Preoperative staging of urinary bladder carcinomas using TNM system is crucial in the management of bladder cancer which is determined mainly by stage and grade of tumor at diagnosis [1, 12].
TURBT is the current standard for determining the presence or absence of muscle invasion, provides an estimate of pathologic subtype and grade, and can be completely curative in some times if the entire tumor is resected [12, 13]. However, TURBT has been found to underestimate T stage in up to 40% of patients, is inaccurate at determining tumor grade in up to 15% of patients, and frequently needs to be repeated . Furthermore, adherence to guidelines recommending repeat TURBT varies widely between urologists .
Improving MRI technology had led to introduction of mp-MRI (including high-resolution T2 WI, DW MRI, and DCE MRI) providing both anatomic and functional evaluation of the local staging and grading of bladder cancer with relatively high accuracy .
The overall T2 staging diagnostic accuracy in the current study was 72.3%, which is higher compared to previous similar studies. In the study conducted by Takeuchi et al.  on 52 patients with bladder tumor using 1.5-T MRI, they found that the overall diagnostic accuracy of T2WI in local T staging of bladder tumor was 67%. A study by Afifi et al.  using 1.5-T magnet, conducted on 50 patients with bladder cancer, showed T2 staging diagnostic accuracy of 52%. Another interesting study by Abou-El-Ghar et al.  using 1.5-T MRI conducted on larger number of patients (130 patients) showed T2 staging diagnostic accuracy of 39.6%. The improved diagnostic accuracy of our study may be attributed to the use of 3-T MRI, as the most of the previous studies were done on 1.5-T magnet.
The current study revealed T2 diagnostic accuracy of 71% in differentiating superficial from invasive tumors. This was better than Takeuchi et al.  who reported a diagnostic accuracy of 79% and Barsoum et al.  who reported a diagnostic accuracy of 88%.
Our study revealed T2 diagnostic accuracies of 85.2% in differentiating organ-confined from non-organ-confined tumors. This was similar to Takeuchi et al.  who reported a diagnostic accuracy of 85% and less than Barsoum et al.  who reported a diagnostic accuracy of 94%.
In the current study, overall staging accuracy of DCE-MRI was 87% and overstaging was detected in 13% of patients. Our results were better than those reported by Afifi et al.  who reported accuracy of (74%) and overstaging of about 26%. In their study, Gupta et al.  detected less staging accuracy of DCE MRI (73.3%) and more overstaging (20%) compared to our results. Also, Takeuchi et al.  reported accuracies between 75 and 92% which is comparable to our results.
To our knowledge, the accuracy of dynamic contrast-enhanced MR images for differentiating between T1 or lower tumors and T2 or higher tumors has been reported to be 75–92% [14, 18, 19], and it was reported to be 75–92% for differentiating between T2 or lower tumors and T3 or higher tumors. The overall accuracy for diagnosing tumor stage has been reported to be 52–93% [14, 18].
Our study revealed a significant statistical correlation (P < 0.001) between grading, time-intensity curves, and corresponding histopathological grades. Grade 1 curve only identified in low-grade tumors (3.7%), grade 3 curve mostly identified in high-grade tumors (75.9%), while grade 2 curve were more identified in low-grade (72.7%) than in high-grade carcinomas (27.3%). This was in agreement with Afifi et al.  and Gupta et al.  who showed significant correlation between time-intensity curves and tumors grading.
Quantitative analysis of the ADC values potentially reflects the histological grades of urothelial tumors. To our knowledge, DWI was superior to DCE-MRI and T2W-MRI in detection and local staging of urinary bladder cancers [13, 20].
The overall staging accuracy of DW-MRI in current study was 92.6% and overstaging was detected in 7.4% of patients. Our results are better than results reported by Gupta et al.  who detected less DWI staging accuracy (76.7%) and more overstaging (16.7%) and also Afifi et al.  who showed an overall staging accuracy of DW-MRI of 82% and overstaging in 18% of patients.
Our study revealed DWI diagnostic accuracies of 96.3% in differentiating both superficial from muscle-invasive and organ-confined from non-organ confined tumors. These results were higher than El-Assmy et al.  results who found the DWI staging accuracies of 63.6% and 69.6% in differentiating superficial from muscle-invasive and organ-confined from non-organ confined tumors, respectively. On other hand, our results were similar to Barsoum et al.  results who reported the accuracies of 96% and 98%, respectively.
