Trouble in Paris (classification): polyp morphology is in the eye of the beholder.

Key challenges to colonoscopy outcomes include polyp detection, appropriate polyp resection, and prediction of recurrent polyps. The Paris classification of gastrointestinal neoplasia has been used to attempt to address these challenges based on the hypothesis that the visual appearance of a polyp (e.g., sessile, flat, depressed) has an impact on these outcomes. Although the Paris classification has been widely used as a measurement tool in research, and reported to predict outcomes such as risk for high-grade dysplasia and invasive carcinoma, interobserver variability associated with this classification scheme has not been studied. In the current issue of the Red Journal, van Doorn et al. studied the interobserver variation of Paris classification in 85 colorectal polyps assessed by seven expert colonoscopists. They found that interobserver variation measured by kappa was only moderate (kappa=0.42; 95% confidence interval: 0.39-0.45). These findings suggest that without methods to improve interobserver variability, the Paris classification cannot routinely be used for research or routine practice. New approaches to characterizing polyp appearance may be required to use morphology as a predictor of clinical outcomes.