Utility of the 10 Hounsfield unit threshold for identifying adrenal adenomas: Can we improve?

Current recommendations using Hounsfield units (HU) ≤ 10 to identify adrenal adenomas on unenhanced computed tomography (CT) miss 10–40% of benign adenomas. We sought to determine if changing HU threshold and adding absolute percent contrast washout (APW) criteria would identify adrenal adenomas better than current recommendations. Imaging characteristics were compared between patients with adenomas (n = 128) and those with non-adenomas (n = 54) after unilateral adrenalectomy. Sensitivity, specificity, positive and negative predictive values (PPV, NPV) were calculated. Using HU ≤ 10 to identify adenomas had a sensitivity of 47.6%, specificity of 93.3% (AUC = 0.71, p 60% for lesions exceeding 16 HU was optimal. Short Summary: Imaging characteristics on CT imaging can identify benign adrenal masses that do not need further imaging follow up. However, using the current cut-off of HU ≤ 10 only identifies half of benign adenomas. Applying HU ≤ 16 and examining absolute percent contrast washout for lesions exceeding this threshold improves sensitivity to 93.4% and specificity to 93.3% for identification of adrenal adenomas.