What are pituitary tumors?
To understand pituitary tumors, it helps to know about the normal structure and function of the pituitary gland.
The pituitary gland
The pituitary is a small gland found inside the skull just above the nasal passages, which are above the fleshy back part of the roof of the mouth (known as the soft palate). The pituitary sits in a tiny bony space called the sella turcica. The nerves that connect the eyes to the brain, called the optic nerves, pass close by it.
The pituitary gland is connected directly to part of the brain called the hypothalamus. This provides a key link between the brain and the endocrine system, a collection of glands in the body that make hormones. Hormones are substances that are released into the blood and stimulate other organs to work. The hypothalamus releases hormones into tiny blood vessels directly connected to the pituitary gland. These cause the pituitary gland to make its own hormones. The pituitary is considered the “master control gland” because the hormones it makes control the levels of hormones made by most other endocrine glands in the body.
The pituitary gland has 2 parts, the posterior pituitary and the anterior pituitary, each of which has a distinct function.
The smaller, back part of the pituitary gland, known as the posterior pituitary, is really an extension of brain tissue from the hypothalamus. The posterior pituitary is where the hormones made by the hypothalamus (vasopressin and oxytocin) are stored and released into the bloodstream.
- Vasopressin (also called antidiuretic hormone, or ADH) causes the kidney to retain water for the body and not lose it all in the urine. Without vasopressin, a person would urinate too much and become dehydrated. This condition is called diabetes insipidus. Vasopressin also can raise blood pressure by causing blood vessels to contract and narrow. It may have other functions as well.
- Oxytocin causes the uterus to contract in women during childbirth and the breasts to release milk when a woman nurses her baby. It may have other functions in both men and women as well.
Tumors rarely develop in the posterior pituitary.
Most pituitary tumors begin in the larger, front part of the pituitary gland known as the anterior pituitary. This is not brain tissue. It is a true gland. It makes several hormones that control other endocrine glands.
- Growth hormone (GH, also known as somatotropin) promotes body growth during childhood. If too much is made in a child they will grow very tall. Normally, adults make only small amounts of growth hormone. If an adult makes too much growth hormone, the bones of the hands, feet, and face continue to grow and become quite large, causing their normal features to become distorted. This condition is called acromegaly.
- Thyroid-stimulating hormone (TSH, also called thyrotropin) stimulates growth of the thyroid gland and the release of thyroid hormone. Thyroid hormone regulates metabolism. Too much makes you hyperactive and shaky, and too little makes you sluggish. Overproduction of TSH by a pituitary tumor is one cause of hyperthyroidism (an overactive thyroid gland).
- Adrenocorticotropic hormone (ACTH, also known as corticotropin) causes the adrenal glands to grow and to produce steroid hormones (such as cortisol). Too much of this hormone from the pituitary causes Cushing’s disease, the symptoms of which can include rapid weight gain and the buildup of fat in certain parts of the body.
- Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are also called gonadotropins. In women their main effects are on the ovaries, where they regulate ovulation (the release of eggs) and the production of the hormones estrogen and progesterone. In men, LH and FSH control testosterone and sperm production in the testicles.
- Prolactin causes milk production in the female breast. Its function in men is not known.
Almost all pituitary tumors are benign (non-cancerous) glandular tumors called pituitary adenomas. These tumors are considered benign because they don’t spread to other parts of the body, but they can still cause significant health problems because of their location near the brain and because many of them secrete excess hormones.
Pituitary cancers (called pituitary carcinomas) are very rare.
These benign tumors do not spread outside the skull. They usually remain confined to the sella turcica (the tiny space in the skull that the pituitary gland sits in). Sometimes they grow into the walls of the sella turcica and surrounding blood vessels, nerves, and coverings of the brain. They do not grow very large, but they can have a big impact on a person’s health.
There is very little room for tumors to grow in this part of the skull. Therefore, if the tumor becomes larger than about a centimeter (about half an inch) across, it can compress and cause damage to nearby parts of the brain and the nerves that arise from it.
