A pituitary tumor is an abnormal growth of pituitary cells. Pituitary tumors can either be nonfunctional (that is they do not secrete hormones) or produce specific hormones, such as prolactin (causing infertility, decreased libido, and osteoporosis), growth hormone (causing acromegaly), ACTH (causing Cushing’s), TSH (causing hypothyroidism), or be nonfunctional (that is they do not produce hormones). These tumors behave according to their cell of origin and are named for the specific cell type affected. For example, if a tumor originates in a prolactin producing cell, the patient develops a prolactinoma-a prolactin secreting pituitary tumor that is common and usually treatable. High prolactin levels suppress production of the pituitary hormones (luteinizing hormone and follicle stimulating hormone) that stimulate production of estrogen or testosterone. Men with these tumors have low testosterone levels and lose their sex drive and eventually their masculine characteristics-hair, muscle, erections, and ability to produce sperm. Women with prolactin producing tumors often do not ovulate, experience low estrogen levels, and cease having menstrual periods. In both cases, patients with low sex hormones develop osteoporosis. It is important to remember that most pituitary tumors are benign and cancer is very rare. They have variable patterns of growth and affect different people in vastly different ways. Some are small and incidental, while others are small but cause hormone excess. Others may be rapidly growing mass lesions.
