The pituitary gland is a pea-sized gland that sits just below the brain, roughly behind the bridge of the nose. Despite its small size, the pituitary is often called the “master” gland because it produces hormones that regulate the activity of other hormone-producing glands in the body, including the adrenal and thyroid glands, as well as the gonads (the ovaries and testicles).

The pituitary plays a role in many essential physiologic processes, including regulation of growth, blood pressure, metabolism, sperm and egg production, and much more. Occasionally, however, these functions can be disrupted when a tumor starts growing in the pituitary.

Fortunately, effective treatments including surgery, radiation, and medications are available. At Yale Medicine, endocrinologist, neurosurgeons, and ear-nose-and-throat surgeons come together to diagnose and treat pituitary tumors. "We have all of the necessary subspecialties to act as a unit, and on top of that, our capabilities in the operating room are advanced," explains Yale Medicine neurosurgeon Sacit Bulent Omay, MD. "We have an intraoperative magnetic resonance imaging [MRI] system that can confirm that the tumor is totally removed before the surgery is concluded." 

Tumors form in the pituitary when cells in the gland grow in an abnormal and uncontrolled manner. These cells multiply and eventually form a mass of cells called a tumor.

Most pituitary tumors are benign, meaning they are not cancerous and do not spread to other parts of the body. Benign pituitary tumors are also known as pituitary adenomas (“adeno” means gland and “oma” means tumor). In rare cases, pituitary tumors may be cancerous. Cancerous pituitary tumors, known as pituitary carcinomas, make up only around 0.2% of all pituitary tumors.

Pituitary tumors fall into two broad categories:

• Functioning tumors produce and secrete hormones. The individual cells that make up the pituitary specialize in producing different hormones. When a tumor forms from one of these cells, it also produces the hormone made by that cell. Functioning tumors usually produce and secrete excessive levels of hormones, which can cause problems in other tissues and glands.
• Nonfunctioning tumors do not produce hormones. They can, however, become larger masses that affect surrounding nervous tissue. They make up about 30% of all pituitary tumors.

Pituitary tumors, whether functioning or nonfunctioning, are further classified based on their size.

• Microadenomas are tumors that are less than 1 cm in diameter.
• Macroadenomas measure over 1 cm in diameter. Depending on its location, if a tumor grows large enough, it can press against nearby tissues, such as the optic nerves or other parts of the brain, resulting in vision and other problems. Pituitary tumors can also compress the tissue of the pituitary gland itself, which can impair the gland’s ability to produce one or more hormones.

There are several types of functioning pituitary tumors. They are classified by the type of hormone they make.

• Prolactin-producing adenomas (prolactinomas). These account for around 40% of pituitary tumors. They make and secrete excess prolactin, the hormone that stimulates the production of breast milk. These tumors affect women and men.
• Growth hormone-secreting adenomas (somatotrophs). These make up around 20% of functional tumors. When a tumor makes too much growth hormone, it can cause excessive growth of bones and joints, as well as other tissues.
• Adrenocorticotropin-secreting adenomas (ACTH-secreting adenomas). Some pituitary tumors secrete a hormone known as adrenocorticotropic hormone, or ACTH, which regulates the adrenal gland’s production of hormones. These include cortisol, which is key to the body’s stress and immune responses, as well as the regulation of blood pressure, blood sugar levels, and metabolism.
• Thyrotropin-secreting adenomas (TSH-secreting adenomas). These produce a hormone called thyroid stimulating hormone, or TSH, which stimulates the thyroid gland to secrete thyroid hormones, which in turn play a role in regulating the body’s basal metabolic rate as well as heart rate, body temperature, and weight.
• Gonadotropin-secreting adenomas. These tumors secrete gonadotropins, a class of hormones that includes follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH are involved in the production of sex hormones. They regulate sperm production in men and the production and release of eggs from the ovaries in women.
• Multihormonal adenomas. These uncommon pituitary tumors secrete more than one type of hormone.

Most pituitary tumors are sporadic, meaning they occur in people who do not have any known hereditary condition associated with them. In rare instances, some pituitary tumors are linked to genetic conditions, including multiple endocrine neoplasia type 1 (MEN1) and type 4 (MEN4), McCune-Albright-syndrome, familial isolated pituitary adenoma (FIPA), and Carney complex.

Nothing related to lifestyle or environmental factors is known to increase or decrease a person's chances of getting one.

