In some cases, enlargement of the pituitary is due to hyperplasia (increase in the number of cells), which may be a response to low levels of hormones from other glands (for example, low levels of thyroid hormone from the thyroid gland cause the pituitary to enlarge in order to produce more thyroid stimulating hormone ). The pituitary also normally enlarges during pregnancy due to hyperplasia. These causes of enlargement rarely cause symptoms.
In other cases, an enlarged pituitary gland may cause symptoms such as headaches. Because the growing gland often presses on the optic nerve, which passes above the pituitary gland, loss of vision may occur. Vision loss often initially affects only the upper, outermost fields of vision in both eyes.
Underproduction or overproduction of pituitary hormones may also occur.
Treatment depends on the cause of the enlargement. For example, if enlargement is due to a tumor, the tumor may be treated with surgery, radiation therapy, or drugs, depending on the type of tumor, its size, and the symptoms it causes.
(See also Overview of the Pituitary Gland.)