Is a virtual scale a better option for polyp size measurement?

We read with interest that a virtual scale has been reported to measure polyp size with high accuracy [1] [2]. The work by van Bokhorst et al. [3] further indicated that using a virtual scale to measure polyp size resulted in less variability in polyp size measurement. Despite the promising findings, several issues should be addressed.

First, the classifying performance of the virtual scale for polyp size types was suboptimal (<70%), and compared with visual and snare measurement, the mean error was also the largest (using histopathological measurement as reference), which may indicate a certain measuring variability of the virtual scale. Notably, the five participating endoscopists only graded user-friendliness of the virtual scale as 5, while no corresponding information regarding visual and snare measurements were provided to accurately evaluate the generalizability of the three methods. More relevant information should be revealed.

Second, only a 9-mm snare, without biopsy forceps, was used as a visual reference. Compared with biopsy forceps, a snare might not be accurate or suitable for predicting the size of diminutive polyps in routine colonoscopy practice, which may lead to an overestimate of the error and variability of measurement. However, the virtual scale provided two modes (linear and circular) to adapt to different polyp conditions, which may further influence the robustness and convincingness of the findings.

Finally, during real-world colonoscopy, endoscopists could evaluate polyp size from a suitable angle and distance according to their own habits. The study may therefore underestimate the diagnostic performance due to incapability of finding the most suitable observing position in the video. Besides, the unsuccessful cases, which may reflect real-world measurement variability, should not been excluded completely and a sensitivity analysis with or without unsuccessful cases might provide a more comprehensive evaluation for the measuring variability and systematic differences.

Publication History

Article published online:
28 January 2025

• References

• 1 Shimoda R, Akutagawa T, Tomonaga M. et al. Estimating colorectal polyp size with a virtual scale endoscope and visual estimation during colonoscopy: prospective, preliminary comparison of accuracy. Dig Endosc 2022; 34: 1471-1477
• 2 von Renteln D, Djinbachian R, Zarandi-Nowroozi M. et al. Measuring size of smaller colorectal polyps using a virtual scale function during endoscopies. Gut 2023; 72: 417-420
• 3 van Bokhorst QNE, Houwen BBSL, Hazewinkel Y. et al. Polyp size measurement during colonoscopy using a virtual scale: variability and systematic differences. Endoscopy 2024;