Evaluation of Adrenal Metastases from Renal Cell Carcinoma and Hepatocellular Carcinoma: Use of Delayed Contrast-enhanced CT

Purpose: To retrospectively compare absolute and relative washout of adrenal metastases in patients with renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC) to that of adrenal adenoma. Materials and Methods: Between November 1994 and August 2011, in this institutional review board-approved study (with waiver of informed consent), 16 patients with 19 adrenal metastases (16 in 13 RCC patients, three in three HCC patients) and 20 patients with 21 adrenal adenomas (16 in 15 RCC patients, five in five HCC patients) underwent dedicated adrenal protocol consisting of unenhanced, 1-minute contrast material-enhanced, and 15-minute delayed contrast-enhanced computed tomography (CT). The attenuation values and percentage enhancement washout, including absolute percentage washout (APW) and relative percentage washout (RPW), were calculated. If available, histologic findings and the change in the size of adrenal lesions were assessed. Statistical analyses were performed by using generalized estimating equation and coefficient of variation. Results: The mean APW of the metastases (observer 1, 67% +/- 11 [standard deviation]; observer 2, 63% +/- 12) was not significantly different from that of adenomas (observer 1, 73% +/- 9; observer 2, 72% +/- 12) for observer 1 (P = .143) and was significantly different for observer 2 (P = .029). The mean RPW of the metastases (observer 1, 46% +/- 11; observer 2, 43% +/- 12) was significantly lower than that of adenomas (observer 1, 62% +/- 19; observer 2, 60% +/- 17) (all P < .001 for each observer). With a threshold of 60% for APW or 40% for RPW, 95% (18 of 19) and 89% (17 of 19), respectively, of the metastases were falsely diagnosed as lipid-poor adenomas by each observer. All nine metastases that were followed up at CT had a substantial growth in size. Conclusion: In patients with RCC and HCC who undergo dedicated adrenal CT imaging for known adrenal lesions, the percentage enhancement washout of adrenal metastases is similar to that of lipid-poor adrenal adenomas. Careful imaging follow-up or pathologic tissue confirmation is needed. (C)RSNA, 2012 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120110/-/DC1