The pituitary gland

The pituitary gland is found inside the skull just above the nasal passages, which are above the fleshy back part of the roof of the mouth. It sits in a tiny bony space called the sella turcica. This small gland is connected directly to part of the brain called the hypothalamus. This connection to the hypothalamus provides a key link between brain activity and the endocrine (hormone-producing gland) system.

The hypothalamus releases substances called hormones that directly affect the pituitary gland. Hormones are substances that are released into the blood and stimulate other organs to work. The hypothalamus releases its hormones into a tiny blood channel directly connected to the pituitary gland. These cause the pituitary gland to make its own hormones. The pituitary is considered the "master control gland" of hormone production because it regulates the activity of most other glands in the body.

Pituitary hormones

The pituitary gland has 2 parts -- the posterior pituitary and the anterior pituitary -- each with distinct functions.

Posterior pituitary

The smaller posterior pituitary (back part of the pituitary gland) is really an extension of brain tissue. The posterior pituitary is where the hormones vasopressin (also called antidiuretic hormone, or ADH) and oxytocin are made and released into the bloodstream.

• Vasopressin causes the kidney to retain water for the body and not lose it all in the urine. Without vasopressin, a person would urinate (pee) 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.

• Oxytocin causes the uterus to contract during childbirth and the breasts to release milk when a woman nurses her baby.

Tumors rarely develop in the posterior pituitary.

Anterior pituitary

Most pituitary tumors begin in the larger anterior pituitary (front part of the pituitary gland). This is not brain tissue. It is a true gland. It produces several hormones that control other endocrine (hormone-producing) 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 continues to make 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 adrenal gland growth and production of steroid hormones (such as cortisone) by the adrenal glands. Too much of this hormone from the pituitary produces a disease called Cushing's disease, named after the famous neurosurgeon, Harvey Cushing, who first described it.

• Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are also called gonadotropins. They regulate ovulation and the hormones estrogen and progesterone in women. In men, LH and FSH control testosterone and sperm production in the testicles.

• Prolactin, another pituitary hormone, causes milk production in the female breast. Its function in men is not known.

Pituitary tumors

Almost all pituitary tumors are benign (non-cancerous) glandular tumors called adenomas.

Pituitary carcinomas

Cancerous tumors of the pituitary gland (called pituitary carcinomas) are rare. Only about 140 have been described in medical journals. Although they can occur at any age, most are found in older persons. Most of them make hormones -- just like adenomas do. Most pituitary carcinomas look very much like large pituitary adenomas. 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. Most often it spreads to the brain, spinal cord, meninges (the layer of tissue that covers the brain and spinal cord), or bone around the pituitary. These cancers rarely spread to the liver, ovaries, heart, or lungs. Often, when these tumors are first removed, they are thought to be an adenoma (benign). It is only when the tumor comes back at a distant location, that the doctors realize that it is a carcinoma. This typically happens 5 to 10 years after the first surgery.

Pituitary adenomas

These benign tumors do not spread outside the skull. They usually remain confined to the sella turcica (the tiny bony space that the pituitary gland sits in). Sometimes they grow into the walls of the sella turcica and surrounding vessels, nerves, and coverings of the brain. Although they do not grow very large, 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 an inch, it can compress and cause damage to nearby parts of the brain.

• Vision loss: the nerves leading to the eye pass by the pituitary gland. An enlarged pituitary can press on these nerves and affect vision.

• Overproduction of hormones: many adenomas produce and release too much pituitary hormone, which can cause serious symptoms.

• 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.

Pituitary adenomas are divided into 2 categories by size:

• Tumors that are smaller than 1 cm (a little less than 1/2 inch) are called microadenomas. Because these tumors are small, they rarely damage the rest of the pituitary or neighboring tissues. They produce symptoms because they release too much of a certain hormone into the bloodstream.

• Tumors larger than 1 cm are called macroadenomas. Macroadenomas can affect a person’s health in 2 ways. First, they can cause symptoms if they make a hormone. Second, they may cause symptoms by pressing on normal pituitary tissue or nearby nerves, such as the optic nerve (responsible for vision).

In the past, pituitary tumors were classified by their appearance under the microscope after they were removed by surgery. They were classified into 3 types. Basophilic adenomas had blue cells, acidophilic adenomas had pink/red cells, and chromophobe adenomas had relatively colorless cells. This system is no longer considered the best way to classify these tumors.

Now, adenomas are classified by whether they produce a pituitary hormone and, if they do, which type they produce. If a pituitary adenoma makes hormone it is called functional. If it doesn't make any hormone it is called non-functional. Most of the pituitary adenomas that are found produce hormones. The hormone production 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 -- about half of the pituitary tumors that make hormones produce prolactin)
• growth hormone-secreting adenomas (close to a third of the hormone-producing pituitary tumors)
• corticotropin (ACTH)-secreting adenomas (about 20%)
• gonadotropin-secreting adenomas (less than 1%)
• thyrotropin (TSH)-secreting adenomas (rare, about 3%)

There are also null cell adenomas. These tumors, which account for about 20% of all pituitary tumors, do not make any hormone. Knowing what kind of hormone an adenoma produces is important because the hormone strongly affects what signs and symptoms the patient has. This also affects which tests are used for diagnosis, the choice of treatment, and the patient's outlook.

Other pituitary tumors

There are several other types of benign pituitary tumors, as well as some malignant ones. All are much less common than adenomas. Teratomas, germinomas, and choriocarcinomas are all rare tumors that usually occur in children or young adults. Although they do not develop from the pituitary gland itself, 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.

Cancer that starts growing in sites other than the pituitary (like the breast) can metastasize (spread) to the pituitary. These cancers are classified by where they started growing (their primary site) and are not classified as pituitary tumors.

Last Medical Review: 02/17/2009
Last Revised: 02/17/2009