What is a Pituitary Microadenoma?

A pituitary microadenoma is a very small, noncancerous tumor that forms in the pituitary gland. It is medically defined as a mass that is less than about 1 centimeter (10 millimeters) in diameter that grows slowly and does not carry any risk of metastasizing, or spreading, to other parts of the brain or body.

While pituitary microadenomas are benign, they can still cause problems if they disrupt normal hormone production. A microadenoma may increase or alter levels of growth hormone, thyroid stimulating hormone (TSH) adrenocorticotropic hormone (ATCH), or prolactin. Symptoms can vary widely and occasionally become life threatening, but early diagnosis and treatment with medications or surgery can prevent most patients from suffering major complications.

It is often difficult to find an underlying cause for a pituitary microadenoma. Genetic factors are most likely the main contributing cause, but doctors have not yet identified specific mutations or genetic patterns that lead to the development of the tumors. The majority of people who get this tumor are over the age of 60. Females are slightly more susceptible than males for reasons that are not entirely clear.

Some microadenomas do not alter hormone secretion but still cause general symptoms, such as headaches, vision disturbances, and nausea. A pituitary microadenoma that increases prolactin levels can cause erectile dysfunction in men, absent periods in women, or total infertility in either sex. Overproduction of growth hormone may lead to acromegaly, a chronic condition in which body tissues and bones grow uncontrollably and cause disfigurement. Serious adrenal gland and thyroid problems can occur with ATCH- and TSH-producing tumors, respectively.

Diagnosing a pituitary microadenoma involves reviewing a patient's full medical and familial history and performing a series of tests. Blood tests may reveal unusual hormone activity and possible genetic abnormalities. Tumors can usually be seen on computerized tomography scans and other imaging tests, though sometimes an exploratory surgical procedure is needed to locate a very small mass. Treatment decisions can be considered once a microadenoma is discovered and all symptoms have been identified.

Surgery to remove a pituitary microadenoma is the treatment of choice in most cases, though it is not always possible because of patients' overall health or specific underlying conditions. In addition, it is possible that a tumor can return after it has been removed. When surgery is not advisable or ineffective, patients generally begin daily drug regimens with medications designed to block the particular hormones that are being over-secreted. Some people need to take medications for the rest of their lives to prevent symptoms from worsening or returning.