58 - Mechanisms of pituitary tumorigenesis

Summary

Introduction

The pituitary, a small bean-shaped gland at the base of the brain, maintains multiple homeostatic functions, including metabolism, growth, and reproduction. Most pituitary tumors are adenomas that develop in the adenohypophysis, the epithelial anterior lobe composed of six cell types that secrete polypeptide hormones.

Pituitary adenomas exhibit a wide range of hormonal and proliferative behaviors (1). They may be small, slowly growing and hormonally inactive, detected as radiographic “incidentalomas” or at post-mortem examination. When they produce hormones in excess, they cause mood disorders, sexual dysfunction, infertility, obesity and disfigurement, hypertension, diabetes mellitus, and accelerated heart disease. Untreated, hormone excess syndromes can be associated with diminished survival.

Some pituitary adenomas grow rapidly, producing symptoms of an intra-cranial mass, loss of normal anterior pituitary hormone production, and visual ield disturbances due to stretching of the overlying optic chiasm.hey can invade downward into paranasal sinuses, laterally into the cavernous sinuses (thereby disrupting co-ordinated eye movement) and upwards into the brain.hey can cause death by invasion of brain.

Early studies using X-chromosome inactivation proved that these adenomas are monoclonal neoplasms (2–5). Polyclonal results were attributed to contamination by normal tissue; the small adenomas associated with Cushing’s syndrome are particularly subject to this phenomenon (4,5).