Morphologic and Morphometric Study of Human Spiral Ganglion Development

Abstract

A light microscopic study of the spiral ganglion was done in human embryos and fetuses measuring 45, 50, 60, 74, 90, 134, 270 mm crown-rump length (crl), and in a one-day-old neonate. Morphometric evaluations of i) cell and nuclear area, ii) nuclear area/cell area ratio, iii) ganglion area, iv) cell concentration/surface unit, and v) distance between the first neuron and the receptor were made, and the results statistically evaluated. In earlier stages of development, spiral ganglion primordia appeared as a cluster of neuroblasts and some schwannoblasts immersed in the mesenchymal tissue, close to the ductus cochlearis. A honeycomb pattern in the spiral ganglion neurons was observed in the basal turn of a 74 mm crl fetus. In later stages, the basal turn of a 90 mm crl fetus showed a spatial organization. Peripherical and central fibers of the acoustic nerve appeared stratified in early periods of development (45 mm crl embryo). From this stage on, both phenomena progress apicalwards until the neonatal period. A significant decrease in the nuclear area/cell area ratio was observed from the 134 mm crl fetus (17 weeks) to the neonatal stage in all turns. This led to a significant increase in cellular area from the 270 mm crl fetus (32 weeks) to the neonate, with no significant variation in nuclear area. The distance from the primordium of the organ of Corti to the spiral ganglion in the interval between 45 and 74 mm crl showed a significant increase in all turns. This initial proximity to the cochlear duct suggests an otocystic origin. This finding, and the presence of schwannoblasts in the central projections of the auditory nerve from the 45 mm crl embryo to the neonatal stage, are also suggestive of neural crest induction. A significant reduction in the number of spiral ganglion neurons was observed in all turns throughout development, whereas spiral ganglion area increased. Only two neuronal populations were found in the neonate basal and middle turns. During the fetal period, only one population appeared.

Key Words:

• Human spiral ganglion
• morphometry
• development