normal anatomy. Computer-generated three-dimensional reconstruction of the cochlear apex and tabulation of the number of cases with arched Reissner's membranes (pseudohydrops) versus flat membranes. Temporal bone laboratory consisting of 809 documented pairs of temporal bones. Archival temporal bone sections from 107 bones (65 patients) were used to determine the percentage of arched (pseudohydrops) versus flat Reissner's membranes. Two bones, one of each membrane shape, were randomly selected for computer-generated three-dimensional reconstructions showing the cochlear apical anatomy. An arched Reissner's membrane was found in 48.6 percent of bones. In the cochlear apex, Reissner's membrane appears to be distended, simulating hydrops, due to its transition from a conical structure to a triangle bounded by the basilar membrane with the organ of Corti, the stria vascularis, and Reissner's membrane. Membrane findings were similar in both ears in 73.8 percent of the bilateral cases studied. There were no significant relationships between membrane type and clinical characteristics. What appears to be endolymphatic hydrops of the cochlear apex is the transition area of the cochlear duct from a conical shape at the extreme apex to the triangular shape found in the rest of the cochlea. The appearance of distension is dependent upon the cochlear length and the level of the microscopic section.