Urinary collecting system invasion on multiphasic CT in renal cell carcinomas: prevalence, characteristics, and clinical significance.

The aim of this study was to determine the prevalence of collecting system invasion (CSI) on multiphasic CT, validate the pathological findings, and investigate the relationship between CSI and clinical outcomes in patients with renal cell carcinomas (RCC). Patients pathologically diagnosed with RCC between January 2008 and December 2017 were retrospectively enrolled in this study. They were divided into two groups according to the presence of CSI on multiphasic CT images. Patients’ clinical characteristics, radiological findings, and overall survival (OS) and recurrence-free survival (RFS) rates were analyzed and compared between the groups. In addition, the correlation of radiological findings with pathological findings was investigated. Among the included 347 kidneys of 340 patients, CSI was observed in 11 kidneys (3%; 95% confidence interval, 1.3–5.0%). In all the 11 kidneys, the tumors were pathologically diagnosed as clear cell RCC, and in one kidney, the tumor also had sarcomatoid features. When pathological CSI served as the standard of reference, the sensitivity, specificity, and accuracy of CSI on CT were 50%, 99.7%, and 97.1%, respectively. The OS and RFS rates were not significantly different between patients with CSI on CT and those without CSI. This study found that the prevalence of RCC-related CSI was 3%. Because of the low prevalence, we cannot exclude the possibility that CSI on CT would be associated with the OS and RFS. Further studies are needed to determine whether CSI on CT can be an independent prognostic factor for survival in patients with RCC.