Pheochromocytoma: physiopathologic implications and diagnostic evaluation.

Pheochromocytoma (PHEO) is a chromaffin cell tumor embryologically arising from the neural crest tissue. The dominant secretory products of PHEO are catecholamines: noradrenaline (norepinephrine), adrenaline (epinephrine), and to a lesser extent dopamine. In addition to catecholamines, PHEO cells also elaborate and release several neuropeptides and inflammatory cytokines which can exert intra-adrenal and extra-adrenal systemic effects and cause characteristic clinical syndromes. In a concise review we present the intra-adrenal and extra-adrenal pathophysiologic implications of PHEO and the nuclear medicine modalities that permit functional imaging of physiological processes and help localize these tumors. The specific pathways of synthesis, metabolism, and inactivation of catecholamines (of PHEOs and paragangliomas) can be used as means to develop suitable tracers for positron emission tomography (PET) ligands. In this review we focus on imaging with PET using [(18)F]-fluorodopamine, [(18)F]-fluorohydroxyphenylalanine, [(11)C]-epinephrine, or [(11)C]-hydroxyephedrine and examine how functional imaging can often complement traditional anatomical imaging modalities and other scintigraphic techniques.