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

Abstract Background 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 better identify adrenal adenomas than current recommendations. Methods 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. Results Using HU ≤ 10 to identify adenomas had a sensitivity of 47.6%, specificity of 93.3% (AUC = 0.71, p  60% for lesions exceeding 16HU, sensitivity increased to 93.4%, specificity was 93.3% and PPV 96.6%, and NPV improved to 85.7% (AUC = 0.96, p  Conclusions Criteria of initial threshold of HU ≤ 16 followed by APW>60% for lesions exceeding 16HU yielded improved sensitivity and specificity in identification of adrenal adenomas.