Accurate preoperative staging of urinary bladder carcinoma is the most important factor for the appropriate management and better prognosis as it depends on the clinical findings and stage at presentation [16,17,18]. Superficial tumors are treated with transurethral resection (TUR) with or without adjuvant intravesical chemotherapy or photodynamic therapy , whereas invasive tumors are treated with radical cystectomy, radiation therapy, chemotherapy, or a combination .
Cystoscopy and biopsy are considered as invasive techniques. Hence, the purpose of this study was to assess the degree of muscle invasion of the urinary bladder carcinoma by diffusion-weighted magnetic resonance imaging (DW-MRI) as well as to measure the correlation between ADC value and histologic grade of the urinary bladder cancer.
Several studies were done to assess value of DWI as being non-invasive imaging method in differentiating stage, grade, and cell type of the urinary bladder cancer [8, 13]. The feasibility of using DW-MR imaging for the detection of urinary bladder carcinoma has been reported by Matsuki et al. . They found that the sensitivity and positive predictive value of DW imaging were both 100% for detection of carcinoma. Similar findings were reported by El-Assmy et al. ; the sensitivity and positive predictive values of DW-MRI were 100% in terms of correctly detecting the bladder carcinomas on 43 patients.
In a study carried out by Abou-El-Ghar et al. , on 130 patients with hematuria, cystoscopy was considered as a standard reference. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of DW-MRI regarding the degree of muscle invasion of urinary bladder carcinoma were 98.5%, 93.3%, 100%, 92.3%, and 97% respectively. They found excellent agreement between the DW-MR imaging and the conventional cystoscopy. These results are similar to the present study, in which the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of DW-MRI were 100%, 80%, 90%, 100%, and 93%. The results of our study and previously published studies suggest a high reliability of DW-MR imaging for the diagnosis and proper staging of bladder carcinoma. In addition, DW-MR images can provide information regarding lesion size, number, and location to surgeons who perform conventional cystoscopy.
In a study done by Takeuchi et al. , they also found that the sensitivity, specificity, and accuracy for differentiating non-invasive from invasive urinary bladder tumors using T2WI images alone, and combined use of T2WI and DW images were 88%, 74%, 79%, and 88%, 100%, 96% respectively.
In a study done by Rima et al. , they reported that adding DWI to T2WI revealed higher accuracy (83%) than T2WI alone (75%). This agreed with our results and other researches [13, 23,24,25]. In the current study, we found that the overall agreement of DWI, T2WI, and both were 83.6%, 63.6%, and 65.5% respectively. In a study done by Abdel-Rahman et al. , they reported higher overall accuracy of diffusion-weighted images compared to T2WI in T staging of urinary bladder carcinoma.
Tekes et al. reported over staging of about 81% of bladder tumors when they assess the lesions using T2-weighted images alone, as tumors showed signal intensity like that of muscle layer on T2-weighted images. Also, the insufficient contrast between tumor and submucosa might cause low accuracy in T2WI .
Several authors had reported decreased ADC value among malignant lesions due to dense cellularity and large cellular size . El-Assmy et al. 2008 and Ceylan et al. 2010 found that the mean ADC values of patients who were diagnosed with a bladder tumor (1.05 ± 0.22 × 10−3 mm2/s) were significantly lower than the mean ADC values obtained from the normal bladder wall (1.830 ± 0.18 × 10−3 mm2/s) [21, 29]). In this study, the mean ADC of G1 tumors was significantly higher than that of G2 and G3 tumors. Meanwhile, there was an inverse relationship between the mean ADC values and the histological grade of the tumor. This was in accordance to results of different studies [20, 30, 31]. Based on our study and prior studies, the ADC values could predict the histologic grade of bladder cancer.
MRI examination including functional sequences proved to be valuable imaging modality in providing adequate information regarding morphological data and tumor cellularity . Multiparametric MRI imaging (mpMRI) is considered a promising imaging modality for assessment of tumor response to chemotherapy and radiotherapy . Multiparametric MRI imaging (mpMRI) included T2WIs, DWI, and dynamic contrast enhanced study. T1WIs are also needed to assess the presence of hemorrhage in the bladder and marrow signal alteration of the pelvic bones . Vesical Imaging-Reporting and Data System (VI-RADS) is a scoring system that aims to provide guidelines for detection of urinary bladder carcinoma and the degree of muscle invasion based on findings of multiparametric MRI imaging (mpMRI) .
In the present study, we found that DW-MRI has many advantages such as short acquisition time, non-invasive technique, and does not contain ionized radiation. Also, DW-MR imaging can be added to routine imaging protocols particularly in patients with renal impairment who cannot be examined using contrast study. DWI was performed without breath holding, thus allowing examination of severely ill, old, or obese patients who were unable to hold their breath for a long time. DW-MRI is a promising imaging tool. It could be accepted as an important marker of tumor cellularity.
Our study has few limitations; first, we included a larger number of advanced stage tumors. Second, images interpretation was done by one radiologist so interobserver correlation could not be assessed. Also, we did not use contrast in our study as we focused on the accuracy of diffusion imaging, to add DWI as a routine sequence in cases with urinary bladder lesions particularly in patients with impaired renal function.