Electron microscopic studies of human pituitary tumors. II. Acidophilic adenomas

Nine cases of acidophilic adenoma associated with acromegaly were studied by electron microscopy. The tumor parenchyma contained numerous cells identifiable as somatotrophs, many of which appeared “normalt” and apparently engaged in protein synthesis. In about half of the specimens, there were variations in the electron-opaque characteristics of the parenchymal cells, most frequently affecting somatotrophs. Characteristic of some somatotrophs was a marked electron-opacity of the cytoplasmic matrix and nuclear materials, irregular cell contours, hypertrophied cytomembrane systems frequently containing proteinaceous material, and considerable amounts of secretory granules. Disruptions in plasma membranes were apparent throughout the parenchyma, particularly at the parenchymal-pericapillary interface. This resulted in the release of large numbers of secretory granules and cytoplasmic fragments to pericapillary or extracellular spaces. Small groupings of the disrupted cells often were characterized by scant secretory granules, an electron-lucent cytoplasmic matrix, and were considered the counterpart of giant multinucleate chromophobes observed with the light microscope. Follicular cells were observed rarely, but when present contained an abundance of fine cytoplasmic filaments and closely resembled follicular cells described in ACTH-secreting tumors.