Role of MRI in Assessment of the Urinary Bladder Wall Post Transurethral Tumor Resection

Urinary bladder carcinoma is the second most common tumour of the urinary tract and 70% of such carcinomas are non-muscle-invasive (superficial) at presentation. Transurethral resection (TUR) is the standard treatment; however, recurrence of the tumour is not uncommon so such patients require long-term close supervision. Staging is based on TNM system. Ta tumors are treated with transurethral resection of bladder tumor (TUR-BT). T1 and carcinoma in situ (Tis) tumors have risk of progression and intravesical immunotherapy with Bacillus-Calmette-Guerin (BCG) instillations is used to obtain local control and organ preservation. Invasive bladder cancer (MIBC) is an aggressive disease and standard treatment is radical cystectomy (RC), accompanied by pelvic lymph node dissection (PLND). In addition to radical surgery, neoadjuvant chemotherapy (NAC) has been demonstrated to increase overall survival in MIBC and is recommended by consensus guidelines. Compared to contrast enhanced CT, MRI has better soft tissue contrast which may improve local tumor evaluation. Surveillance strategies for urinary bladder carcinoma recurrence have historically relied on cystoscopy, but this procedure has drawbacks, including its high cost, invasiveness and the fact that it may lead to iatrogenic bladder injury and urinary sepsis. In addition, it cannot diagnose upper tract tumours. The presence of a radiological method that could differentiate between benign and malignant lesions of the bladder would avoid the need for invasive cystoscopy, provided that upper tract tumours were excluded. Diffusion-weighted (DW) MRI is a non-invasive technique measuring the microscopic mobility of water molecules in the tissues without contrast administration. It provides information on perfusion and diffusion simultaneously in any organ, so it can be used to differentiate normal and abnormal structures of tissues, and it might help in the characterization of various abnormalities. During follow-up of patients after trans-urethral resection (TUR), it is difficult to distinguish residual cancer from fibrotic and inflammatory changes secondary to TUR and intravesical chemotherapy, both of which manifest as bladder wall thickening on T2-weighted MRI.