Cysts in the rat adenohypophysis: incidence and histology

The incidence and histology of cysts in the adenohypophysis of adult male Wistar rats are reported. Of sixty pituitaries studied 13 of them (21.6%) presented a single cyst located in the pars distalis. The cysts varied in shape and size and were usually multilocular. Two of them were connected with the subdural space at the ventral surface of the adenohypophysis. Histology demonstrated that the cysts were filled with mucinous material and foamy macrophages and were lined by flat and cuboidal ciliated and nonciliated epithelial cells, goblet cells as well as several adenohypophysial endocrine cells such as somatotrophs, thyrotrophs, and gonadotrophs. The ciliated cells were the most numerous. Histologic and immunohistochemical studies of the uninvolved areas of the adenohypophysis showed no abnormalities and the weights and histology of the adenohypophyses and peripheral endocrine glands were within normal range, suggesting that the cysts did not impair the adenohypophysial endocrine activity. Although the morphogenesis of the cysts remained obscure, the histological and immunohistochemical findings support the hypothesis that during embryonic development, the future cysts coming from the pharyngeal epithelium is fused with the stomodeum before or during the formation of the Rathke's pouch.