Abstract
The new WHO classification of pituitary adenomas, which will be published in autumn 2004, is based on the histopathological classification of Kovacs et al. and include growth hormone (GH) producing adenoma, prolactin (PRL) producing adenoma, thyroid stimulating hormone (TSH) producing adenoma, adrenocorticotropic hormone (ACTH) producing adenoma, gonadotroph adenoma, null cell adenoma, and unusual plurihormonal adenoma. GH producing adenomas are further subdivided into 5 types : densely granulated somatotroph adenoma, sparsely granulated somatotroph adenoma, mammosomatotroph adenoma, mixed somatotroph-lactotroph adenoma, and acidophil stem cell adenoma. The latter 3 subtypes produce GH and PRL simultaneously. ACTH producing adenomas contain silent ACTH producing adenoma and Crooke's cell adenoma and silent ACTH producing adenomas are further subdivided into subtype 1 and subtype 2 adenomas according to electron microscopic findings. Gonadotroph adenomas are mostly clinically non-functioning adenomas and the most frequent type (about 30% of surgically resected adenomas). Null cell adenomas are defined as tumors negative for all adenohypophysial hormones and related transcription factors. Oncocytoma is classified as a subtype of null cell adenoma. Unusual plurihormonal adenomas include a rare type of silent subtype 3 adenoma, which is clinically similar to prolactinoma and often shows GH, PRL, and/or TSH immunoreactivity. Ptuitary carcinomas are defined as tumors that metastasize to extracranial organs and menincus, and are highly malignant. They show numerous mitosis, cellular atypia and necrotic foci in metastatic lesions but it is hard to see these figures in the primary sites. Atipcal adenomas are introduced as a model to see the possibility for potential metastatic ability, and the presence of mitosis and P53 protein-positive cells and a Ki-67 labelling index of more than 3% are their indicators.
