ACROMEGALY was first described by Marie more than 100 yr ago and is the consequence of GH hypersecretion. It is the second most common type of pituitary hypersecretory syndrome and isalmost always caused by a somatotroph adenoma. Recent epidemiologic studies have indicated anincidence rate 3.3 per million/yr and a prevalence rate of 66 per million (1). From both clinical and histopathologic criteria, GH secreting pituitary tumors are heterogeneous. The majority of tumors store relatively small quantities of GH, exhibit a moderate growth rate, and often exhibit extrasellar extension when initially diagnosed. In contrast, a smaller number of tumors exhibit a very slow growth rate, contain high concentrations of GH, and usually remain intrasellar even after a decade or more of clinical manifestations of GH overproduction. Using immunocytochemistry, in situ hybridization, and ultrastructural microscopy, GH-secreting pituitary tumors have been shown to be heterogeneous (2). They vary in cell size, granule size and density, and their content of PRL or TSH. Hyperprolactinemia occurs inapproximately one third of patients with GH-secreting adenomas. PRL is most frequently secreted from a mixed population of somatotroph and lactotroph tumor cells or an acidophilic stem cell tumor, but occasionally from a bihormonal somatomammotroph adenoma. © 1991 by The Endocrine Society.
