Preoperative T categorization and prediction of histopathologic grading of urothelial carcinoma in renal pelvis using diffusion-weighted MRI

OBJECTIVE. The purpose of our study was to evaluate the utility of diffusion-weighted MRI (DWI) for preoperative T categorization and prediction of the histopathologic grade of renal pelvic cancer. MATERIALS AND METHODS. We retrospectively evaluated 40 renal pelvic cancers from 40 patients. The MRI included T2-weighted single-shot fast spin-echo, DWI, and contrast-enhanced imaging. Two radiologists independently reviewed three image sets (T2- weighted images alone, T2-weighted plus DWI, and T2-weighted plus contrast-enhanced images) regarding tumor detection and the discrimination of locally advanced tumors. The diagnostic performance among the three image sets were compared using Cochrane test followed by McNemar tests. The apparent diffusion coefficients between two histopathologic grades were compared using the Mann-Whitney U test. RESULTS. T2-weighted imaging plus DWI enabled a high detection rate (98%, 39/40) without significant differences. For the diagnosis of T3 or higher categories, the accuracies were relatively low in all three image sets (70% each for T2-weighted imaging plus DWI and T2-weighted imaging plus contrast-enhanced imaging and 58% for T2-weighted imaging alone, p > 0.05), with sensitivities of 58%, 65%, and 54%, respectively. For discriminating tumors with macroscopic renal invasion from those with microscopic renal invasion or less, T2-weighted imaging plus DWI (93%) was significantly more accurate than T2-weighted imaging alone (75%) (p = 0.016). The mean apparent diffusion coefficient of the high-grade tumors was significantly lower than that of the low-grade tumors (p < 0.01). CONCLUSION. DWI could be used for preoperative T categorization and prediction of the histopathologic grade of renal pelvic cancer without contrast material.