Essential anatomy for total mesorectal excision and lateral lymph node dissection, in both trans-abdominal and trans-anal perspective

Background and Purpose Total Mesorectal Excisions (TME) is the standard treatment of rectal cancer. It can be performed under laparoscopic, robotic or transanal approach. Inadvertent injury to surrounding structure like autonomic nerves is avoidable, no matter which approach is adopted. Lateral lymph node dissection (LLND) is a less commonly performed pelvic operation involving dissection in an unfamiliar area to most general surgeons. This article aims to clarify all the essential anatomy related to these procedures. Methods We performed thorough literature search and revision on the pelvic anatomy. Our cases of TME and LLND, under either laparoscopic or transanal approach, were reviewed. We integrated the knowledge from literatures and our own experience. The result was presented in details, together with original figures and intra-operative photos. Main findings Anatomy of pelvic fascia, autonomic nerve system, anal canal and sphincter complex are core knowledge in performing TME and LLND. Conclusions Thorough understanding of the pelvic anatomy enables colorectal surgeons to master these procedures, avoid complication and perform extended resection. On the other hand, surgeons can appreciate the complex pelvic anatomy easier by seeing the pelvis in opposite angles (transabdominal and transaanal view).