Histology of the Cochlear Outer Sulcus Cells in Normal Human Ears, Presbycusis, and Menière's Disease.

Abstract

Outer sulcus cell features and distribution are hypothesized to differ throughout regions of the human cochlea and between diseased and normal specimens. Outer sulcus cells play a role in inner ear fluid homeostasis. However, their anatomy and distribution in the human are not well described. Temporal bone specimens with normal hearing (n = 10), Menière's disease (n = 10), presbycusis with flat audiograms (n = 4), and presbycusis with sloping audiograms (n = 5) were examined by light microscopy. Outer sulcus cells were assessed quantitatively and qualitatively in each cochlear turn. One specimen was stained for tubulin immunofluorescence and imaged using confocal microscopy. Outer sulcus cells interface with endolymph throughout the cochlea, with greatest contact in the apical turn. Mean outer sulcus cell counts in the upper apical turn (8.82) were generally smaller (all p < 0.05) than those of the upper basal (17.71), lower middle (18.99) upper middle (18.23), and lower apical (16.42) turns. Mean outer sulcus cell counts were higher (p < 0.05) in normal controls (20.1) than in diseased specimens (15.29). There was a significant correlation between mean cell counts and tonotopically expected hearing thresholds in the upper basal (r = -0.662, p = 0.0001), lower middle (r = -0.565, p = 0.0017), and upper middle (r = -0.507, p = 0.0136) regions. Other differences in cell morphology, distribution, or relationship with Claudius cells were not appreciated between normal and diseased specimens. Menière's specimens had no apparent unique features in the cochlear apex. Immunofluorescence staining demonstrated outer sulcus cells extending into the spiral ligament in bundles forming tapering processes which differed between the cochlear turns in morphology. Outer sulcus cells vary throughout the cochlear turns and correlate with hearing status, but not in a manner specific to the underlying diagnoses of Menière's disease or presbycusis.