High-grade bladder cancer: Association of the apparent diffusion coefficient with metastatic disease: Preliminary results

Purpose: To assess the utility of apparent diffusion coefficient (ADC) values obtained from diffusion-weighted imaging (DWI) in distinguishing high-grade bladder cancer with and without metastatic disease. Materials and Methods: Seventeen patients with histologically confirmed high-grade bladder cancer who underwent pelvic magnetic resonance imaging (MRI) at 1.5T including DWI using b-values of 0, 400, and 800 sec/mm² were assessed. Histologic findings and follow-up imaging were used to establish the reference standard in terms of metastatic disease. Two radiologists independently recorded ADC of all lesions following a training session, with their results averaged. Mann-Whitney U-test, receiver operating characteristic (ROC) curve analysis and intraclass correlation coefficient (ICC) were used for data analysis. Results: Metastatic disease was characterized as present or absent in eight and nine patients, respectively. ADC was significantly lower among cases with metastatic disease than among cases without metastatic disease, both within the entire cohort (1.07 ± 0.18 × 10^-3 mm²/s vs. 1.45 ± 0.22 × 10^-3 mm²/s; P = 0.002) and within the subset of patients with muscle-invasive tumor (1.06 ± 0.19 × 10^-3 mm²/s vs. 1.45 ± 0.23 × 10^-3 mm²/s; P = 0.017). Area under the ROC curve for identifying metastatic disease using ADC was 0.944, with optimal threshold of 1.21 × 10^-3 mm²/s, which was associated with a sensitivity of 87.5%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 90.0%. Interreader agreement for ADC was excellent (ICC = 0.91). Conclusion: In this preliminary study, ADC was significantly different between cases of high-grade urothelial carcinoma of the bladder with and without metastatic disease. These results may have value in assessing the metastatic potential of patients with localized high-grade tumors of the bladder.