Differentiation of Clear Cell Renal Cell Carcinoma From Other Subtypes and Fat-Poor Angiomyolipoma by Use of Quantitative Enhancement Measurement During Three-Phase MDCT

Objective: The purpose of this study was to retrospectively assess whether measurement of quantitative enhancement during three-phase MDCT can help differentiate clear cell renal cell carcinoma (RCC) from papillary RCC, chromophobe RCC, and fat-poor angiomyolipoma.

Materials and methods: During preoperative three-phase MDCT (unenhanced, corticomedullary, and early excretory phases), 563 lesions were identified in 552 consecutively registered patients. The lesions were assessed for attenuation in each phase, and the attenuation values were compared by t test. Cutoff analysis of enhancement values (percentage enhancement ratio, enhancement change, and absolute washout ratio) was performed to determine optimal thresholds for the four types of lesions.

Results: The mean attenuation of clear cell RCC was significantly greater than that of papillary RCC and chromophobe RCC in the corticomedullary phase (clear cell, 139.7 HU; papillary, 56.8 HU [p = 0.003]; chromophobe, 85.4 HU [p = 0.005]) and early excretory phase (clear cell, 86.9 HU; papillary, 73.4 HU [p = 0.03]; chromophobe, 68.2 HU [p = 0.02]). It was also significantly greater than that of fat-poor angiomyolipoma in the corticomedullary phase (139.7 vs 99.6 HU, p = 0.02). Establishment of threshold enhancement values helped to differentiate clear cell RCC from papillary RCC, chromophobe RCC, and fat-poor angiomyolipoma with the following accuracies: percentage enhancement ratio, 84.7% (399/471) for papillary RCC, 71.1% (325/457) for chromophobe RCC, and 81.9% (377/460) for fat-poor angiomyolipoma; enhancement change, 80.9% (381/471) for papillary RCC, 70.2% (321/457) for chromophobe RCC, and 80.6% (371/460) for fat-poor angiomyolipoma; absolute washout ratio, 88.5% (417/471) for papillary RCC, 74.1% (339/457) for chromophobe RCC, and 85.0% (391/460) for fat-poor angiomyolipoma.

Conclusion: Quantitative enhancement measurement may be useful for differentiating clear cell RCC from papillary RCC, chromophobe RCC, and fat-poor angiomyolipoma.