Table 26-1 PITUITARY ADENOMAS pe Frequency (% Prolactin cell adenoma 20-30 Growth hormone cell adenomas 5 Mixed growth hormone-prolactin adenomas 5 ACTH cell adenomas 10-15 Gonadotroph cell adenomas 10-15 Null cell adenomas 20 Thyroid-stimulating hormone cell adenomas Other plurihormonal adenomas 15 ACTH, adrenocorticotropic hormone Modified from Burger PC, Scheithaurer BW, Vogel FS: Pituitary neoplasia. In Surgical Pathology of the Nervous System and its Coverings, 3rd ed. New York, Churchill Livingstone, 1991