[Histogenesis of adenomas of the parathyroid gland]

The similarity of adenomas of the parathyroid gland with other tumours of the APUD-system elements was investigated. The structure of 10 adenomas was studied. The ultrastructural characteristics were compared with the histological structure of the tumour. Various histological variants of the neoplasias were shown to have similar ultrastructure. The tumour tissue was represented by clear transitional and dark cells. In their cytoplasm, osmiophilic granules of the secrete, villae, laminar structures resembling Nissl bodies, fine granular and fine fibrous substances, and lipid inclusions were found. The structural similarity of adenomas with other endocrine-active tumours developing from cells of the neuroectodermal origin (carcinoids, paragangliomas, etc.) was noted. It is suggested that parathyroid glands belong to the APUD-system.