Current views on imaging of adrenal tumors

Anatomical imaging modalities (such as computed tomography [CT] or magnetic resonance imaging [MRI]) and functional imaging modalities (that is, nuclear medicine) are used in the evaluation of adrenal glands. The use of CT (unenhanced, followed by contrast-enhanced) evaluation is the cornerstone of imaging of adrenal tumors. Attenuation values of less than 10 Hounsfield units at unenhanced CT are practically diagnostic for adenomas, while attenuation values of greater than 10 HU are not diagnostic of metastatic disease since non-metastatic disease is also a possibility. When lesions cannot be characterized adequately with CT, MRI evaluation (with T1 and T2-weighted sequences and chemical shift and fat-suppression refinements) is sought. Functional nuclear medicine imaging can be of utility in the evaluation of adrenal masses, more particularly for lesions not adequately characterized with CT and MRI. Nuclear medicine techniques are based on physiological and pathophysiological processes (cellular metabolism, tissue perfusion and local synthesis, uptake, storage of hormones and their receptors). Functional imaging aids initial preoperative staging, diagnostic evaluation of suspicious lesions, identification of metastatic or recurrent tumors, refining prognosis, and deciding on and predicting responses to therapy. [I-131]-6-iodomethyl norcholesterol scintigraphy can differentiate adenomas from carcinomas. Pheochromocytomas appear as areas of abnormal/increased [I-131]- and [I-123]-meta-iodobenzylguanidine uptake. Our experience has shown that [F-18]-fluorodopamine is an excellent agent for localizing adrenal and extra-adrenal pheochromocytomas.