Multiparametric MRI for Diagnosis and Staging of Bladder Cancer - Expert Commentary

Various technical limitations exist to the tools currently used to diagnose and stage bladder cancer. Some techniques for diagnosis and staging include cystoscopy, ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI). Multiparametric MRI (mp-MRI) combines T2-weighted images (T2WI) and dynamic contrast-enhanced MRI (DCE- MRI) or diffusion-weighted MRI (DWI).

Shalaby et al. aimed to evaluate mp-MRI parameters and accuracy for diagnosing and staging bladder cancer. The study included 50 patients with bladder cancer. The median age in the cohort was approximately 62 years, with 38 males and 12 females. Regarding treatment, 44% of patients with non-muscle invasive bladder cancer (NMIBC) underwent TURBT, while 40% of muscle-invasive bladder cancer (MIBC) patients underwent radical cystectomy. Histological analysis of patient samples revealed that 78% of patients had urothelial carcinoma, 10% had squamous cell carcinoma, and 12% had cystitis. 36% of cases were T1, 24% were T2, and 28% were T3b. The staging accuracy of T2WI with DCE was 75.5% for T1, 80% for T2, and 91% for T3b. The staging accuracy of T2WI with DWI was 92% for T1, 88% for T2, and 94% for T3b. The combination of T2WI, DCE, and DWI provided the highest accuracy rates of 96% for T1, 94% for T2, and 96% for T3b. T2WI and DWI led to higher accuracy in detecting muscle invasion by bladder mass (88.6%) than T2WI and DCE (79.5%). With mp-MRI (combination of T2WI, DCE, and DWI), the accuracy of muscle invasion detection reached 95.4%. When compared to standard histopathological assessment for staging, the agreement level was fair for T2WI and DCE (κ = 0.59), good for T2WI and DWI (κ = 0.74), and excellent for mp-MRI (κ = 0.83).

Researchers then analyzed the apparent diffusion coefficient (ADC) to determine whether it could be used to divide low-grade and high-grade tumors. They identified a cut-off value that accurately differentiated low-grade from high-grade tumors with a sensitivity of 93.3% and a specificity of 98.3%. The mean ADC value was significantly lower in high-grade tumors than in low-grade tumors. Lymph node evaluation using mp-MRI revealed that most patients were considered N0. When compared with pathology, the accuracy of nodal metastasis detection with mp-MRI was 85%.

Overall, mp-MRI had the highest accuracy rates. The use of this technique minimizes the risk of under-staging and over-staging. One limitation of the study is the small number of patients, which led to an uneven distribution of stages that could skew accuracy rates if the technique is better suited for detecting specific stages. Moreover, the European Association of Urology proposed a new reporting method for mp-MRI in 2018, but it was not implemented in this study. Accordingly, further validation of these findings should include a larger sample size and a new methodology for mp-MRI scoring.

Written by: Bishoy M. Faltas, MD, Director of Bladder Cancer Research, Englander Institute for Precision Medicine, Weill Cornell Medicine

References:

  1. Shalaby EA, Mohamed AR, Elkammash TH, Abouelkheir RT, Housseini AM. Role of multiparametric magnetic resonance imaging in the diagnosis and staging of urinary bladder cancer. Curr Urol. 2022;16(3):127-135. doi:10.1097/CU9.0000000000000128

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