Perivascular fibrosis in prolactinomas: is it increased by bromocriptine?

Prolonged treatment of patients with pituitary prolactinomas with bromocriptine may increase the consistency of the tumor thereby making selective extirpation more difficult. We made quantitative determinations of the amount of perivascular fibrous tissue in prolactinomas on random electron micrographs, comparing a group of 21 patients treated with bromocriptine for periods longer than 3 months and a control group of 21 patients who did not receive bromocriptine. Statistical analysis of the data showed a significant increase of perivascular fibrous tissue in the treated group (P less than 0.002). We suspect that this fibrosis is a consequence of the rapid shrinkage of prolactinoma cells caused by bromocriptine. Presumably, this cell shrinkage causes enlargement of the extracellular and perivascular spaces which are filled by the deposition of collagen, producing a more dense consistency of the adenoma.