RESUMO
In material of 347 surgically removed pituitary adenomas, 15 tumors (4.3%) were diagnosed as acidophil stem cell adenomas. These are immature neoplasms, assumed to derive from the common progenitor of growth hormone and prolactin cells, and usually containing both hormones by the immunoperoxidase technique. Clinically, they are regularly associated with hyperprolactinemia. Some patients may exhibit physical stigmata of acromegaly without biochemical evidence of the disease ("fugitive acromegaly"). The entity is also characterized by (1) relatively short clinical history; (2) large (grade III--IV), locally invasive adenoma, and (3) relatively low hormonal activity. By electron microscopy, these tumors are unicellular with immature cytoplasm, exhibiting some features of adenomatous growth hormone and prolactin with immature cytoplasm, exhibiting some features of adenomatous growth hormone and prolactin cells and frequently mitochondrial abnormalities as well. They are more aggressive than the well-differentiated adenomas of the "acidophil" cell line--a fact to be considered in postoperative management.