Can high-attenuation renal cysts be differentiated from renal cell carcinoma at unenhanced CT?

Purpose: To retrospectively determine if renal cell carcinoma can be differentiated from high-attenuation renal cysts at unenhanced computed tomography ( CT) based on Hounsfield unit measurements and heterogeneity. Materials and Methods: The Human Investigation Committee at our institution approved this study with waiver of informed consent. This study was compliant with the HIPAA. Fifty-four pathologically proved renal cell carcinomas in 54 patients ( 36 men and 18 women; average age, 53 years; range, 23-90 years) and 56 high-attenuation renal cysts in 51 patients ( 30 men and 21 women; average age, 63 years; range, 28-86 years) were retrospectively evaluated at unenhanced CT. Two independent readers reviewed randomized unenhanced CT images and obtained Hounsfield unit readings of each mass. A subjective determination of lesion heterogeneity was also performed by using a four-point scale ( 1: homogeneous, 2: mildly heterogeneous, 3: moderately heterogeneous, 4: markedly heterogeneous). Statistical analysis was performed by using Bland-Altman regression tree, classification and regression tree, and Shapiro-Wilk normality test. Results: The average attenuation of cysts for reader 1 was 53.4 HU ( range, 23-113 HU) and for reader 2 was 53.8 HU ( range, 21-108 HU). The average attenuation of neoplasms for reader 1 was 34.7 HU ( range, 21-60 HU) and for reader 2 was 38.4 HU ( range, 22-60 HU). For cyst heterogeneity, a score of 1 was given in 55 of 56 ( 98%) cysts for reader 1 and in 53 of 56 ( 95%) cysts for reader 2. For neoplasm heterogeneity, a score of 1 was given in 35 of 54 ( 65%) neoplasms for reader 1 and in 36 of 54 ( 67%) for reader 2. Given the distribution of cyst and tumor attenuation values and lesion heterogeneity, a homogeneous mass measuring 70 HU or greater at unenhanced CT has a greater than 99.9% chance of representing a high-attenuation renal cyst. Conclusion: The findings from this study may help differentiate high-attenuation renal cysts from renal cell carcinomas at unenhanced CT and may suggest the next appropriate imaging study for definitive characterization. (c) RSNA, 2007.