How are pituitary adenomas classified?
Pituitary adenomas are characterized as follows:
• Cell of origin: Gonadotroph, lactotroph, somatotroph, corticotroph, or thyrotroph-derived as determined by immunohistochemical staining for the pituitary hormones and the transcription factors that determine pituitary cell lineages (e.g., T-Pit = corticotrophs; SF-1 = gonadotrophs; and Pit-1 = thyrotrophs, somatotrophs, and lactotroph cells).
• Size: Microadenomas < 1 cm; macroadenomas ≥ 1 cm; and giant adenomas > 4 cm.
• Clinical evidence of hormone over-production: As discussed in the other chapters, pituitary tumors may manifest with clinically distinct syndromes on the basis of their hormone production (e.g., growth hormone [GH] tumors = acromegaly; adrenocorticotropic hormone [ACTH] tumors = Cushing’s disease; prolactinoma = galactorrhea [in females]. In contrast, a nonfunctional adenoma (NFA) is characterized by the clinical absence of pituitary hormone excess. Most NFAs are of gonadotroph origin but are not clinically apparent because of inefficient synthesis or secretion of intact follicle-stimulating hormone-beta (FSH-beta) or luteinizing hormone-beta (LH-beta) molecules with the alpha subunit glycoprotein.