The ultrastructure of human pituitary adenomas.

Ultrastructural examination of 28 human pituitary adenomas was performed. Findings were correlated to the clinical history and light microscopic observations. As revealed by light and electron microscopy 15 adenomas were of the chromophobe type causing no endocrine dysfunction. In 8 cases acidophilic adenomas were associated with endocrine symptoms. In this group two adenomas were of the densely granulated type, whereas 6 of the sparsely granulated type. The latter showed marked ultrastructural signs of enhanced secretory activity. Five cases corresponding electronmicroscopically to sparsely granulated acidophilic adenomas but causing no endocrine symptoms constituted a separate group. They suggest the possibility of the production of abnormal proteins by this type of adenoma cells. Oncocyte cell-groups were seen in chromophobe adenomas. Morphometric data on granule size and distribution proved to be useful in the differentiation of chromophobe and acidophilic adenomas. Hypertrophic cell organelles, filamentous and tubular structures are interpreted as ultrastructural signs of cellular adaptation.