Temporal bone histopathology in experimental hypovitaminosis A.

Twenty-five years ago hearing loss was observed in some subjects during a comprehensive study of the effects of hypovitaminosis A on human volunteers. Experimental studies documenting histopathological changes in the temporal bone due to hypovitaminosis A are conflicting. Even the recent textbooks of otolaryngology and physiology make no mention of a role of vitamin A in the ear. To explore the role of vitamin A in the ear adult and weanling rats maintained on a diet totally lacking vitamin A were sacrificed at intervals. Their temporal bones were examined with the light microscope. After six weeks on a vitamin A free diet weanling rats showed hypertrophy of the periostial portions of the otic capsule. At 16 weeks a narrowing of the internal auditory canal due to bony exostoses was present. The neuroepithelia of the cochlea and the vestibular apparatus were histologically normal even in the longest surfiving animals. Adult rats maintained on a vitamin A free diet showed minimal thickening of the bone adjacent to the internal auditory meatus. The cochlea and the vestibular appartus in these animals remained normal throughout the 28-week experiment. Although we have demonstrated marked abnormalities of the otic capsule in hypovitaminosis A, our results do not support those of some earlier investigators who reported that atrophy of the cochlear and vestibular neuroepithelium occurred in the absence of dietary vitamin A.