Ultrastructure of chromophobe adenoma of the human pituitary gland.

Sixteen specimens of pituitary adenoma were studied by electron microscopy. Twelve of them were "non-functioning" tumours and four were associated with acromegaly. All the tumours showed the light-microscopic appearance of classical chromophobe adenoma. Though electron microscopy revealed varying degrees of granularity in the majority of the cells in all the tumours, two distinct morphological types of chromophobe tumours were observed. In one type, secretory granules were frequently seen in moderate or large numbers and the cells were poor in RER and Golgi apparatus. These cells are considered to be secretorily inactive storage cells and they were the predominant cells in eight cases of "non-functioning" adenomas. The other type was noted in four cases of "non-functioning" adenomas and in all the four cases of adenoma with acromegaly. In this type, the tumour cells were generally poor in secretory granules but were rich in RER and Golgi apparatus, suggesting secretory activity. In acromegaly these features appear to indicate active hormone synthesis and its discharge into the circulation but the reason for the morphological evidence of active secretion in the four cases of "non-functioning" adenoma is not clearly understood.