Enlargement of the gland can cause local symptoms such as headaches or visual disturbances. Autopsy studies indicate that 25 percent of the U.S. population have small pituitary tumors. Forty percent of these pituitary tumors produce prolactin, but most are not considered clinically significant. Clinically significant pituitary tumors affect the health of approximately 14 out of 100,000 people. Although research continues to unravel the mysteries of disordered cell growth, the cause of pituitary tumors remains unknown.
Most pituitary tumors are sporadic.
They are not genetically passed from parents to offspring. In women, high blood levels of prolactin often cause infertility and changes in menstruation. In some women, periods may disappear altogether. In others, periods may become irregular or menstrual flow may change. Women who are not pregnant or nursing may begin producing breast milk.