Pituitary adenomas are benign tumors which arise from the pituitary gland itself. They are almost never malignant. Pituitary tumors can be either secretory or non-secretory, referring to whether they overproduce pituitary hormones. Secretory tumors cause disease because of the excess quantities of hormones which they secrete (release) into the bloodstream. The most common type of secretory pituitary tumor is termed a prolactinoma. Excess prolactin in the blood may lead to irregular or absent periods in women, decreased libido and erections in men and infertility or milk production in men or women. However, there are excellent medicines available to treat this disorder, so surgery is rarely needed. Most patients with prolactinomas are treated by endocrinologists, who are medical specialists in gland and hormone disorders.
Secretory tumors, which commonly require surgery, include those which cause acromegaly and Cushing's disease. Acromegaly (or gigantism if occurring in a child) results from an excess of growth hormone production. Too much adrenocorticotropic hormone (ACTH) leads to overproduction of cortisol by the adrenal glands, giving rise to a disorder called Cushing's disease. Surgical removal of these tumors can restore normal hormone production in many cases. Non-secretory tumors (which are also termed non-functioning) do not overproduce hormones, but cause problems due to their size and location. This is because they can compress both the normal pituitary gland and the surrounding structures. Hormone deficiencies may result from compression of the normal pituitary gland. Non-secreting tumors can also cause vision problems by growing upwards and compressing the optic nerves and chiasm, nerves which are important for vision. This pressure can lead to loss of peripheral vision. Surgery can remove such tumors and relieve the pressure on surrounding structures.