Ultrastructure of parathyroid adenomas.

The ultrastructure of 12 cases of parathyroid adenomas is analyzed in the light of recent discoveries of biochemical functions of the parathyroids. Variants of parathyroid chief cells forming the adenomas are illustrated and cytologic details are explored. The correlation of cytoplasmic structures with hormone synthesis, transfer, secretion and intracellular lysosomal degradation is reviewed. A hormone secretory cycle in parathyroid adenomas is not observed. Current knowledge of parathyroid biochemistry does support modulation of hormone production and degradation by parathyroid chief cells rather than a cyclic secretory activity. Unusual structures and alterations of the normal organelles found in parathyroid adenomas are described and illustrated. Contrary to detailed knowledge of hormone synthesis, little is known about other metabolic and structural alterations in these adenomas. The reasons for massive accumulation of lipid, glycogen and mitochondria remain to be explored. As yet, neither ultrastructural investigation nor better understanding of biochemical processes of hormone production have led to recognition of etiologic factors inducing parathyroid adenomas.