Morphometric analysis of fibers of the human vestibular nerve: sex differences.

The aim of this study was to analyze myelinated axons in the human vestibular nerve (VN). We assumed that a smaller total number and average transverse area of myelinated axons in the female than male VN, would partly explain the female preponderance of vestibular disorders. The materials were obtained from 24 cadavers (12 females and 12 males) aged 54-90 years (average 74.8 years). We counted the myelinated axons, measured the transverse area of the myelinated axons, and analyzed morphological differences between the female and male specimens. The total number differed significantly between the female and male specimens. The older generation of both sexes tended to have lower total counts, but there was no significant difference among the generations. The average transverse area of the myelinated axons did not differ significantly between the female and male specimens. The older generation of both sexes tended to have a smaller average transverse area, and there was a significant difference among the generations. The presented results indicated that the lower total number, not the average transverse area, of myelinated axons in the female VN might be one of the reasons why vestibular disorders have a female preponderance.