Evaluation of the Relative Enhancement Ratio and Morphologic Findings on Biphasic CT to Differentiate Clear Cell and Non-Clear Cell Renal Cell Carcinoma

Objective: To differentiate clear cell and non-clear cell renal cell carcinoma (RCC) using enhancement pattern, relative enhancement ratio and associated findings on CT scan. Methods: This retrospective study reviewed CT scan in the unenhanced, corticomedullary and nephrographic phase in clear cell and non-clear cell RCC. A total of 49 patients with surgically proven RCC, consisting of 42 clear cell RCCs, and 7 non-clear cell RCCs (6 papillary, 1 chromophobe). Two radiologists compared degree of enhancement, enhancement pattern, the presence or absence of calcification, perinephric change, pelvocalyceal involvement, neovascularization, venous invasion, lymphadenopathy and distant metastasis. Results: Both the attenuation value and degree of enhancement in the corticomedullary phase were higher in clear cell RCC than non-clear cell RCC. The relative enhancement ratio in the corticomedullary phase was significantly higher in clear cell than non-clear cell RCC. The cutoff value of the relative enhancement ratio higher than 1.629 was used to differentiate clear cell RCC from non-clear cell RCC and had the sensitivity, specificity, PPV, NPV and accuracy of 76.2%, 85.7%, 97%, 37.5% and 77.6%, respectively. Heterogeneous enhancement, perinephric change and neovascularization were found significantly more common in clear cell than non-clear cell RCC. Conclusion: The most useful parameter to differentiate clear cell from non-clear cell RCC is relative enhance- ment ratio in the corticomedullary phase.