A pituitary tumor is an abnormal growth of cells in the pituitary gland. This gland is located within the base of the skull, at the center of the brain, and is the main hormone producing gland in the body. Hormones are chemical substances the body produces that control and regulate certain cells or organs. A tumor in the pituitary gland can cause the cells in the gland to overproduce certain types of hormones which can cause a patient to get sick. They could also compromise the function of the hormone producing cells leading to a deficiency of particular hormones.
About 10% of all primary brain tumors are pituitary tumors. The overwhelming majority of pituitary tumors are benign in nature. Pituitary tumors are classified based upon their size and whether they secrete a particular hormone. Tumors greater than 10mm are referred to as macroadenomas, and tumors less than 10 mm are classified as microadenomas. Pituitary tumors that secrete hormones are called secretory tumors and those that do not secrete any hormones are termed non-secretory or non-functioning pituitary tumors. As a result of the location of the pituitary gland, at the base of the skull, pituitary tumors usually grows upwards. Eventually, some of these tumors enlarge enough that they cause compression of the nerves to the eyes (optic nerves), resulting in visual loss or loss of peripheral vision. The pressure of the tumor on the surrounding structures can also cause headaches, which are typically located behind the eyes. Patients with secretory pituitary tumors can also manifest with syndromes associated with an excess of the particular hormones. Some patients could also present with symptoms of hormone deficiency.
There is no obvious cause of pituitary tumors. Some pituitary tumors might be caused by stimulation from the hypothalamus — a part of the brain that signals the pituitary gland to make hormones. People who have the rare inherited conditions such as multiple endocrine neoplasia type 1 (MEN-1) — a disorder that causes tumors in the endocrine glands (which secrete hormones into the bloodstream and include the pituitary gland) and the first part of the small intestine — or Carney complex — a disorder that causes several types of tumors, including in the pituitary gland — have a higher risk of pituitary tumors. About 1-5% of pituitary tumors occur within families.