Ultrastructure of the vestibular dark cell area in patients with acoustic neurinoma.

The human vestibular dark cell (DC) areas of the utricle and ampulla of the lateral semicircular canal were investigated ultrastructurally in 7 patients with acoustic neurinoma. Two types of DCs mainly constituted the epithelial cells of the DC area. One type of DC had basolateral infoldings that were closely interwoven with the melanocyte processes, and the pinocytotic vesicles were frequently found within the basolateral infoldings and the melanocyte processes. The other type of DC had basolateral infolsings stacked upon each other. The former type of DC was more frequently found than the latter type in the DC area adjacent to the sensory epithelium and in the mid portion of the DC area. However, the latter type of DC was more predominant in the DC area distant from the sensory epithelium. These findings suggest that the activity of DCs is modulated by the melanocytes and that the former type of DC has a more active role in ion and/or fluid transport than the latter type of DC. Thus, the DC area near the sensory epithelium might be more actively engaged in the production and regulation of vestibular endolymph than that distant from the sensory epithelium.