VI-RADS score system - A primer for urologists

Abstract

Bladder cancer (BCa) is one of the most common cancers worldwide and is also considered to be one of the most relapsing and aggressive neoplasms. About 30% of patients will present with muscle invasive disease, which is associated with a higher risk for metastatic disease. The aim of this article is to review the state of art imaging in Radiology, while providing a complete guide to urologists, with case examples, for the rationale of the development of the Vesical Imaging Reporting and Data System (VI-RADS), a scoring system emphasizing a standardized approach to multiparametric Magnetic Resonance Imaging (mpMRI) acquisition, interpretation, and reporting for BCa. Also, we examine relevant external validation studies and the consolidated literature of mpMRI for bladder cancer. In addition, this article discusses some of the potential clinical implications of this scoring system for disease management and follow-up.

Keywords: Diffusion Magnetic Resonance Imaging; Genitourinary Tract Anomalies [Supplementary Concept]; Urinary Bladder Neoplasms.

Figure 1. These pictures illustrate how structural categories (T2 images) of VI-RADS are assigned. The muscularis propria is presented as a thick black layer. The inner layer (urothelium + lamina propria) is a thin white layer. The tumors are shown in grey and the stalk, when present, in black, in continuity with the muscular layer. The inner layer is preserved in categories 1 and 2. In category 3, the inner layer is not seen, but there is no clear sign of muscle invasion. In categories 4 and 5, the tumors have extended to the muscular layer, and in VI-RADS 5, they go beyond, until perivesical fat.

Figure 2. A 72-year-old woman presented with macroscopic hematuria. A) T2W image (axial plane) shows a large stalked mass at the anterior bladder wall. B and C) DWI (b=2000) and ADC maps show significantly restricted diffusion, not extending through the muscularis propria; the “inchworm” sign can be appreciated. D) DCE imaging shows early and heterogeneous enhancement of the lesions, not extending through the muscularis propria. The final VI-RADS score was 2. T2W, T2 weighted; DCE, dynamic contrast-enhanced; DWI, diffusion-weighted image; ADC, apparent diffusion coefficient.

Figure 3. A 46-year-old, female, complains of frequency, urgency, and severe incontinence. A pelvic sonogram showed moderate to marked left hydronephrosis and asymmetric bladder wall thickening on the top portion of her bladder. A and B) Axial and Coronal T2-weighted MRI of the pelvis demonstrates a 4.4 x 3.6cm mass extending to muscle layer. C) ADC map in the axial plane, and D) T1 post-contrast, also in the axial plane, confirming that mass shows extension into the muscular layer. This was consistent with VI-RADS 4, confirmed after surgery.

Figure 4. The decision algorithm for VI-RADS. When all categories are coincident, the final score is directly assigned. When classification in different sequences is discordant, DCE, and DWI are the dominant sequences and will prevail for the final classification. As seen in figure 4, DCE and DWI can upgrade or downgrade the initial classification found on T2 images.