Fine structure of human pituitary adenoma

Biopsy specimens from 6 cases of chromophobe adenoma were studied by electron microscopy. The basic histological pattern of the tumor was distinctly reminiscent of the normal pituitary. Most of the findings were in agreement with those of other workers, but several new, alternative interpretations regarding the fate of the secretory granules and the nature of some variations in cellular morphologic findings are discussed. The following observations are worth mentioning. Secretory granules were observed in the perivascular spaces, but these were usually accompanied by other cell debris, which were clearly the results of cell lysis. The secretory granules within the perivascular spaces usually retained their limiting membranes, thus leading support to the idea that their presence there was the result of cell death and not as a part of the secretory process. In addition to the more common type of tumor cells, which usually contain moderate numbers of secretory granules, other cells with substantially fewer granules were also observed. Most authors compared these to the structures in normal, mature pituitary and concluded that they represent secretory cells that have already discharged their secretory products. However, the present authors do not see how one can rule out the possibility that, in fact, these cells are young, neoplastic cells, which have not yet differentiated sufficiently to form secretory granules. An apparently new finding is the presence of asymmetric crescent shaped membranous densities. Superficially, these structures are reminiscent of synapses, but no secretory vesicles were found associated with them. Intercleft densities are absent and it is not even clear that the enclosed cytoplasmic areas are actually cell processes.