pituitary adenoma

A pituitary adenoma is a (usually benign) overgrowth of cells in the pituitary gland. Think of it as a small lump that arises from one of the pituitary's hormone-making cell types. It is very common and frequently causes no trouble at all.

Adenomas cause problems in two broad ways. Some are “functional,” meaning they oversecrete a hormone: a prolactinoma floods the body with prolactin, a growth-hormone tumor causes acromegaly, and an ACTH-secreting tumor causes Cushing's disease. Others are “non-functional” and make trouble only by their size.

Because the pituitary sits in a tight bony space below the brain, a growing tumor can press on neighboring structures. Pushing upward on the optic chiasm classically causes loss of the outer visual fields, and squeezing the rest of the gland can lead to hypopituitarism — deficiency of one or more normal pituitary hormones.

Adenomas are often divided by size into microadenomas (under 10 millimeters) and macroadenomas. Treatment depends on the type: prolactinomas usually respond to dopamine-agonist drugs, while many other adenomas are managed with surgery, medication, or radiation as needed.