What Are Pituitary Tumors?

A tumor is an abnormal growth of cells. Tumors can start nearly anywhere in the body. Tumors that start in the pituitary gland are called pituitary tumors.

To understand pituitary tumors, it helps to know about the normal pituitary gland and what it does.

The pituitary gland

The pituitary is a small gland found inside the skull just below the brain and 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 released into the blood that control how other organs work. The hypothalamus releases hormones into tiny blood vessels connected to the pituitary gland. These then cause the pituitary gland to make its own hormones. The pituitary is considered the “master control gland” because it makes the hormones that control the levels of hormones made by most of the other endocrine glands in the body.

The pituitary gland has 2 parts, the anterior pituitary and the posterior pituitary. Each has distinct functions.

Anterior pituitary

Most pituitary tumors start in the larger, front part of the pituitary gland known as the anterior pituitary. This part of the gland makes these 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. If a pituitary tumor makes too much TSH, it can cause hyperthyroidism (an overactive thyroid gland).
  • Adrenocorticotropic hormone (ACTH, also known as corticotropin) causes the adrenal glands to grow and to make steroid hormones (such as cortisol). Too much ACTH from the pituitary causes Cushing’s disease, the symptoms of which can include rapid weight gain and the build-up 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 control 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.

Posterior pituitary

The smaller, back part of the pituitary gland, called the posterior pituitary, is really an extension of brain tissue from the hypothalamus. The posterior pituitary is where hormones made by the hypothalamus (vasopressin and oxytocin) are stored and released into the bloodstream.

  • Vasopressin (also called antidiuretic hormone, or ADH) causes the kidneys to keep water in the body and not lose it all in the urine. Without vasopressin, a person urinates too much and becomes dehydrated. This condition is called diabetes insipidus. Vasopressin also can raise blood pressure by causing blood vessels to constrict. It might 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 might have other functions as well.

Tumors rarely start in the posterior pituitary.

Pituitary tumors

Almost all pituitary tumors are benign (not cancer) glandular tumors called pituitary adenomas. These tumors are called benign because they don’t spread to other parts of the body, like cancers can. Still, even benign pituitary tumors can cause major health problems because they are close to the brain, may invade nearby tissues (like the skull or the sinuses), and because many of them make excess hormones.

Pituitary cancers (called pituitary carcinomas) are very rare.

Pituitary adenomas

These benign tumors do not spread outside the skull. They usually stay in the sella turcica (the tiny space in the skull that the pituitary gland sits in). Sometimes they grow into the boney walls of the sella turcica and nearby tissues, like blood vessels, nerves, and sinuses. They don’t 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. So, if the tumor gets larger than about a centimeter (about half an inch) across, it may grow upward, where it can press on and damage nearby parts of the brain and the nerves that arise from it. This can lead to problems like vision changes or headaches. (See Signs and Symptoms of Pituitary Tumors.)

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 make too much of a certain hormone. Many people actually have small adenomas that are never found because they don't grow large enough or make 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 can cause symptoms by pressing on normal parts of the pituitary or on nearby nerves, such as the optic nerves.

Functional versus non-functional adenoma

Pituitary adenomas are also classified by whether they make too much of a hormone and, if they do, which type they make. If a pituitary adenoma makes too much of a hormone it's called functional. If it doesn’t make enough hormones to cause problems it's called non-functional.

Functional adenomas: Most of the pituitary adenomas that are found make excess 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, pituitary adenomas are classified as:

  • Lactotroph adenomas make prolactin and account for about 4 out of 10 pituitary tumors.
  • Somatotroph adenomas make growth hormones and make up about 2 in 10 pituitary tumors.
  • Corticotroph adenomas make ACTH and account for about 1 in 10 pituitary tumors.
  • Gonadotroph adenomas make LH and FSH and are very rare.
  • Thyrotroph adenomas make TSH and are very rare.
  • Plurihormonal adenomas make more than one hormone.
  • Null cell adenomas do not make hormones. (These are non-functional adenomas.)

The kind of hormone an adenoma makes strongly affects what signs and symptoms it causes. It also affects which tests are used for diagnosis, the choice of treatment, and the patient’s outlook.

Non-functional adenomas: Pituitary adenomas that don’t make excess hormones 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 found as macroadenomas, causing symptoms because of their size as they press on nearby structures.

Pituitary carcinomas

Cancers 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.

Pituitary carcinomas look like pituitary adenomas under a microscope, so doctors have trouble telling them apart. In fact, the only way to tell if a pituitary tumor is a carcinoma and not an adenoma is when the tumor spreads to another part of the body not near the pituitary gland. Most often pituitary carcinoma 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.

One of the key issues with pituitary tumors is that there's currently no way to know if a benign pituitary adenoma will become cancer and grow and spread to other parts of the body.

Other tumors of the pituitary region

There are several other types of benign tumors that grow in the region of the pituitary, as well as some malignant (cancerous) ones. All are much less common than pituitary adenomas.

Teratomas, germinomas, and choriocarcinomas are all rare tumors that usually occur in children or young adults. They don’t develop from the hormone-making cells of the pituitary gland itself, but they can grow into the pituitary 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 sometimes press on the pituitary and the hypothalamus, causing hormone problems. They're more common in children, but they can be seen in older adults. For more on these tumors, see Brain and Spinal Cord Tumors in Children.

Cancers that start in some other parts of the body (like the breast) can sometimes spread to the pituitary. These cancers are classified and treated based on where they started (their primary site) and are not thought of as pituitary tumors.

The rest of our information focuses mainly on benign pituitary tumors (pituitary adenomas).

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Revised: November 2, 2017

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