CT Time-attenuation Washout Curves of Adrenal Adenomas and Nonadenomas

Objective: The purpose of this study was to analyze the CT contrast enhancement washout curves of adrenal masses and to determine the earliest time after initial enhancement that differentiation of adenomas from nonadenomas is possible.

Materials And Methods: Contrast enhancement washout curves were generated after delayed contrast-enhanced CT scans of 52 adrenal adenomas and 24 nonadenomas. The optimal threshold value and corresponding sensitivity and specificity for the diagnosis of adenoma were determined according to attenuation values. Also, we calculated the percentage and relative percentage of enhancement washout at time delays from 5 to 45 min after initial enhancement.

Results: The mean percentage of enhancement washout for adrenal adenomas was 51% at 5 min and 70% at 15 min, compared with 8% and 20%, respectively, for nonadenomas. The sensitivity and specificity for the diagnosis of adenoma were both 96% at a threshold attenuation value of 37 H on the 15-min delayed enhanced scan.

Conclusion: On CT, adrenal adenomas show a much earlier and more rapid washout of contrast enhancement than do nonadenomas. Adenomas and nonadenomas can be differentiated by attenuation values or the percentage or relative percentage of washout as early as 5-15 min after enhancement.