Incidental Adrenal Lesions: Accuracy of Characterization with Contrast-enhanced Washout Multidetector CT-10-minute Delayed Imaging Protocol Revisited in a Large Patient Cohort

Purpose: To reassess the accuracy of the 10-minute delayed scan to differentiate both lipid-rich and lipid-poor lesions in a large cohort of patients. Materials and Methods: This HIPAA-compliant retrospective study had institutional review board approval; the need for informed consent was waived. A multidetector computed tomography (CT) adrenal protocol (unenhanced, dynamic contrast material-enhanced, and 10-minute delayed CT) was used in 314 consecutive patients (201 women, 113 men; mean age, 63.6 years) for the period from January 2006 through February 2009. The mean adrenal attenuation during all three CT phases was measured by two readers, and the relative percentage washout (RPW) and absolute percentage washout (APW) values were calculated. APW and RPW receiver operating characteristic (ROC) analysis was performed to evaluate the strength of the tests. Results: There were 323 adrenal lesions (213 left, 110 right) consisting of 307 adenomas and 16 nonadenomas. The sensitivity, specificity, and accuracy for the RPW test at a washout threshold of 50% were 55.7%, 100%, and 57.9%, respectively; at 40% were 76.9%, 93.7%, and 77.7%; and at 35% were 81.4%, 93.7%, and 82.0%. The sensitivity, specificity, and accuracy for the APW test at a 60% threshold were 52.1%, 93.3%, and 54.0%, respectively; at 55% were 62.5%, 93.3%, and 64.0%; and at 50% were 71.3%, 80.0%, and 71.7%. Areas under the ROC curve were 0.85 (95% confidence interval: 0.75, 0.95) and 0.91 (95% confidence interval: 0.85, 0.97) for the APW and RPW tests, respectively, to detect adenomatous disease. Conclusion: The 10-minute delayed adrenal enhancement washout test has reduced sensitivity for the characterization of adrenal adenomas compared with results from prior studies. (C) RSNA, 2010