A pituitary adenoma is a slow-growing, benign type of brain tumor that develops from specialized cells in the pituitary gland, which sits at the base of the brain, explains UCLA Health. Pituitary adenomas can secrete hormones or be clinically nonfunctioning, meaning they do not produce excess amounts of active hormones.
The type of hormone a functioning pituitary adenoma secretes depends on the type of pituitary cell from which it originated, notes UCLA Health. A prolactinoma is a type of pituitary adenoma that secretes the hormone prolactin. When a pituitary adenoma produces excess amounts of growth hormone in adults, a condition called acromegaly results. Gigantism is the name of the condition that results when a child has too much growth hormone due to a pituitary adenoma. Cushing's disease is another example of a disease that results from an overabundance of a hormone, specifically cortisol, from a functioning pituitary adenoma.
One in five adults has a pituitary adenoma, but most of the tumors are very small and do not produce symptoms, states UCLA Health. When they are symptomatic, the symptoms depend both on the type of hormone involved, if any, and the size of the tumor. A particularly large tumor can press against the optic chiasm, producing vision loss or other vision-related problems. A tumor can also compress the pituitary gland, resulting in a reduction in normal hormone production.