- Design
- Retrospective diagnostic accuracy study with three independent readers
- Population
- 587 patients with multiparametric bladder MRI before surgery
- Primary outcome
- Inter-reader agreement on VI-RADS quality and accuracy for muscle invasion
- Effect
- Quality kappa 0.628–0.702; tumours <3 cm PPV 51.0% vs 22.7% by quality
A retrospective study of 587 patients with multiparametric bladder MRI before surgery had two genitourinary radiologists and one non-specialist independently assign VI-RADS categories and the VI-RADS quality score (0 to 2).
About half the scans scored the top quality grade (50.4%), 48.4% scored 1 and 1.2% scored 0. Agreement on quality was substantial (kappa 0.628 to 0.702). In tumours under 3 cm, higher quality was associated with a higher positive predictive value for muscle invasion at the VI-RADS 3 or higher threshold (51.0% vs 22.7%) and better accuracy (81.6% vs 71.7%), mainly for the less experienced reader. In tumours of 3 cm or more, quality made no significant difference.
The finding about reader experience rests on a single non-specialist reader and needs confirmation. The practical point is clear enough: for small tumours, a poor-quality study undermines the score.
- Record the VI-RADS quality score alongside the VI-RADS category in every bladder MRI report.
- Be cautious about calling muscle invasion in a tumour under 3 cm on a suboptimal study.
- Check bladder distension and motion before the patient leaves the scanner, and repeat sequences if needed.
- Consider specialist review of small tumours read by non-genitourinary radiologists when quality is suboptimal.
Why it matters
Bladder MRI is spreading beyond specialist centres, where image quality and reader experience vary most.
Don't overread it
The reader-experience effect rests on one less experienced reader and needs external validation.
The statistics, in plain English
Positive predictive value is the share of positive calls that were truly muscle-invasive. Rising from 22.7% to 51.0% means a positive call on a good-quality scan was right about twice as often. Weighted kappa of 0.63 to 0.70 means substantial agreement between readers.
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