Transanal Total Mesorectal Excision for Rectal Cancer on Anal Physiology + Fecal Incontinence

Primary Objective To evaluate effect of TaTME on anal sphincter via anorectal functional studies and anorectal ultrasound administered post- and preoperatively. Secondary Objective(s) To evaluate the effect of TaTME on fecal incontinence, quality of life, and LARS utilizing validated questionnaires administered to patients preoperatively and during postoperative follow-up. Study Design This is a prospective two-arm cohort study. The study will include patients already undergoing the standard-of-care, low anterior resection (LAR) for middle to low rectal cancers. Low anterior resection of the rectum entails a sharp dissection circumferentially around the mesorectum in an avascular plane between the visceral and parietal layers of the endopelvic fascia in what is known as Total Mesorectal Excision (TME). This dissection can be achieved transanally starting down in the pelvis and going up in what is known as Transanal Total Mesorectal Excision- (TaTME). It can also be done via an up-to-down approach beginning high in the abdomen and going low in the pelvis to achieve dissection around the mesorectum. Access in the latter is achieved via laparoscopic or open abdominal incisions with minimal anal sphincter dilation. In addition, the level of coloanal anastomosis performed is potentially higher from the anal sphincter in comparison to TaTME. TaTME on the other hand, involves introducing a special port (gelpoint path) transanally to perform the TME dissection. In order to better evaluate the effect of TaTME on anal sphincter, it is quintessential to include a control group with minimal anal sphincter manipulation, thus the conventional abdominal (open or laparoscopic) TME group will serve as a control.