Ultrastructural and immunoelectron microscopic study of three unusual plurihormonal pituitary adenomas

Monomorphous pituitary adenomas expressing several hormones by immunocytoch emistry are common, whereas adenomas displaying multiple immunoreactivities and consisting of more than one morphologic cell types are rare. Three suc h unusual pituitary adenomas, surgically removed from two patients with acr omegaly and one patient with hyperprolactinemia, were investigated by histo logy, immunocytochemistry, transmission electron microscopy, as well as imm unoelectron microscopy using double immunogold labeling. Immunocytochemistr y revealed variable degrees of immunoreactivities for growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (beta-TSH), and alpha-subunit of glycoprotein hormones in all three tumors. The three adenomas consisted of phenotypically diverse cell populations as documented by transmission el ectron microscopy. In addition to monohormonal GH cells, immunoelectron mic roscopy demonstrated numerous cells colocalizing GH and PRL or GH and beta- TSH, and rarely PRL and beta-TSH in tumors of acromegalics. The adenoma cau sing hyperprolactinemia consisted chiefly of mammosomatotrophs colocalizing PRL and GH, whereas beta-TSH labeling was scant. The three tumors in the s tudy were selected from a cluster of five plurimorphous plurihormonal adeno mas received from the same locale where they accounted for an unprecedented 21% of adenomas producing GH and/or PRL. The enhanced susceptibility to de velop plurimorphous adenomas of the acidophil cell line may have a genetic basis in the stable population the patients came from.