Utility of Quantitative MRI Metrics for Assessment of Stage and Grade of Urothelial Carcinoma of the Bladder: Preliminary Results

Abstract

The purpose of this study was to assess associations between quantitative MRI metrics and pathologic indicators of aggressiveness of urothelial carcinoma of the bladder. In this retrospective biinstitutional study, 37 patients (28 men and nine women; mean age, 73 ± 12 years) who underwent pelvic MRI including diffusion-weighted imaging (b values 0, 400, and 800 s/mm(2)) and T2-weighted imaging before transurethral resection or cystectomy for urothelial carcinoma of the bladder were identified. Tumor diameter (measured on T2-weighted imaging), normalized T2 signal intensity (to muscle; hereafter labeled normalized T2) and apparent diffusion coefficient (ADC) were measured for all tumors. Mann-Whitney test and receiver operating characteristic analyses were used to identify associations between these metrics and histopathologic tumor stage and grade. Thirty-seven tumors were assessed (mean size, 35 ± 23 mm; range 8-88 mm). At histopathologic analysis, 16 of 37 (43%) tumors were stage T2 or greater and 21 of 37 (57%) were stage T1 or lower, whereas 34 of 37 (92%) were high grade and three of 37 (8%) were low grade. High-stage (≥ T2) tumors showed greater tumor diameter, lower normalized T2, and lower ADC (p = 0.005-0.032) than low-stage (≤ T1) tumors. Tumor diameter and ADC were significant independent predictors of stage (p ≤ 0.043), with their combination giving an area-under the-curve (AUC) of 0.804. High-grade tumors showed significantly lower ADC (p = 0.023) but no significant difference in tumor diameter or normalized T2 (p = 0.201-0.559). AUC for differentiating low- and high-grade tumors was higher for ADC (0.902) than for tumor diameter (0.603) or normalized T2 (0.725). A combination of size and quantitative MRI metrics can potentially be used as markers of stage and grade of bladder cancer.