Apoplexy of pituitary adenomas: the perfect storm.

Abstract

Pituitary adenomas occasionally undergo infarction, apoplexy, which often destroys much of the tumor. It is well known that apoplexy can be precipitated by several acute factors, including cardiac surgery, other types of surgery, trauma, insulin infusion, and stimulation with administration of hypothalamic releasing factors. The prior focus on mechanisms underlying pituitary apoplexy has been on these acute events. Less attention has been given to the endogenous features of pituitary tumors that make them susceptible to spontaneous infarction, despite that most pituitary apoplexy occurs in the absence of a recognized precipitating event. The authors examine intrinsic features of pituitary adenomas that render them vulnerable to apoplexy-features such as high metabolic demand, paucity of angiogenesis, and sparse vascularity, qualities that have previously not been linked with apoplexy-and argue that it is these features of adenomas that underlie their susceptibility to spontaneous infarction. The sensitivity of freshly cultured pituitary adenomas to hypoglycemia is assessed. Adenomas have high metabolic demand, limited angiogenesis, and reduced vessel density compared with the normal gland. Pituitary adenoma cells do not survive in the presence of reduced or absent concentrations of glucose. The authors propose that the frequent ischemic infarction of pituitary adenomas is the product of intrinsic features of these tumors. These endogenous qualities create a tenuous balance between high metabolic demand and marginal tissue perfusion. Thus, the tumor is vulnerable to spontaneous infarction or to acute ischemia by any event that acutely alters the balance between tumor perfusion and tumor metabolism, events such as acute systemic hypotension, abruptly decreased supply of nutrients, hypoglycemia with insulin administration, or increase in the tumor's metabolic demand due to administration of hypothalamic releasing factors. It may be possible to take advantage of these intrinsic features of pituitary adenomas by using aspects of this vulnerability for development of new approaches for treatment.