Pituitary tumors are classified according to size:
Microadenomas are smaller than 10 millimeters.
Macroadenomas are 10 millimeters or larger.
Most pituitary adenomas are microadenomas.
Once a pituitary tumor is found, more tests will be done to find out how far the tumor has spread, the type of tumor, and whether or not it makes hormones. A doctor needs to know the type of tumor to plan treatment. The following types of pituitary tumors are found:
These tumors make prolactin, a hormone that stimulates a woman’s breasts to make milk during and after pregnancy. Prolactin-secreting tumors can cause the breasts to make milk and menstrual periods to stop when a woman is not pregnant. In men, prolactin-producing tumors can cause impotence.
These tumors make a hormone called adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands to make glucocorticoids. When the body makes too much ACTH, it causes Cushing disease. In Cushing disease, fat builds up in the face, back, and chest, and the arms and legs become very thin. Another symptom of ACTH-producing tumors is weakened bones.
Growth hormone-producing tumors
These tumors make growth hormone. Too much growth hormone can cause acromegaly (the hands, feet, and face are larger than normal) or gigantism (the whole body grows much larger than normal).
Nonfunctioning pituitary tumors
Nonfunctioning tumors do not produce hormones. Symptoms such as headache or trouble seeing may be caused by the tumor pressing on nearby brain tissue. If the tumor presses on or destroys parts of the pituitary gland, the pituitary gland may stop making one or more of its hormones. Lack of a certain hormone will affect the work of the gland or organ that the hormone controls. For example, if the pituitary gland stops making the hormone that affects the ovaries, the ovaries will not work normally or will not develop normally in a child.
Thyroid-stimulating hormone-producing tumors
These tumors make thyrotrophin, which stimulates the thyroid gland to make thyroid hormone. The thyroid hormone helps regulate heart rate, body temperature, the level of calcium in the blood, and the rate at which food is changed into energy. Too much thyroid hormone can cause rapid heartbeat, weight loss, and other symptoms. Thyroid-stimulating hormone-producing tumors may be large and may spread. They sometimes also make growth hormone and/or prolactin.
These tumors usually grow quickly and make hormones, commonly ACTH and prolactin. Symptoms may be caused by the hormone that is made by the tumor and by the tumor pressing on nearby brain tissue.
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