In the current study, the correlation between the radiologic and pathologic stages was greater with the DWI (q = 0.766) than with the T2WI (0.527) or gadolinium-enhanced (0.758) which was in agreement with results reported by Watanabe et al.  and Gupta et al. . Similar results also were detected in Afifi et al.  study who also found greater correlation between the radiologic and pathologic stages with the diffusion sequence (q = 0.679) than with the T2W (0.274) or gadolinium-enhanced (0.566).
By comparing multiparametric acquisition protocols, we found that the combination of T2-weighted, DWI, and DCE-MRI was most accurate for staging. Overall staging accuracy of mp-MRI in current study was 94.5% and overstaging was detected only in 5.9% of patients. These results were better than study of Afifi et al.  who reported mp-MRI overall staging accuracy of 88% and overstaging was detected only in 12% of their patients. Takeuchi et al.  also stated that theT2-WI diagnostic accuracy for the T stage was 67%, increased to be 88% for T2WI plus DWI, 79% for T2 WI plus contrast-enhanced images, and 92% for all three image types reaching the maximum accuracy using the combined multi-parametric assessment.
Our study revealed mp-MRI diagnostic accuracy of 94.4% in differentiating superficial from invasive tumors. This was better than van der Pol et al.  who reported diagnostic accuracy of 84 to 86% and Afifi et al.  who reported diagnostic accuracy of 88%.
Our study revealed mp-MRI diagnostic accuracy of 98.1% in differentiating organ-confined from non-organ-confined tumors. This was better than van der Pol et al.  who reported diagnostic accuracy of 81 to 83% and Afifi et al.  who reported diagnostic accuracy of 88%.
In this study, we found that the mean ADC value of the detected malignant bladder lesions was 0.813 ± 0.24 × 10−3 mm2/s, which is significantly lower than that of urine (mean 2.71 ± 0.35) and that of normal bladder wall (mean 1.56 ± 0.41). This was similar to Afifi et al.  who reported mean ADC value in bladder cancers of 0.87 ± 0.26 × 10−3 mm2/s, significantly lower than that of urine (mean 2.90 ± 0.25) and that of normal bladder wall (mean 1.57 ± 0.17). Our results also agreed with Kobayashi et al.  study.
In current study, we detected a cutoff ADC value of < 1.36 × 10−3 mm2/s differentiating bladder carcinomas from normal bladder wall and a cutoff ADC value of 0.941 × 10−3 mm2/s differentiating high-grade from low-grade carcinomas. Similar results were detected by Afifi et al.  who found that a cutoff ADC value of < 1.36 × 10−3 mm2/s differentiating bladder carcinomas from normal bladder wall and a cutoff ADC value of < 1.012 × 10−3 mm2/s differentiating high-grade from low-grade carcinomas.
On the other hand, Kobayashi et al.  stated a cutoff ADC value of 0.86 × 10−3 × 10−3 mm2/s differentiating aggressive from low-grade disease which is lower than cutoff value detected in our study. Avcu et al.  stated a cutoff ADC value 1.545 × 10−3 mm2/s differentiating malignant and benign bladder wall pathologies and a cutoff ADC value 1.135× × 10−3 mm2/s differentiating high and low-grade carcinomas which is higher than our results.
We detected inverse correlation between bladder carcinomas ADC values and T stages, as ADC values were significantly lower in high stage tumors P T2 (mean 0.79 ± 0.28 × 10−3 mm2/s) than the superficial tumorsT1 (mean 1.04 ± 0.26 × 10−3 mm2/s). This was similar to Afifi et al. , who reported that the ADC values were significantly lower in high stage tumors P T2 (mean 0.69 ± 0.13 × 10−3 mm2/s) than the superficial tumors T1 (mean 0.97 ± 0.26 × 10−3 mm2/s). Similar to our results, Kobayashi et al. found that patients with higher T stages exhibited significantly lower ADC values (P < 0.001).
Our study had a number of limitations; the distribution of T stages was uneven, with a large number of T2 and T3 and a small number of T1 and T4 tumors; therefore, larger studies are warranted to more fully define the role of mpMRI in T staging of bladder tumors. Limitations of the current study included increased cost, time consumed by the technique especially including the cost of the contrast, and some patients were less cooperative with motion artifacts as the study mandates full UB. Finally, the radiologic-pathologic correlation was not perfect because the cut surfaces on surgical specimens were not always completely identical to those seen on MR images.
It is expected that utilization of mp-MRI for bladder cancer local T staging will increase as awareness of its accuracy in the urology community improves. Several recent meta-analyses assessing the topic of local staging of bladder cancer with mp-MRI confirm an increase in the potential benefits of performing mp-MRI .