If pituitary tumors become large, they can cause damage to the pituitary, resulting in hormone deficiencies (hypopituitarism) and/or damage to the surrounding structures. This can include visual loss, which is often characterized by loss of peripheral vision. It can also include headaches. Pituitary tumors that are functioning, i.e. that are secreting excessive pituitary hormones, can cause syndromes with specific symptoms depending on the hormone secreted. These include acromegaly, Cushing's disease, hyperprolactinemia and hyperthyroidism.

The cause of pituitary tumors is unclear. Most pituitary tumors arise spontaneously and are not genetically inherited. Many pituitary tumors arise from a genetic alteration in a single pituitary cell that divides repeatedly to form a tumor, which is almost always benign. This genetic change, or mutation, is not present at birth, but is acquired during life.

When pituitary tumors become large, they can cause pituitary hormone deficiencies (hypopituitarism), as well as damage to surrounding structures. This can result in visual loss, which is usually characterized by loss of peripheral vision. These complications can often, but not always, be reversed with treatment of the pituitary tumor, especially by surgery. Other complications of pituitary tumors depend on the hormone secreted.

Pituitary tumors are usually diagnosed by an MRI in conjunction with endocrine testing. The testing will determine whether the tumor is functioning (causing hormone excess) or nonfunctional and whether hormone replacement is required.

Treatment depends on the type and size of the tumor. Prolactinomas are usually treated with medication, whereas nonfunctiong tumors, GH-secreting tumors (acromegaly), ACTH-secreting tumors (Cushing's disease) and TSH-secreting tumors (thyrotrope adenomas) usually require transsphenoidal surgery. Medications and radiation are also available as a secondary treatment for many of these disorders.