A tumor, usually benign, of the pituitary gland, usually resulting in amenorrhea and anovulation. Often there is an increase (sometimes substantial) in serum prolactin. If the tumor is itself secreting prolactin it is called a prolactinoma. But other tumors can occur, some of which secrete other pituitary hormones. The tumor grows inside a confined space with walls of bone called the pituitary fossa: if it is still small and confined to the fossa we call the tumor a microadenoma; if it enlarges the fossa or pushes out of it, it is a macroadenoma, and is both more dangerous and capable of producing visual symptoms and headaches. Diagnosed on a CAT scan or a MRI scan. Prolactin-secreting microadenomas can usually be treated just with drugs.