Incidental adrenal lesions: Accuracy of quadriphasic contrast enhanced computed tomography in distinguishing adenomas from nonadenomas

Purpose

To evaluate the accuracy in distinguishing adrenal adenomas from nonadenomas by means of quadriphasic CT exam, including unenhanced (UE), arterial enhanced (AE), portal enhanced (PE) and 5-min delayed enhanced (DE) CT scans.

Methods

This retrospective study had institutional review board approval; the need for informed consent was waived. From September 2007 to September 2009, 104 adrenal masses were evaluated in 87 patients (49 M, 38 F, mean age 58.4 years) undergoing UE, AE (35-s delay), PE (80-s delay) and DE (5-min delay) CT scans. The mean adrenal attenuation during all imaging phases was measured by two readers. The accuracy values of absolute unenhanced attenuation (UE), absolute wash-out (AWO), relative percentage wash-out (RPWO) and percentage enhancement wash-out (PEW) were assessed by using receiver operator curves (ROC) analysis. The overall accuracy of the quadriphasic protocol and other triphasic protocols were evaluated. A value of p ≤ 0.05 was considered significant.

Results

The accuracy in characterizing adrenal lesions was 86.5% (90/104) for UE attenuation (≤10 HU threshold), 90.1% (82/91) for RPWO (≥30% threshold), 85.7% (78/91) for AWO (≥12 HU threshold) and 83.5% (76/91) for PEW (≥30% threshold), respectively. Quadriphasic CT (accuracy 97.1%, 101/104) performed better than triphasic CT including only AE scan (efficiency 90.0%, 94/104; p = 0.011) and triphasic CT including only PE scan (efficiency 96.1%, 100/104; p = 0.025).

Conclusion

Quadriphasic CT protocol including 5-min DE scan may be used to characterize incidentally detected adrenal masses. RPWO represented the best wash-out parameter for characterizing adrenal lesions.