Variation in assessment of dissection plane after transanal total mesorectal excision (TaTME) among experienced colorectal pathologists

Abstract Purpose Evaluation of the dissection plane is an important measure of surgical quality in relation to rectal cancer. Although well-defined criteria exist assessments may vary. The aim of this study was to assess variation in the evaluation of dissection plane of transanal total mesorectal excision (TaTME) specimens, when performed by experienced colorectal pathologists. Methods Photos of fresh surgical specimens were collected from a prospectively registered nationwide cohort and divided in two datasets. Blinded re-evaluation of the first half was performed by four pathologists. Concordance with original evaluation and interrater variability was determined by kappa statistics. This was followed by an educational module, where cases and assessment were discussed. Re-evaluation of the second half of cases was then performed. Results One hundred six cases were included. The original evaluation of dissection plane was 63 (60%) mesorectal plane, 30 (28%) intramesorectal plane, and 13 (12%) muscularis plane. In the first half agreement between the original and the re-evaluation ranged from fair to moderate. Overall interrater agreement was fair (Fleiss’ kappa (95% CI) 0.38 (0.28–0.47)), with slightly better agreement concerning muscularis plane. Agreement between the original and the second half (after the educational/harmonizing effort) was fair to good. Overall interrater agreement increased to moderate (Fleiss’ kappa (95% CI) 0.56 (0.47–0.65)), with the primary improvement in the agreement on muscularis plane. Conclusion The study showed considerable variation in the assessment of dissection plane after TaTME, even among experienced colorectal pathologists. Variation slightly diminished following discussion especially for muscularis plane where good agreement was obtained.