Located in the brain, the pituitary gland is often referred to as the "master gland" of the body. This is because it makes and releases (secretes) at least nine distinct hormones (including oxytocin, antidiuretic hormone [ADH], prolactin, thyroid-stimulating hormone [TSH], adrenocorticotropic hormone [ACTH], follicle-stimulating hormone [FSH], luteinizing hormone [LH], and human growth hormone [HGH]) that regulate the activities of several other endocrine glands and influence a number of physiological processes including growth, sexual development and functioning, and the fluid balance of the body. The pituitary is divided into two parts: front (anterior) and rear (posterior). Each half of the pituitary gland secretes specific hormones. Tumors in the anterior part are common and are usually noncancerous (benign). Tumors rarely develop in the posterior portion. Between 10% and 15% of all tumors in the skull are pituitary tumors, which makes them the third most common type of brain tumor.
Virtually all pituitary tumors arise from a single cell which, for unknown reasons, has grown out of control. Tumors that have originated from a single cell are called monoclonal. Some tumors secrete hormones normally made by the pituitary gland. Because the tumor cells are uncontrolled, they secrete large amounts of hormones. As a result, hormone imbalance occurs. The symptoms caused by the hormone imbalance are often the first sign of a pituitary tumor.
There are several different types of pituitary tumors. Pituitary adenomas (adenomas are tumors that grow from gland tissues) are the most common type. Most pituitary adenomas are benign, although they may spread to nearby tissues. Pituitary adenomas can be further classified based on which, if any, hormones are secreted by the tumor. Thirty-five percent of pituitary adenomas do not secrete hormones, 27% secrete prolactin (prolactinomas), and 21% secrete growth hormone. The remaining pituitary adenomas secrete sex hormones (6%), thyroid hormones (1%), or adrenal (adrenocorticotropic) hormones (8%). Plurihormonal adenomas secrete more than one type of hormone. Tumors that secrete adrenocorticotropic hormone cause Cushing's syndrome and Nelson's syndrome.
Craniopharyngiomas are benign tumors that originate in tissues next to the pituitary gland. Technically speaking, they are not pituitary tumors although they affect the pituitary gland. They are extremely difficult to remove and radiation does not stop craniopharyngiomas from spreading throughout the pituitary gland. Craniopharyngiomas account for less than 5% of all brain tumors.
Pituitary carcinoma is a very rare condition. Fewer than 100 cases have ever been reported. It is usually
diagnosed when a pituitary tumor, which was believed to be an adenoma, spreads (metastasizes) to distant organs. These pituitary tumors may or may not release hormones. Because pituitary carcinoma is often diagnosed late, it has a high death rate.
Maureen Haggerty, Belinda Rowland Ph.D., The Gale Group Inc., Gale, Detroit,