Ultrastructural-morphometric effects of radiotherapy on pituitary adenomas in acromegaly.

Within a series of 22 irradiated GH-producing adenomas we studied by light microscopical and morphometrical means the grading of nuclear pleomorphism, the proportion of densely granulated cells, the number of mitoses, multinuclear cells, necrotic or necrobiotic cells, and the degree of fibrosis in comparison to non-irradiated tumours. By electronmicroscopical morphometry we investigated the changes in area, circumference, area percentage, and number of intracellular structures. The rate of necrobiotic cells and the grade of nuclear pleomorphism were significantly higher in the irradiated tumours. The fibrotic areas were larger. No differences were observed in the degree of granulation and the rate of multinuclear cells. Mitoses were found in only one tumour. Within the group of the well-differentiated adenomas the areas and circumferences of the nuclei, nucleoli, mitochondria, immature secretory granules, and secretory granules increased significantly. The area percentages of the nuclei, mitochondria, immature secretory granules, and secretory granules increased as well. The mitochondria, Golgi-fields, and the rough endoplasmatic reticulum decreased in number. The undifferentiated adenomas changed almost in the same significant way. To us most of these changes are a sign of irradiation damage. The enlargement of intracellular structures could be a sign of an increased rate of secretory activity.