The pituitary gland is a pea-sized structure that is attached to the undersurface of the brain by a thin stalk. It is protected by a cradle of bone called the sella turcica, which is located above the nasal passages, almost directly behind the eyes. The pituitary gland sometimes is called the master gland because it produces hormones that regulate many bodily functions, including the production of:
Sex hormones, such as estrogen and testosterone
Anti-diuretic hormone that helps control water balance
When tumors develop in the pituitary gland, they are usually small, localized, slow-growing masses that start in one type of hormone-producing pituitary cells. Although these tumors almost always are benign (noncancerous), they have the potential to cause significant symptoms by:
Producing too much of one of the pituitary hormones
Suppressing the normal function of other cells in the pituitary gland
Growing large enough to press on the nearby optic nerves (nerves that carry vision impulses from the eyes to the brain) or on parts of the brain itself
A pituitary tumor is classified as one of four main types, based on whether it overproduces pituitary hormones and the specific type of hormone produced:
ACTH-producing tumor — This pituitary tumor, which also is called a basophilic adrenocorticotrophic hormone-secreting adenoma, overproduces adrenocorticotrophic hormone (ACTH). ACTH is the pituitary hormone that regulates hormone production by the adrenal gland. When this type of pituitary tumor relaes too much ACTH into the bloodstream, the extra ACTH overstimulates the adrenal glands to pour out high levels of adrenal glucocorticoids (adrenal hormones) and androgens (male hormones) into the blood. In most cases, an ACTH-producing tumor is small and doesn't grow beyond the sella turcica.
Prolactin-producing tumor — This pituitary tumor, which also is called a prolactin-secreting adenoma, overproduces the hormone prolactin, which stimulates the breasts to make milk. Prolactin-producing pituitary tumors can develop in both men and women, and they sometimes grow so big that they press on the sella turcica and cause it to get larger.
Growth hormone-producing tumor — This tumor, which also is called an eosinophilic growth hormone-secreting adenoma, secretes abnormally large amounts of growth hormone. In children and teenagers, this overproduction of growth hormone causes a condition called giantism (excessive growth, especially in height). In adults, it causes a condition called acromegaly (abnormal enlargement of the skull, jaw, hands and feet, and other symptoms of abnormal growth). Growth hormone-producing tumors can grow beyond the sella turcica.
Non-functioning pituitary tumor — This type of pituitary tumor, which also is called a hormonally inactive adenoma, does not cause pituitary hormones and is slow to produce symptoms. For this reason, this type of tumor tends to grow large before it is discovered. In many cases, a nonfunctioning pituitary adenoma is diagnosed only when it already has grown beyond the sella turcica and has begun to cause problems related to pressure on the optic nerves or brain.
In the United States, pituitary tumors are diagnosed in 1 to 15 of every 200,000 people each year, most commonly in women between the ages of 15 and 44. However, autopsy studies suggest that a much larger percentage of the population — perhaps as high as 11% — may have very tiny pituitary tumors that never cause symptoms.