Urothelial cancer is the most common malignancy of the urinary tract. Most patients present with hematuria and undergo initial imaging with CT and/or ultrasound for the assessment of potential etiologies of this symptom. A cystoscopy and biopsy are necessary to confirm the diagnosis of bladder cancer. The potential role of MRI is to triage patients to different forms of treatment according to the cancer’s stage. Most tumors confined to the bladder mucosa (non-invasive papillary carcinoma or carcinoma in situ) or submucosa (pathology stage T1), but about a quarter of patients present with tumors invading the muscular layer of the bladder and beyond (pathology stage ≥ T2). Prognosis is heavily dependent on the pathologic grade and stage of the primary tumor and, in particular, involvement of the regional pelvic lymph nodes. While low-grade non-muscle-invasive cancers have the most favorable oncologic outcomes and are typically managed conservatively, radical cystectomy is the standard treatment for muscle-invasive tumors and high-grade non-muscle-invasive lesions that are resistant to intravesical treatments. Thus, many patients undergoing radical cystectomy will have received either prior intravesical Bacillus Calmette-Guérin (BCG) for high-risk non-muscle-invasive disease or systemic neoadjuvant chemotherapy, which is used as part of a multimodality approach for muscle-invasive disease. Because the clinical behavior patterns and management strategies for high-risk and low-risk bladder cancers differ acutely, accurate staging of bladder cancer is of paramount importance.

In a small but important minority of cases, urothelial cancers can involve the “upper tracts”, which include the pelvicalyceal systems and ureters bilaterally. Upper tract urothelial involvement can occur in isolation, synchronously or metachronously with primary bladder tumors. They often present as flat or polypoid lesions that can be visualized as filling defects after IV contrast urinary excretion on MRI – the principle of imaging in MR Urography.

The management of urothelial cancers is based on observations from the cystoscopic evaluation, pathologic findings and imaging features. Serum and urine cytology and molecular marker assays for bladder cancer screening, diagnosis and staging have so far proven unsatisfactory for widespread use in routine clinical practice. Biopsies, while critical in diagnosis and staging, cannot provide definitive information on certain factors important for staging, such as extravesical tumor extension and the presence of nodal or distant metastases. Instead, several imaging modalities have traditionally been used to assess these factors. Fluoroscopic techniques (e.g. antegrade or retrograde cystography) have been largely superseded by CT and MRI. More recently, positron emission tomography (PET), alone or in combination with CT, has also been used in an attempt to provide insight into tumor metabolism in addition to anatomical delineation. All of these techniques have theoretical advantages and limitations, and none of them has demonstrated absolute supremacy over the others in terms of accuracy.

In this session we will focus on the role of MRI in urothelial cancers. Due to its superb soft-tissue resolution and exquisite depiction of the anatomical detail, MRI is currently the modality of choice for the evaluation of cancer involving pelvic structures such as the prostate, female reproductive organs and rectum. It is interesting that our ability to accurately stage bladder cancer has failed to mirror the improvements in the imaging assessment of other pelvic pathologies and the unquestionable technological advances in imaging. This suggests that the main barriers to be overcome may be related not to technical issues, but rather to the inherent characteristics of bladder cancer patients and their disease. There are several factors that account for the reported modest staging accuracy of imaging for the assessment of bladder cancer. The most important one is the difficulty of interpreting imaging examinations in patients who have had prior intravesical treatment with BCG. Meta-analyses of randomized clinical trials have found that, as compared to transurethral resection alone, adjuvant instillation of intravesical BCG after transurethral resection reduces recurrence rates in patients with high-risk non-muscle-invasive bladder cancer. Multiple BCG instillations are typically given, and maintenance schedules that include up to 30 instillations over 3 years have been recommended. Unfortunately, staging accuracy is negatively affected by prior BCG administration. Another important factor is the difficulty of distinguishing post-resection changes in the bladder wall and perivesical soft tissue from tumor infiltration. This difficulty may be responsible for overstaging in about a third of patients with MRI.