Synergy of PET and MR imaging in the local and regional staging of bladder cancer

The prognosis and optimal management of bladder cancer are closely dependent on accurate clinical staging. Traditional staging has relied on transurethral resection for T-staging in combination with cross-sectional imaging for N and M-staging. Computed tomography (CT) is the most accessible and common cross-sectional imaging modality to assess for local and distant spread of disease. However, CT alone lacks the contrast resolution to distinguish between non-muscle-invasive and muscle-invasive disease and has known difficulty distinguishing metastatic from normal lymph nodes (LNs). Magnetic resonance imaging (MRI) and positron emission tomography (PET) have been increasingly used in the workup of bladder cancer to address the shortcomings of CT imaging. MRI using the multiparametric combination of T2-weighted, dynamic contrast-enhanced, and diffusion-weighted imaging can more clearly delineate the extent of tumor involvement in the bladder. PET can use a variety of metabolically active radiotracers to visualize cancerous tissue, allowing the identification of metastases that may not be readily visible on CT. PET scans can also detect disease in normally sized LNs that do not meet conventional CT size thresholds. The combination of MRI and PET scans has not been explored in detail with respect to bladder cancer workup but may theoretically combine the strengths of both approaches to provide the most comprehensive, noninvasive tool for preoperative staging, with improved sensitivity and accuracy compared to other modalities. This narrative review uses a systematic search of the PubMed database from 2000 to 2025 to analyze MRI and PET, both separately and in synergy, for the local and distant staging of bladder cancer, as well as key technical advancements in these imaging technologies. Synergy of the imaging modalities potentially increases efficacy in bladder cancer staging.