Necroses of prolactin-secreting pituitary adenomas under treatment with dopamine agonists: light microscopical and morphometric studies.

In order to clarify the mechanism by which prolactin-secreting adenomas reduce in size during treatment with dopamine agonists (DA), we studied altogether 18 chromophobe pituitary adenomas by carrying out light microscopical cell counting of necrobiotic alterations and necroses in photographs of semi-thin sections. Depending on hormonal activity and preoperative treatment of the patients 3 groups of adenomas were formed: 6 prolactin producing adenomas were treated with bromocriptine and lisuride (group 3). 8 cases remained preoperatively without medical treatment (group 2). For comparison, we studied 4 cases of clinically inactive pituitary adenomas (group 1). All adenomas were immunohistologically positive for prolactin. By classifying each tumor cell in one of four stages of necrotic alteration (stage 1: intact cell, stage 2: slightly condensed nucleus and shrunken cytoplasm, stage 3: necrotic cell with still visible nuclear membrane, stage 4: cell debris) we arrived at an index for necrobiotic alterations of the 18 adenomas. We found a significantly higher rate of cell necroses in DA-treated tumors compared with preoperatively untreated prolactinomas and inactive adenomas. Previous investigations in this field have revealed that a reduction in cell size may well cause the shrinkage of the prolactinomas after DA-therapy. The results presented in this paper indicate, however, that the role of necroses now needs to be given much closer attention as an additional factor.