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Circumferential resection margin (CRM) is essential for oncological quality assessment in rectal cancer surgery. CRM represents a surrogate parameter for oncological outcomes and is important for stratifying treatment strategies in Western nations. In Japan, the mesentery is removed for specimen processing in order to extract as many lymph nodes (LNs) as possible; consequently, CRM cannot be measured. Given the diversification of treatment strategies for rectal cancer, the lack of measurement of CRM to assess surgical outcomes is a crucial issue that must be resolved. Therefore, it is necessary to establish a method enabling measurement of CRM while enjoying the advantages of the Japanese method. In the method we developed, the mesentery is removed from the rectum more than 2 cm away from the tumor, and the vicinity of the tumor is circularized. It is necessary to investigate the usefulness of this method prospectively in a multi-center study.

Introduction Transperineal minimally invasive abdominoperineal excision (TpAPE) may help minimize surgical invasiveness and make it possible to perform two-team surgery, although this procedure is regarded as difficult. The anatomical structures are complicated and have not been clearly defined, particularly on the anterior side of the anorectal junction in men. We investigated the anatomical configuration around the anterior wall of the anorectal junction, focusing on the structure of the striated muscles, to establish a standard procedure for TpAPE. Methods We scrutinized the T2 -weighted MRI scans of 106 men, and two male cadavers were used to examine the muscular structure surrounding the anorectal junction. We established our standardized procedure for TpAPE based on these anatomical studies. We also analyzed the clinicopathological findings from five men who had undergone TpAPE at our institution. Results Using MRI, we detected band-like muscles bilaterally, just medial to the puborectal muscle in all analyzed patients, which we termed the rectal anterolateral muscle. We also detected the muscles that may correspond to the rectal anterolateral muscle when inspecting the cadavers. The standardized TpAPE procedures were carried out uneventfully for the five cases, and intraoperative complications such as urethral injury and inadvertent rectal perforation did not occur. Conclusion We standardized the TpAPE procedure based on anatomical examination of the muscular structure around the anal canal. The findings can contribute to safe implementation of TpAPE.