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The pituitary is a pea-sized gland located at the base of the brain. It is sometimes called the “master” gland because it controls and coordinates the release of hormones responsible for many of the body’s functions. However, it is controlled by higher centers in the brain.
The front part of the gland, known as the anterior pituitary, secretes several hormones, including:
The back part of the gland, or the posterior pituitary, secretes two hormones:
Pituitary tumors are almost always noncancerous, or benign. Benign tumors are called adenomas. Adenomas range in size from a few millimeters to several centimeters. Those with a diameter of less than 1 centimeter (the size of a dime) are called microadenomas, while those greater than 1 centimeter are called macroadenomas.
Doctors at NYU Langone identify and manage the two main types of benign tumors: nonfunctional and functional. They also manage the rare cancerous, or malignant, ones.
At least half of pituitary adenomas are nonfunctional, meaning they do not cause levels of pituitary hormones in your body to rise. However, nonfunctional tumors can grow large enough to cause symptoms, such as headache or vision problems, as they press on the nerves that lead from the eyes to the brain. Sometimes they press on the pituitary gland, causing pituitary hormone levels to drop.
Functional pituitary tumors produce high levels of one of the hormones listed above, leading to certain hormonal conditions. They can grow large enough to produce other symptoms, including headache and vision problems. Some functional tumors grow so large that they compress pituitary gland tissue, decreasing the secretion of other pituitary hormones.
The rare pituitary tumors that are cancerous, or malignant, can be functional or nonfunctional. Malignant tumors, also called pituitary carcinomas, can destroy pituitary tissue, causing a drop in hormone levels. Left untreated, pituitary cancer can affect vision, cause headaches, and eventually spread to the brain or the rest of the body.
Hyperprolactinemia is a condition that develops when pituitary tumors produce excess amounts of prolactin. These tumors are a type of functional adenoma called prolactinoma. When women have a prolactinoma, their menstrual periods may become irregular or stop, interfering with fertility. In some women, ovulation might cease, even though they are still experiencing a menstrual period. Women may also produce breast milk even though they have not recently given birth.
The role of prolactin in men is less understood. However, men can develop prolactinomas that cause hypogonadism, or low testosterone, leading to symptoms such as fatigue, erectile dysfunction, and decreased libido or sex drive. These symptoms develop gradually and may go unnoticed. If a person doesn’t notice the symptoms, prolactinomas can grow large enough to interfere with vision or cause headaches.
Doctors don’t know what causes these tumors, most of which develop spontaneously. Occasionally, a history of radiation therapy to the face or neck may be the cause. Prolactinomas are one of the few pituitary tumors that can usually be managed with medication alone. Therefore, knowing whether a pituitary tumor is a prolactinoma is very important before discussing whether surgery is necessary.
In Cushing’s disease, a pituitary adenoma produces too much adrenocorticotropic hormone (also called ACTH), which signals the adrenal gland to make excessive amounts of cortisol. Although rare, Cushing’s disease may develop when there is an overgrowth of normal cells that produce ACTH, which increases the adrenal gland’s cortisol production.
Symptoms include high blood pressure, high blood sugar (type 2 diabetes), weight gain, loss of muscle mass, and fragile bones (osteoporosis). People who have this condition often develop fat deposits on the face, upper back, shoulders, and midsection, as well as purple stretch marks on the thighs and abdomen, called striae, which do not go away. They also tend to bruise easily.
Functional pituitary tumors can produce excess growth hormone in adults, causing a condition called acromegaly. This causes the bones and soft tissues to grow, resulting in puffy or enlarged hands and feet; a widening of the jaw, forehead, and nose; and large spaces between the teeth. High levels of growth hormone can also cause high blood pressure, heart disease, type 2 diabetes, increased sweating, skin tags, and noncancerous growths in the colon called polyps.
Some tumors—both functional and nonfunctional—can grow large enough to compress the pituitary gland, resulting in a condition called hypopituitarism, in which the levels of one or more hormones decline. Symptoms depend on which hormone or hormones are affected.
Decreased levels of adrenocorticotropic hormone, or ACTH, for instance, can cause the adrenal glands to stop working properly. People with this condition, known as secondary adrenal insufficiency, may have low blood pressure, low blood sugar, fatigue, and a low tolerance for stress because of low cortisol levels.
If levels of follicle-stimulating hormone, also called FSH, and luteinizing hormone, called LH, decline, a person may have lower levels of the sex hormones estrogen and testosterone. This causes irregular menstrual periods, infertility, and a decreased sex drive in women. Men may also experience problems with infertility and sex drive. A deficiency in thyroid-stimulating hormone, called TSH, can result in lower levels of thyroid hormone, a condition called central or secondary hypothyroidism.
Low levels of growth hormones in adults can cause fatigue, increased body fat, and greater sensitivity to heat and cold.
Decreased levels of antidiuretic hormone can cause diabetes insipidus. In diabetes insipidus, the body cannot concentrate urine properly, so the urine is very dilute, resembling water. This causes frequent urination with dehydration and excessive thirst, especially for cold water.
This is different from diabetes mellitus, in which the urine contains a lot of sugar. Diabetes insipidus is rarely seen with pituitary adenomas, but it may be seen with trauma to the pituitary and other diseases, such as sarcoidosis, that affect the gland.
Rarely, functional pituitary tumors produce too much thyroid-stimulating hormone, or TSH, causing the thyroid gland to produce excess levels of thyroxine, a hormone that regulates the body’s metabolism. This results in a condition called secondary hyperthyroidism, which can lead to high blood pressure, an irregular heartbeat, an increased appetite, and weight loss. These tumors are extremely rare and are the least likely cause of hyperthyroidism.
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