Symptoms of functioning pituitary tumors vary based on the hormone or hormones that are overproduced:

• Prolactinoma. Premenstrual women may experience irregular or absent periods, discharge of breast milk when not pregnant or nursing, and infertility. Men may have low sex drive, erectile dysfunction, or breast growth. Prolactinomas can lead to osteoporosis in both men and women.
• Growth hormone-secreting adenomas. In children, excessive growth hormone can result in gigantism, a condition that causes them to grow much taller than normal. In adults, it can cause acromegaly, a condition marked by enlargement of the hands, feet, and some facial features. People with these conditions may experience joint pain, headaches, heart problems, sleep apnea, and high blood pressure, among other symptoms.

• ACTH-secreting adenomas. These tumors can cause Cushing disease, a condition characterized by weight gain, diabetes, high blood pressure, osteoporosis, easy bruising, stretch marks, and muscle weakness.
• TSH-secreting adenomas can lead to hyperthyroidism, a condition that can cause nervousness, muscle weakness, fatigue, weight loss, and diarrhea.
• Gonadotropin-secreting adenomas can cause irregular menstrual periods and infertility in premenopausal women. Men may develop enlarged testicles and low libido. Gonadotropin-secreting adenomas, however, usually don't usually secrete enough extra hormone to make a noticeable difference.

Pituitary tumors, whether nonfunctioning or functioning, can also cause symptoms if they grow large enough to press against nearby tissues. For instance, tumors that press against the pituitary gland can impair its ability to produce hormones. This results in low levels of one or more hormones. Depending on their size and where they are located, pituitary tumors can press against the optic nerves or other parts of the brain, resulting in vision problems and headaches.

Diagnosis of a pituitary tumor involves a review of the patient’s medical history, a physical exam, and tests including bloodwork and imaging tests.

The doctor will ask about the patient’s symptoms, perform a physical exam, and check for signs that may be caused by pituitary tumors.

If a patient has symptoms or signs that might suggest a tumor, blood and urine tests can measure the levels of different hormones. An eye exam may also be needed to determine whether a tumor is causing vision problems.

Imaging tests allow doctors to visualize pituitary tumors and are usually necessary for diagnosis. A magnetic resonance imaging (MRI) scan is the most commonly used imaging test for diagnosing pituitary tumors, but sometimes a computed tomography (CT) scan is used.

Depending on the size and type of pituitary tumor, treatment may involve the following:  

• Monitoring. Some small pituitary tumors may not cause any symptoms. In such cases, doctors may decide to monitor the tumor with periodic checkups and MRI scans. If symptoms develop, other treatments can be initiated promptly.
• Surgery. Many tumors can be removed through a procedure known as endoscopic endonasal surgery. In this procedure, an ENT (ear, nose, and throat) surgeon inserts an endoscope—a tiny tube equipped with a camera—through the nasal passages and sphenoid sinus, an air-filled cavity close to the pituitary gland. Then, the neurosurgeon uses special instruments to remove the pituitary tumor using minimally invasive techniques.
• Radiation therapy. This treatment uses radiation to kill tumor cells. It may be used after surgery to remove any tumor cells that remain, in combination with medications, or on its own, to shrink or destroy the tumor. This method is usually reserved for recurrent smaller tumors.
• Medications. Various types of medications are used to treat functioning pituitary tumors. Some of these medications work by shrinking tumors or preventing them from growing. Others suppress tumor secretion of hormones or block the action of hormones on other tissues in the body.
  
• Chemotherapy. Cancerous pituitary tumors may be treated with chemotherapy, which are drugs that destroy cancer cells.

The outlook depends on a number of factors including the type of tumor and its size. Most pituitary tumors, though, are treatable and many can be cured. Tumors that grow large enough to press against the optic nerves or parts of the brain can cause lasting damage and symptoms. 

Similarly, the hormones secreted by functioning tumors may result in long-term and potentially serious symptoms. In general, outcomes are best when tumors are detected and treated early.

Following initial treatment, some people may need to may need to take supplementary hormones for life. In all cases, people should see their doctors regularly to monitor hormone levels and check for recurrence of the tumor.

"We are a referral center for pituitary cases," Dr. Omay says. "And another thing we offer here is a look at the genetic profile of the tumor. We are hoping, with more research, to be able to find special targets for medications that these tumors will be vulnerable to, and it's an ongoing process."