Morphologic evidence for three cell types in the human spiral ganglion.

Although two types of spiral ganglion cells (large type I and smaller type II) have classically been described by anatomic studies in both animal and human spiral ganglion, there is physiologic and morphologic evidence for subtypes of the large type I ganglion cell. In addition, in the animal and human, a variety of morphologic differences based on cytoplasmic content, myelinization, immunostaining and morphometric analysis have suggested more than one variety of type I ganglion cell. Light and electron microscopic serial sections of the spiral ganglion in two human specimens in the basal, middle and upper middle turns were pooled for morphometric analysis of the cell area, nuclear area and axon diameter. Analysis of variance, bivariate scatter plots and multivariate cluster analysis provided evidence for 3 types of ganglion cells in the human spiral ganglion: large, intermediate and small, varying from each other significantly on the basis of cell area. It was suggested, based on the morphologic findings and prevalence of the cell types, that the large and intermediate cells were subtypes of the classic type I spiral ganglion cell, whereas the small ganglion cell was consistent with the classically described type II ganglion cell.