Definition of Pituitary tumor:

A pituitary tumor is an abnormal growth in the pituitary gland, the part of the brain that regulates the body's balance of hormones.

Causes, incidence, and risk factors:

The pituitary gland is a pea-sized endocrine gland located at the base of the brain. The pituitary regulates and controls the release of hormones from other endocrine glands, which in turn regulate many body processes. These hormones include:

• Adrenocorticotropic hormone (ACTH)
• Growth hormone (GH)
• Prolactin
• Thyroid-stimulating hormone (TSH)

About 75% of pituitary tumors release hormones. When a tumor produces too much of one or more hormones, the following conditions may occur:

• Central hypothyroidism (excess thyroid-stimulating hormone)
• Cushing syndrome (excess adrenocorticotropic hormone)
• Gigantism or acromegaly (excess growth hormone)
• Prolactinoma (excess prolactin)

As the tumor grows, hormone-secreting cells of the pituitary may be damaged, causing hypopituitarism.

The causes of pituitary tumors are unknown, although some are a part of a hereditary disorder called multiple endocrine neoplasia I (MEN I).

There are other types of tumors that can be found in the same area of the head as a pituitary tumor:

• Craniopharyngiomas
• Cysts
• Germinomas
• Tumors that have spread from cancer in another part of the body (metastatic tumors)

About 15% of tumors in the skull are pituitary tumors. Most pituitary tumors are located in the anterior pituitary lobe and are usually noncancerous (benign).

Pituitary tumors develop in about 20% of people, although many of the tumors do not cause symptoms and the condition is never diagnosed during the person's lifetime.