Differential Volume Increase of Endolymphatic Compartments in Ménière's Disease Is Inversely Associated With Membrane Thickness.

Objectives: Our aim in this study was to characterize the morphology of the endolymphatic compartment on histopathology in individuals with Ménière's disease (MD) and to determine why hydrops of the saccule is more pronounced than that of other compartments of the inner ear in MD.

Methods: Temporal bones from 9 patients with idiopathic MD and from 10 individuals without MD/endolymphatic hydrops were examined. The inner ear fluid compartments in normal ears, and ears with MD were three-dimensionally reconstructed and their volume was calculated. The thickness of the membranes of the labyrinth was measured, and both ruptures of the membranes and patency of the utriculoendolymphatic (UEV; Bast's) valve were assessed.

Results: In ears with MD, the saccule and the cochlear duct were most frequently hydropic; the utricle was involved approximately half as frequently. In ears without MD, the Reissner's membrane and the membranous wall of the saccule were thinner than that of the utricle and of the lateral semicircular canal ( p < 0.01). The lateral semicircular canal did not show signs of hydrops. In all ears with MD in which the utricle exceeded the average volume of normals (6 of 12), the UEV was open or there was a rupture in the utricle.

Conclusion: Increases in endolymphatic pressure may cause a primary swelling of the apical cochlear duct and saccule, both of which have relatively thin membranes. Hydrops in the utricle may occur less frequently because of a thicker wall, because of a functioning UEV, and when the saccule has already occupied most of the vestibular perilymphatic space.