The use of CT and MR imaging has resulted in more frequent and incidental detectionof adrenal masses. More recent research has been focused on different approaches tocharacterizing adrenal masses on cross-sectional images, including assessing lesionsize, describing morphologic criteria, measuring attenuation or signal intensity,calculating the percentage loss of enhancement, and determining the lipid content.However, there are no literature reports of comparisons between the attenuation andpercentage loss of enhancement values for adrenocortical carcinomas andpheochromocytomas as those for the more frequently encountered adrenal adenomasand adrenal metastases.Two main CT features used to distinguish adenomas from nonadenomas have beenidentified: the intracellular lipid content and the enhancement loss in adrenal masses.Adenomas often contain abundant intracytoplasmatic fat and thus have lowattenuation on nonenhanced CT scans and signal loss on opposed phase MR images.Conversely, nonadenomas contain little or no intracytoplasmatic fat and thus havehigher attenuation at nonenhanced CT and no signal loss at opposed phase MRimaging. Korobkin et al, 1996 observed that the intratumoral lipid content of resectedadrenal adenomas correlated with lower attenuation at nonenhanced CT. Although anattenuation value of less than 10 HU at nonenhanced CT is considered sufficient forcharacterizing an adrenal mass as an adenoma, it has been estimated that up to 30% ofadenomas do not contain large amounts of lipid and may remain indeterminate andindistinguishable from nonadenomas on nonenhanced CT scans or chemical shift MRimages.