What findings on CT help distinguish between benign and malignant tumors?
Adrenal nodule size and imaging characteristics are the two major predictors of malignancy. Adrenocortical carcinoma (ACC) accounts for only 2% of lesions < 4 cm but up to 25% of those > 6 cm. Benign adenomas are typically < 4 cm, are homogeneous with smooth borders, have a high lipid content (low attenuation—< 10 Hounsfield units [HU] on noncontrast images), and rapid contrast washout (> 50% washout) on delayed images 10 minutes after the contrast bolus. Malignant tumors are typically > 6 cm, heterogeneous with irregular borders, and have increased noncontrast attenuation (> 10 HU) and slower contrast washout.