The pituitary gland, located at the base of the brain, is a small organ about the size of an acorn. It is surrounded by a bony saddle-like structure above the sinuses at the back of the nose, called the sella turcica. The pituitary gland is sometimes referred to as the "master gland" because it releases substances, which control the basic functions of growth, metabolism, and reproduction.
The pituitary gland is divided into two parts called lobes. These are referred to as the anterior and posterior lobes. Each lobe releases special substances, or hormones, which control basic activities within the body. The specific hormones and their activities are shown below.
The pituitary gland is responsible for regulating many body tissues. Breast function in females, steroid production by adrenal glands, thyroid function, bone growth and health, sexual function in men and women, fluid and electrolyte and water balance, and contraction of the uterus during childbirth are just some of the functions that it regulates. There is a complex balance of feedback loops between the various body organs and the pituitary that enables the body to function optimally.
What is a Pituitary Tumor?
Pituitary tumors can grow inside or on the surface of your pituitary gland. Because the pituitary gland is located just below the optic (vision) nerves, pituitary tumors can cause vision problems, including partial loss of vision and even blindness.
View our infographic and learn more about causes, detection and treatment of pituitary tumors.
Signs and Symptoms
A tumor in the pituitary gland causes symptoms by either releasing too much of a hormone or by pressing on the gland causing it to release too little hormone. The symptoms one experiences from the pituitary tumor are often determined by the type of tumor. A tumor that secretes hormones produces symptoms by releasing too much of the hormone. Some tumors cause the gland to stop releasing enough hormones. In this case symptoms arise from lack of hormones. A pituitary tumor may also cause symptoms by growing and pressing on the structures, like the nerves to the eyes, surrounding the pituitary gland.
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Types of Pituitary Tumors
The pituitary gland produces hormones to regulate such body functions as growth, blood pressure and reproduction. Pituitary tumors are abnormal growths in your pituitary gland that may cause excessive production of hormones or restrict the gland’s normal production of hormones. Most pituitary tumors are adenomas, which are non-cancerous growths that do not spread to other parts of your body. Other types of pituitary tumors include pituitary carcinomas, Rathke's cleft cysts and craniopharyngiomas
The cause of pituitary tumor is unknown. A small number of these tumors seem to be hereditary. They can occur at any age but are more likely to appear in older adults.The symptoms of pituitary tumors are related to the pressure the tumor exerts on the rest of the gland and nearby structures; this pressure affects the amount of hormones your gland produces.
If the tumor is producing hormones (known as a functioning tumor), the type of hormone it is producing will determine your symptoms.
- Adrenocorticotropic hormone - secreting tumors stimulate your adrenal glands to make cortisol and may result in Cushing’s syndrome in which fat accumulates around your midsection and upper back, your face gets rounder, you may develop a hump on your upper back, you can experience high blood pressure and blood sugar, your muscles may weaken, your skin may thin and bruise more easily and you may become more anxious, depressed or irritable.
- Growth hormone - secreting tumors may cause acromegaly which may coarsen your facial features, enlarge your hands and feet, cause excess sweating, cause high blood sugar, create heart problems and joint pains and increase the growth of body hair.
- Prolactin - secreting tumors (prolactinoma) can cause a decrease in the levels of sex hormones. Women may experience irregular menstrual periods or none at all and a milky discharge from their breasts. Men may experience erectile dysfunction, infertility and loss of sex drive.
- Thyroid - stimulating hormone-secreting tumors produce too much thyroxine, which may accelerate your body’s metabolism and cause sudden weight loss, a rapid or irregular heartbeat, nervousness and irritability, feeling too hot and frequent bowel movements.
Pituitary Hormones and Their Functions and Effects on the Body
The chart below summarizes the effects of the hormone of the pituitary gland on various bodily functions. Each hormone has a number of specialized effects, and this chart only summarizes these complicated hormonal interactions.
There is a delicate cycle of secretion and regulation of these functions that varies by time of day and the degree to which a person is physically and psychologically stressed. Each of these hormones can be tested using a variety of different studies. They can be tested by measuring the individual hormone levels in the blood, but they can also be tested by stimulation or suppression tests, which tell the doctors how well the body's balance and regulation of these hormones is working. We may also refer you to an endocrinologist for more testing.
|Thyroid Stimulating Hormone (TSH)||Causes the thyroid gland to grow and release thyroid hormones (called T4 and T3)|
|Adrenocorticotropic Hormone (ACTH)||Causes adrenal gland to release several hormones, particularly cortisol.|
|Growth Hormones (GH)||The main hormone for general body growth as well as regulation of glucose metabolism.|
|Follicle Stimulating Hormone (FSH)||Stimulates ovulation in women and the production of sperm in men.|
|Luteinizing Hormone (LH)||Stimulates ovulation in women and testosterone production in men.|
|Prolactin (PRL)||Elevated during pregnancy produces breast enlargement, lactation, and loos of menstrual cycle. Causes impotence in men|
|Antidiuretic Hormone (ADH)||Controls thirst and the amount fluid reabsorbed into the bloodstream and the amount of urine produced by the kidneys.|
|Oxytocin||Stimulates uterine contractions in women. Its function, if any, in men is unknown.|
Visual Problems from Pituitary Tumors
The pituitary gland is a about the size of an acorn; it is located at the base of the brain. Some of the symptoms a pituitary tumor can cause are due to its proximity to the optic nerves. Many types of visual problems can occur when a pituitary tumor grows upwards and presses on the optic nerves or their connections. The most common problem is to lose vision in the outer fields (peripheral vision), called a bitemporal hemianopsia. Often patients do not notice this, as they correct for the problem by moving their head back and forth. Doctors perform an examination called a visual field test in order to detect what quadrants of vision may not be functioning correctly. Loss of peripheral vision may occur first and be undetected. This may progress to eventual blindness if the pressure is not removed from the nerve. Almost any kind of visual problem can be seen with large pituitary tumors. The tumor may also press on the nerves that move the eye and cause double vision. If the tumor is very large, it may press on other parts of the brain and cause problems with memory, weakness or numbness.
Detecting and Diagnosing Pituitary Tumors
To make a diagnosis of a pituitary tumor, doctors must first determine the size and location of the pituitary tumor. To do that, they will order computed tomography (CT) and/or magnetic resonance imaging (MRI) scans. These scans will help your doctors plan your treatment. An ophthalmologist may also be consulted to perform visual acuity and field tests to determine whether the tumor is pressing on one or both optic nerves or other parts of the visual system. An endocrinologist will measure hormone levels in the blood and urine to see whether pituitary-related hormone levels are abnormal.
Our physicians at Houston Methodist specialize in treating pituitary tumors at the following convenient locations.