What are Pituitary Tumors?

Pituitary tumors are tumors that start in the pituitary gland, which is a small pea-sized gland at the base of the brain. The pituitary gland makes hormones that control many bodily functions, including the levels of hormones produced by other glands in the body. Pituitary tumors, also known as pituitary adenomas (recently referred to as pituitary neuroendocrine tumors), are almost always benign; however, these tumors can still cause serious medical problems. Pituitary tumors may grow large and inhibit the normal function of the pituitary gland or press on nearby structures such as the optic nerve, resulting in loss of vision. Pituitary tumors may also produce excessive amounts of certain hormones that regulate multiple bodily functions. This may cause specific medical problems and physical changes. Pituitary tumors are often divided into two categories: functioning and non-functioning.

Functioning Pituitary Tumors

Functioning pituitary tumors overproduce certain hormones. In functioning tumors, these high levels of hormones are responsible for the symptoms of the disease. The hormones that pituitary tumors can affect may include:

• Prolactin: Prolactin is the hormone needed to produce breast milk in women. Pituitary tumors that cause the overproduction of prolactin are called prolactinomas and are the most common pituitary tumors. Pituitary tumors that cause the overproduction of prolactin can result in a condition known as galactorrhea (milk secretion from breasts) or can impair sexual function (hypogonadism).
• Growth Hormone (GH): Growth hormone is a hormone that helps control growth of body parts and energy metabolism. Pituitary tumors that cause the overproduction of growth hormone result in a condition known as acromegaly. These tumors are the second most common functioning pituitary tumors.
• Adrenocorticotropic Hormone (ACTH): ACTH is a hormone that controls the production of cortisol by the adrenal glands. Cortisol is commonly referred to as the "stress hormone" because it is usually produced in response to stress. Pituitary tumors that produce too much ACTH cause Cushing disease.
• Thyroid-stimulating Hormone (TSH): TSH controls the production of hormones by the thyroid gland. Elevated levels of TSH may cause the overproduction of hormones by the thyroid gland, and may lead to hyperthyroidism. Pituitary tumors that produce too much TSH are very rare.
• Gonadotropins: The gonadotropins are luteinizing hormone (LH) and follicle stiumlating hormone (FSH). These hormones control ovarian function in women and testicular function in men. Pituitary tumors that produce too much of these hormones are often clinically silent and often get classified clinically under nonfunctioning tumors.

Non-functioning Pituitary Tumors

The clinical features of growth hormone excess (acromegaly) or cortisol excess (Cushing syndrome) are not seen in non-functioning pituitary tumors. However, these tumors may interfere with normal hormone production by the pituitary or grow large and press into nearby structures, such as the optic nerve, causing symptoms such as visual impairment. These tumors are the second most common type of pituitary tumor after prolactinomas.

Pituitary carcinomas

Malignant pituitary tumors are very rare, but may occur in some instances. Most pituitary carcinomas produce excess amounts of prolactin or ACTH. These tumors may also invade nearby structures and spread to the central nervous system or other parts of the body.