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 something about the pituitary gland and what it does.
The pituitary gland
The pituitary is a small gland at the base of the skull, just below the brain and above the nasal passages and 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 just above it.
The pituitary 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 and organs 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 to make its own hormones. The pituitary is considered the “master control gland” because it makes the hormones that control the levels of other hormones made by most of the endocrine glands in the body.
The pituitary gland has 2 parts, the anterior pituitary and the posterior pituitary. Each part has distinct functions.
The 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 several hormones:
- Growth hormone (GH, also known as somatotropin) promotes body growth during childhood. If a child or teen’s body makes too much growth hormone, they will grow very tall (a condition called gigantism). If an adult’s body makes too much growth hormone, the bones of the hands, feet, and face can grow larger than normal, distorting their features. This condition is called acromegaly.
- Thyroid-stimulating hormone (TSH, also called thyrotropin) stimulates the thyroid gland to release thyroid hormones, which regulate body metabolism. Too much of these hormones 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 make steroid hormones (such as cortisol). Too much ACTH from a pituitary tumor 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, as well as high blood pressure and diabetes.
- 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. Pituitary tumors that make prolactin can cause reproductive problems, as well as milk production in both women and men.
The posterior pituitary
The smaller, back part of the pituitary gland is really an extension of brain tissue from the hypothalamus. The posterior pituitary stores and releases hormones made by the hypothalamus (vasopressin and oxytocin) into the bloodstream.
- Vasopressin (also called antidiuretic hormone, or ADH) causes the kidneys to keep water in the body, rather than losing it all in the urine. When vasopressin levels are low, a person urinates too much and becomes dehydrated. This condition is called diabetes insipidus. Vasopressin also can raise blood pressure by constricting blood vessels. 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 also have other functions in both men and women.
Tumors rarely start in the posterior pituitary.
Almost all pituitary tumors are benign (not cancer) glandular tumors called pituitary adenomas. These tumors don’t spread to other parts of the body, like cancers can. Still, even benign pituitary tumors can cause major health problems because:
- They might press on nearby parts of the brain and important nerves.
- They may invade nearby structures (like the skull or the sinuses).
- Many pituitary tumors make excess hormones.
Pituitary cancers (called pituitary carcinomas) are very rare.
Pituitary adenomas are also known as pituitary neuroendocrine tumors (PitNETs). These benign tumors do not grow 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 bony walls of the sella turcica and nearby tissues, like blood vessels, nerves, and sinuses. They usually don’t grow very large, but they can still 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 classified by size:
- Microadenomas are tumors that are smaller than 1 centimeter (cm) across (less than 1/2 an inch). 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 any of the pituitary hormones. Many people actually have small adenomas that are never found because they don’t grow large enough or make enough hormones to cause any problems.
- Macroadenomas are tumors 1 cm across or larger. Macroadenomas can cause symptoms if they press on nearby structures such as normal parts of the pituitary or on nearby nerves. They can also sometimes cause symptoms if they make too much of a certain hormone.
Functional or non-functional adenomas
If a pituitary adenoma makes too much of a hormone, it’s called a functional (or functioning) adenoma. If it doesn’t make enough hormones to cause symptoms, it’s called a non-functional (or non-functioning) adenoma.
Functional adenomas: Most pituitary adenomas that cause symptoms make excess hormones:
- Lactotroph adenomas (prolactinomas) make prolactin. They account for about 4 out of 10 pituitary tumors.
- Somatotroph adenomas make growth hormone (GH). They make up about 2 in 10 pituitary tumors.
- Corticotroph adenomas make ACTH. They account for about 1 in 10 pituitary tumors.
- Gonadotroph adenomas make LH and FSH. Functional gonadotroph adenomas are very rare.
- Thyrotroph adenomas make TSH. They are very rare.
- Plurihormonal adenomas make more than one hormone. The most common of these are lactotroph/somatotroph adenomas, which make both prolactin and growth hormone.
The kind of hormone an adenoma makes strongly affects what signs and symptoms it causes. It also affects which tests are used for diagnosis, as well as treatment options.
Non-functional adenomas: These pituitary adenomas don’t make enough excess hormones to cause symptoms. Most often these are gonadotroph adenomas that don’t make enough hormones to cause any problems.
Non-functional adenomas account for about 3 in 10 of all detected pituitary tumors. By the time they are found, they usually have grown to be macroadenomas, causing symptoms because of their size as they press on nearby structures.
Cancers of the pituitary gland (known as pituitary carcinomas or metastatic PitNETs) are very rare. 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 for sure 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 carcinomas spread 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 tumors of the pituitary region
Several other types of benign and malignant (cancerous) tumors can grow in the region of the pituitary. All of these are much less common than pituitary adenomas.
Teratomas, germinomas, and choriocarcinomas are rare germ cell 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).