This is a PDF file of a peer-reviewed, preliminarily formatted and unedited paper that has been accepted for publication in Diagnostic and Interventional Radiology. Copyediting of the text and figures and proof review of the the paper will be finished before the paper is published in its final form. Please note that errors may be discovered which could affect the content of the paper during the production process. All legal disclaimers apply.' u n c o r r e c t e d p r o o fABSTRACT PURPOSE To explore the utility of four-phase computed tomography (CT) in distinguishing renal oncocytoma with central hypodense areas from clear cell renal cell carcinoma (ccRCC). METHODS Eighteen patients with oncocytoma and 63 patients with ccRCC presenting with central hypodense areas were included in this study. All patients underwent four-phase CT imaging including the excretory phases later than 20 min after contrast injection. Two blinded experienced radiologists visually reviewed the enhancement features of the central hypodense areas in the excretory phase images and selected the area demonstrating the greatest degree of enhancement of the tumor in the corticomedullary phase images. Regions of interest (ROIs) were placed in the same location in each of the three contrast-enhanced imaging phases. ROIs were also placed in the adjacent normal renal cortex for normalization. The ratio of lesion-to-cortex attenuation(L/C) for three contrast-enhanced imaging phases and absolute deenhancement were calculated. Receiver operating characteristic (ROC) curve was used to obtain the cutoff values. RESULTS Complete enhancement inversion of the central areas was observed in 12 oncocytomas (66.67%) and 16 ccRCCs (25.40%) (p=0.004). Complete enhancement inversion combined with L/C in the corticomedullary phase lower than 1.0 (p<0.001) or absolute deenhancement lower than 42.5 HU (p<0.001) provided 86.42% and 85.19% accuracy, 61.11% and 55.56% sensitivity, 93.65% and 93.65% specificity, 73.33% and 71.43% positive predictive value (PPV), and 89.39% and 88.06% negative predictive value (NPV), respectively, for the diagnosis of oncocytomas. Combined with complete enhancement inversion, L/C in the corticomedullary phase lower than 1.0 and absolute deenhancement lower than 42.5 HU provided 87.65%, 55.56%, 96.83%, 83.33%, and 88.41% of accuracy, sensitivity, specificity, PPV, and NPV, respectively, for the diagnosis of oncocytomas. CONCLUSION The combination of enhancement features of the central hypodense areas and the peripheral tumor parenchyma can help distinguish oncocytoma with central hypodense areas from ccRCC.