The problems pituitary adenomas can cause include:
- Vision loss or double vision: The nerves that connect the brain to the eyes (the optic nerves) and to the muscles that move the eyes pass near the pituitary gland. An enlarged pituitary can press on these nerves and affect vision.
- Overproduction of hormones: Many pituitary adenomas make too much of a particular hormone, which can cause serious symptoms (see “How are pituitary tumors diagnosed?”).
- Hormone deficiency: Sometimes the pituitary adenoma can crowd out the healthy pituitary tissue that remains. Damage to this tissue can lead to a shortage of the other pituitary hormones.
Microadenoma versus macroadenoma
Pituitary adenomas can be divided into 2 categories based on size:
- Microadenomas are tumors that are smaller than 1 centimeter (cm) across. Because these tumors are small, they rarely damage the rest of the pituitary or nearby tissues. But they can cause symptoms if they release too much of a certain hormone into the bloodstream. Many people may actually have small adenomas that are never detected because they never grow large enough or secrete enough hormones to cause a problem.
- Macroadenomas are tumors 1 cm across or larger. Macroadenomas can affect a person’s health in 2 ways. First, they can cause symptoms if they make too much of a certain hormone. Second, they may cause symptoms by pressing on normal pituitary tissue or nearby nerves, such as the optic nerves.
Functional versus non-functional adenoma
Pituitary adenomas are also classified by whether they produce a hormone and, if they do, which type they make. If a pituitary adenoma makes hormones it is called functional. If it doesn’t make any hormones it is called non-functional.
Functional adenomas: Most of the pituitary adenomas that are found produce hormones. The hormones can be detected by blood tests or by tests of the tumor when it is removed with surgery. Based on these results, adenomas are classified as:
- Prolactin-producing adenomas (prolactinomas), which account for about 4 out of 10 pituitary tumors
- Growth hormone-secreting adenomas, which make up about 2 in 10 pituitary tumors
- Corticotropin (ACTH)-secreting adenomas (about 7%)
- Gonadotropin (LH and FSH)-secreting adenomas (less than 1%)
- Thyrotropin (TSH)-secreting adenomas (less than 1%)
Some adenomas secrete more than one type of hormone.
The kind of hormone an adenoma produces strongly affects what signs and symptoms the patient has. It also affects which tests are used for diagnosis, the choice of treatment, and the patient’s outlook.
Non-functional adenomas: Pituitary adenomas that do not make any hormone are called non-functional adenomas or null cell adenomas. They account for about 3 in 10 of all pituitary tumors that are found. They are usually detected as macroadenomas, causing symptoms because of their size as they press on surrounding structures.
Cancerous tumors of the pituitary gland are rare. Only a few hundred have ever been described in medical journals. They can occur at any age, but most are found in older people. These cancers usually make hormones, just like many adenomas do.
Most pituitary carcinomas look very much like pituitary adenomas under a microscope, so doctors have trouble telling them apart. In fact, there is no good way to tell if a pituitary tumor is a carcinoma and not an adenoma until the tumor spreads to another part of the body. If this happens, it is typically 5 to 10 years after the first surgery. Most often it spreads to the brain, spinal cord, meninges (the covering of the brain and spinal cord), or bone around the pituitary. Rarely, these cancers spread to other organs such as the liver, heart, or lungs.
Other pituitary tumors
There are several other types of benign pituitary tumors, as well as some malignant (cancerous) ones. All are much less common than adenomas.
Teratomas, germinomas, and choriocarcinomas are all rare tumors that usually occur in children or young adults. They do not develop from the endocrine cells of the pituitary gland itself, but they can grow into it and damage it.
Rathke cleft cysts and gangliocytomas of the pituitary are rare tumors that are usually found in adults.
Craniopharyngiomas are slow-growing tumors that start above the pituitary gland but below the brain itself. They may compress the pituitary gland and the hypothalamus, causing hormonal problems. They are more common in children, but they are sometimes seen in older adults.
Cancer that starts in sites other than the pituitary (like the breast) can metastasize (spread) to the pituitary. These cancers are classified and treated based on where they started (their primary site) and are not classified as pituitary tumors.
Last Medical Review: 01/11/2013
Last Revised: 01/11/2013