A double pituitary adenoma presenting as a prolactin-secreting tumor with partial response to medical therapy. Case report.

Double pituitary adenomas are difficult to recognize pre-operatively as only a single mass may be appreciated on imaging. We present herein a giant prolactin-secreting pituitary adenoma in a middle-aged man that had responded partially to dopamine agonist therapy. The excised specimen demonstrated a double adenoma. The prolactin-producing one displayed the expected morphological changes resulting from medical therapy, while the other, a gonadotroph adenoma, did not. The failure of tumor shrinkage can be attributed to the presence of a double adenoma, a previously unreported cause of failure of medical therapy in prolactinoma.