Objective Measurement of the Human Endolymphatic Sac Dimensions in Ménière's Disease

Abstract

To identify structural differences between the endolymphatic sac of temporal bones with and without Ménière's disease by applying design-based stereology. The dimension of the human endolymphatic sac has previously been studied by extrapolating 2-dimensional irregularities on the sectional level into 3-dimensional quantities via unfolding algorithms. These computer renderings require certain geometrical assumptions of the object studied. The term design-based used in the present study signifies that the methods and sampling schemes are defined a priori, in such a manner that consideration of the size, shape, spatial orientation, and distribution of the investigated structures are eliminated. Archival materials of 15 human temporal bones with Ménière's disease and 15 control specimens were investigated by design-based stereology. The total surface area of the endolymphatic sac was significantly lower in the Ménière's disease group (24.8 mm) compared with the control group (47.0 mm), p = 0.006. The volume fraction of the homogenous substance was significantly higher in the Ménière's disease group (17.5%) compared with the control group (5.7%), p = 0.031. No significant differences were found between the volumes of the homogenous substance, the volumes of the endolymphatic sac, and the surface-to-volume ratio in the 2 groups. The study revealed a large biological variation. Design-based stereology is a robust, unbiased and efficient tool to quantify 3-dimensional structures derived from 2-dimensional histologic sections. A 2-fold reduction in the surface area of the endolymphatic sac and a 3-fold increase in the volume fraction of homogenous substance in temporal bones with Ménière's disease may, at least in part, be involved in the dysfunction of endolymph fluid homeostasis and the development of endolymphatic hydrops.