A tailored mesorectal excision (also referred to as a partial mesorectal excision or tumor-specific mesorectal excision) can be employed for cancers in the upper and upper-mid rectum. The rationale for a 5-cm distal margin is based upon data showing longitudinal spread within the tubular lymphatics and lymph nodes of the rectum extending from 2 to 4 cm distal to the lesion.[1],[2] For upper rectal cancers, a distal mesorectal margin of 5 cm should be obtained, including rectum and mesorectum. However, for lesions in lower-mid and distal rectum, a total mesorectal excision is performed that includes all lymphatics and lymph nodes associated with cancer in this location. For lower cancers following neoadjuvant therapy, a distal rectal wall margin as small as 1 cm can be adequate in order to achieve sphincter preservation with good oncologic control.[3],[4],[5]

Total mesorectal excision is associated with high incidence of anastomotic leak that in part is due to devascularization of the distal “bared” rectal muscular tube used to construct a low colorectal or colo-anal anastomosis. Partial mesorectal excision avoids devascularization of the distal rectal tube and is supported by histologic examination of extent of lymphatic cancer spread in the mesorectum distal to the cancer. Partial mesorectal excision follows the same dissection planes as total mesorectal excision except the mesorectum is divided perpendicular to the axis of the bowel when an adequate distal mesorectal margin has been assured, 5 cm distal to the distal end of the tumor. The bowel is divided at the same level as the mesorectal division (Figure 7.1).

To avoid implantation of viable cancer cells in the anastomosis, some surgeons irrigate the rectal lumen with a tumoricidal agent (e.g., sterile water, Betadine solution). This can be done trans-anally prior to stapling and dividing the rectum. One technique for doing this is to clamp the rectum distal to the cancer and superior to the point of transection. Then the irrigation is performed, followed by dividing the rectum distal to the clamp.