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

Abstract

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.

Fig. 1.

Example of a three-dimensional reconstruction of two inner ear fluid spaces and nerves (view from superior). Upper panel Left: Ear with endolymphatic hydrops. Right: unaffected normal ear. White: facial nerve; red: cochlear duct; yellow: nerves; green: utricle and semicircular canals (the superior semicircular canals are missing; blue: saccule; lilac: endolymphatic duct and sac; grey (semitransparent): total bony labyrinth (perilymphatic) space. On the left side the hydropic saccule distends into the posterior part of the bony lateral semicircular canal. In this case the volume increases compared to the normal side are: utricle 1.2 times; saccule 7.6 times; cochlear duct 3.5 times. Lower panels: The same ears without the perilymphatic space and nerves (Left: view from superior; right: view from inferior) Calibration bar: 5 mm

Fig. 2

Examples of hydropic ears compared to an ear with a normal endolymphatic space (A). B.) Isolated cochlear hydrops (1/12 cases); C.) isolated saccular hydrops (1/12 cases); D.) Hydrops in the cochlea + saccule (4/12 cases); D.) Hydrops in the cochlea + saccule + utricle (5/12 cases). Color code: green: utricle and semicircular canals (the superior semicircular canals are missing; blue: saccule; lilac: endolymphatic duct and sac; grey (semitransparent): perilymphatic space.

Fig. 3.

Light microscopic images of normal endolymphatic membranes using the same magnification. RM: Reissner’s membrane (apical turn of the cochlea); Sac.M: membrane of the saccule; Utr.M: utricular membrane; Lat.C.M: lateral canal membrane Calibration bar: 0.2 mm

Fig. 4.

Average volume difference (in percentage) of the inner ear fluid compartments in MD plotted against membrane thickness of the same fluid compartments respectively (cases with MD; two cases, in which the utricle and saccule were broadly connected, are omitted). 100%: no volume difference. Vertical dashed lines: average membrane thickness in 16 ears of normal controls. RM: Reissneŕs membrane, SCC semicircular canal