Pituitary tumors in MEN1: do not be misled by borderline elevated prolactin levels.

Small, intrasellar microadenomas may be associated with elevated PRL levels due to possible direct hormone production [prolactinoma] or possibly to interference with portal vessel blood flow. In monitoring hyperprolactinemic MEN1 patients for the development of pituitary adenomas, measurement of PRL levels is insufficient and periodic MRI scans are necessary at a more frequent interval than every 3-5 years. This may also pertain to patients with "idiopathic" hyperprolactinemia.