Explanation and implications of MR signal changes within pituitary adenomas after bromocriptine therapy.

The pituitary gland has only recently been studied with magnetic resonance (MR) imaging. Initial results suggest MR may have utility in the detection and follow-up of pituitary microadenomas [1]. Of interest, it has been observed that prolactinomas treated with bromocriptine may manifest distinct and diverse MR signal changes [1] . Bromocriptine, a dopamine agonist, has been effective in the symptomatic treatment of many prolactinand in rare instances growth-hormone-secreting tumors, causing reduction in tumor size and normalization of elevated serum hormonal levels. The apparent MR signal changes that have been observed thus far using spin-echo pulse sequencing are increased signal intensity on T1-weighted sequences suggesting shortening of T1 relaxation time and both increased or decreased signal intensity on T2-weighted sequences suggesting, respectively, prolongation or shortening of T2 relaxation time. Initial surveys suggest that about onethird of prolactinomas clinically responsive to bromocriptine manifest MR signal changes (Bradley WG Jr, personal communication). I wish to propose an explanation of this phenomenon that considers histologic changes observed in prolactinomas responsive to bromocriptine therapy. I also wish to speculate on possible implications these MR signal changes may have in the initial diagnosis and management of prolactinand possibly growth-hormone-secreting pituitary adenomas. Several histologic changes are observed in prolactinomas after short-term (6 weeks) bromocriptine administration [2 , 31: (1) marked reduction in tumor cell size , primarily because