Pituitary adenomas producing growth hormone in acromegalic patients.

Growth hormone was shown in histological sections of 25 pituitary adenomas from acromegalic patients by means of the unlabelled peroxidase-antiperoxidase (PAP) technique. On the basis of the numbers of cytoplasmic granules, the cells of the adenomas were of two types: densely granulated and sparsely granulated. The densely granulated cells had abundant cytoplasm containing numerous granules, whereas the sparsely granulated cells had little cytoplasm with scanty granules. Depending on the predominant cell type the adenomas were also classified as densely granulated or sparsely granulated: 21 of the 25 adenomas (84%) were densely granulated and four (16%) sparsely granulated. There was some variation, however, in the relative numbers of the two types of cell from one part of an adenoma to another, a feature consistent with one type of cell in different phases of activity. There was no significant difference in mean serum growth hormone concentrations between the two groups, and granularity of the adenomas in histological sections did not therefore correlate with secretory activity. Nine adenomas showed extrasellar extension. The mean serum growth hormone concentration in these cases was lower than the mean of the adenomas confined to the sella turcica. Thus the size of the tumour did not correlate with the serum growth hormone concentration. Three of the four adenomas in the sparsely granulated group showed extrasellar extension, compared with 6 of 21 classified as densely granulated. This suggests that sparsely granulated adenomas have a more aggressive pattern of behaviour, but histological evidence for this was lacking.