A Critical Analysis of Computed Tomography Washout in Lipid-Poor Adrenal Incidentalomas.

BACKGROUND Contrast-enhanced computed tomography (CT) with washout has emerged as an option to distinguish lipid-poor adenomas from non-adenomas. OBJECTIVE The aim of this study was to assess the utility of CT washout in characterizing indeterminate lipid-poor adrenal incidentalomas. METHODS From an Institutional Review Board-approved database, patients with adrenal incidentalomas who had adrenal protocol CT scans with a 15-min washout between 2003 and 2019 were identified. Non-contrast CT attenuation and washout patterns of different tumor types were compared. RESULTS Overall, 156 patients with 175 adrenal lesions were included. Average tumor size was 3.0 cm, non-contrast CT density was 24.7 Hounsfield units (HU), and absolute washout was 52.6%. In 102 lesions (58.3%), CT washout was ≥ 60%; 94 (92.2%) of these were benign adrenocortical adenomas, 7 (6.9%) were pheochromocytomas, and 1 (0.9%) was an adrenal hematoma. Furthermore, in 73 tumors (41.7%), CT washout was   60% absolute CT washout for detecting an adrenal adenoma was 67.6%, 77.8%, 92.2%, 38.4%, and 69.7%, respectively. CONCLUSION CT washout should be incorporated into the management algorithm of indeterminate adrenal incidentalomas with a high non-contrast CT attenuation to 'rule-in' benign tumors. For small tumors with mild elevation of plasma metanephrines, it should be kept in mind that adenomas and pheochromocytomas may have similar imaging and washout characteristics.