Postnatal maturation of human spiral ganglion cells: light and electron microscopic observations

The presence of two types of ganglion cells, based on cell size and other morphologic parameters, is well established in the adult mammalian and human spiral ganglion. On the other hand, there is little data concerning cell morphology in the neonatal spiral ganglion. The present study was undertaken to evaluate the differences in the morphometry and distribution of cell types in the spiral ganglion of the human neonate as compared to the adult. A total of five human temporal bones from two neonates and three infants were included in this study. Light microscopic analysis of all specimens was performed, and electron microscopic evaluation of a 14 day old neonatal spiral ganglion was accomplished. The segmental density of spiral ganglion cells was higher in the neonate than in the adult. The prevalence of type II spiral ganglion cells was higher in the neonate than has been reported in the adult, particularly in the middle and apical turns where type II cells constituted 24% and 26% of all ganglion cells, respectively. The prevalence of type II ganglion cells decreased with age, particularly in the middle and apical turns. In the neonate, the maximal cross sectional area of type I neurons increased from the base to the apex and seemed to increase with age especially in the basal turn. The present study strongly supports a clear differentiation of type I and type II ganglion cells in the human neonate and that the prevalence of type II cells is greater in the neonate than the adult. This finding is discussed with reference to postnatal development of the spiral ganglion.