Definition of Hypopituitarism:

Hypopituitarism is a condition in which the pituitary gland does not produce normal amounts of some or all of its hormones.

Causes, incidence, and risk factors:

The pituitary gland is a small structure that is located just below the brain. It is attached by a stalk to the hypothalamus, the area of the brain that controls its function.

The hormones released by the pituitary gland (and their functions) are:

• Adrenocorticotropic hormone (ACTH) -- stimulates the adrenal gland to release cortisol; cortisol helps to maintain blood pressure and blood sugar
• Antidiuretic hormone (ADH) -- controls water loss by the kidneys
• Follicle stimulating hormone (FSH) -- controls sexual function and fertility in males and females
• Growth hormone (GH) -- stimulates growth of tissues and bone
• Luteinizing hormone (LH) -- controls sexual function and fertility in males and females
• Oxytocin -- stimulates the uterus to contract during labor and the breasts to release milk
• Prolactin -- stimulates female breast development and milk production
• Thyroid stimulating hormone (TSH) -- stimulates the thyroid gland to release hormones that affect the body's metabolism

In hypopituitarism, there is a lack of one or more pituitary hormones. Lack of the hormone leads to loss of function in the gland or organ that it controls. For example, no TSH leads to loss of function in the thyroid gland.

Hypopituitarism may be caused by:

• Brain surgery
• Brain tumor
• Head trauma
• Infections of the brain and the tissues that support the brain
• Radiation
• Stroke
• Subarachnoid hemorrhage (from a burst aneurysm)
• Tumors of the pituitary gland or hypothalamus

Occasionally, hypopituitarism is due to uncommon immune system or metabolic diseases, such as:

• Hemochromatosis
• Histiocytosis X
• Lymphocytic hypophysitis
• Sarcoidosis

Hypopituitarism is also a rare complication after pregnancy, a condition called Sheehan's syndrome.