Significance of ADC value for detection and characterization of urothelial carcinoma of upper urinary tract using diffusion-weighted MRI

To evaluate utility of diffusion-weighted magnetic resonance imaging (DWI) to detect and predict the histological characteristics of upper urinary tract urothelial carcinomas (UTUCs). We retrospectively evaluated 20 suspicious lesions from 19 patients. MRI study included conventional sequences and DWI with apparent diffusion coefficient (ADC) maps calculated between b = 0 and b = 1,000. ADC values were measured within two different regions of interest (ROI): a small identical ROI placed in the most restrictive part of the tumour and a larger ROI covering two-thirds of the mass surface. The mean ADC values of the tumours were compared with that of normal renal parenchyma using an unpaired Student's t test. Association between ADC values and histological features was tested using non-parametric tests. Overall, 18 tumours were confirmed histologically as UTUCs. DWI failed to detect two cases of UTUCs (one CIS and one small tumour of 5 mm). There was no statistically significant difference in ADC values measured with the small or large ROI (p = 0.134). The mean ADC value of UTUC was significantly lower than that of the normal renal parenchyma (p < 0.001). No statistical association was found between ADC values and pathological features (location, p = 0.35; grade, p = 0.98; muscle-invasive disease, p = 0.76 and locally advanced stage, p = 0.57). DWI may be interesting tool for detecting UTUCs regarding the difference of ADC values between the tumours and surrounding healthy tissues. In regard to low frequency of UTUCs, the association of ADC values and histological characteristics need further investigations in a large prospective multi-institutional study.