Differentiation of Benign From Metastatic Adrenal Masses in Patients With Renal Cell Carcinoma on Contrast-Enhanced CT

OBJECTIVE: The purpose of this article was to determine whether imaging features on contrast-enhanced CT can differentiate benign from metastatic adrenal masses in patients with renal cell carcinoma (RCC). MATERIALS AND METHODS: Between January 2008 and January 2014, 135 patients with untreated RCC were found to have 163 adrenal masses (102 benign and 61 metastatic) on contrast-enhanced CT including the corticomedullary phase (66 benign and 42 metastatic) or nephrographic phase (56 benign and 33 metastatic) or both. Imaging features of renal and adrenal masses were recorded, including T and N staging components of renal masses, internal texture, CT attenuation values, and attenuation differences between renal and adrenal masses. Logistic regression diagnostic models to differentiate benign from metastatic adrenal mass were constructed using independently significant imaging parameters in the respective corticomedullary and nephrographic phases (corticomedullary phase model and nephrographic phase model). Diagnostic performance of the models was evaluated by ROC analysis. RESULTS: Statistically significant variables for the models were regional lymphadenopathy, perirenal or renal sinus fat invasion (corticomedullary phase model only), adrenal mass size, CT attenuation value of adrenal mass, and absolute value of attenuation difference between renal and adrenal masses. Both models had excellent diagnostic performance; the AUC and optimal sensitivity and specificity for the diagnosis of metastasis were 0.991, 100%, and 92.4%, respectively, in the corticomedullary phase model and 0.947, 81.8%, and 96.4%, respectively, in the nephrographic phase model. CONCLUSION: Differentiation between benign and metastatic adrenal masses in patients with RCC can be achieved accurately by combining multiple imaging features on contrast-enhanced CT.