Preoperative T Staging of Urinary Bladder Cancer: Does Diffusion-Weighted MRI Have Supplementary Value?

OBJECTIVE. The objective of our study was to evaluate whether diffusion-weighted MRI has supplementary value in the preoperative T staging of urinary bladder cancer. MATERIALS AND METHODS. Nineteen consecutive patients (18 men and one woman; age range, 55-83 years; mean, 71 years) known to have or suspected of having urinary bladder cancer underwent MRI at our institution. Urinary bladder cancer was pathologically proven in 18 patients. The pathologic stages were T1 in 14 patients, T2 in two, T3 in one, and T4 in one. Three separate MR image sets were retrospectively reviewed by two independent radiologists: unenhanced T1-weighted images (TR/TE, 607/10) and T2-weighted images (TR eff/TE eff, 4,415/100); unenhanced T1-weighted, T2-weighted, and gadolinium-enhanced images (TR/TE, 10/4.2); and unenhanced T1-weighted, T2-weighted, and diffusion-weighted images (TR (eff)/TEeff, 2,191/69; b factor, 1,000 s/mm(2)). The radiologists, who were blinded to the pathology findings, assigned T stages and confidence levels for tumors of stage T2 or greater. We used pathologic stages documented in the official pathologic reports as the standard of reference. Observer performance was tested using Spearman's rank correlation, the McNemar test, and receiver operating characteristic (ROC) curve analysis. RESULTS. The correlation between the radiologic and pathologic stages was greater with the diffusion sequence (rho = 0.66) than with the unenhanced (0.62) or gadolinium-enhanced (0.62) sequence (p = 0.34). The sensitivity, specificity, accuracy, and area under the ROC curve for tumors of stage T2 or greater were 80%, 79%, 79%, and 0.71 for the unenhanced sequence; 80%, 79%, 79%, and 0.77 for the gadolinium sequence; and 40%, 93%, 79%, and 0.56 for the diffusion-weighted sequence, respectively (p > 0.05). CONCLUSION. Our results suggest that diffusion-weighted MRI might have high specificity for the detection of invasive urinary bladder tumors. Patients with suspected urinary bladder carcinomas may well be evaluated by MRI including diffusion-weighted imaging for better preoperative T staging.