Diffusion-weighted MRI in bladder carcinoma: the differentiation between tumor recurrence and benign changes after resection.

Purpose: To investigate the efficacy of diffusion-weighted MRI (DWI) in differentiating recurrent tumor from chronic inflammation and fibrosis after cystectomy or transurethral resection of bladder cancer.
Methods: Eleven patients with suspected tumor recurrence underwent pelvic DWI and dynamic contrast-enhanced (DCE) MRI at 3 months to 7 years following bladder cancer resection. The diagnosis was histologically confirmed in all patients by transurethral or cystoscopic resection of 27 lesions within 2 weeks of MR examinations.
Results: The accuracies, sensitivities, specificities, and positive predict values of DWI (92.6%, 100%, 81.8%, and 88.9%) were higher than those of DCE MRI (59.3%, 81.3%, 27.3%, and 54.2%) for detecting recurrent tumors. Using receiver operating characteristic analysis, the accuracy of DWI was significantly higher than that of DCE MRI (P < 0.05). There was no significant difference between DWI diagnosis and histopathology (P > 0.05), whereas the difference between diagnosis of DCE MRI and histopathology was significant (P < 0.05). The normalized apparent diffusion coefficients of recurrent tumors (0.697 ± 0.219) were significantly (P < 0.05) lower than those of postoperative inflammation or fibrosis (1.019 ± 0.143).
Conclusions: DWI is superior to DCE MRI for differentiating recurrent bladder tumors from postoperative inflammation or fibrosis. DWI can be included in the follow-up MRI protocol after bladder cancer surgery.