Defining the Rectum and Sigmoid Colon: Should We Abolish the Term 'Rectosigmoid' to Improve Outcomes in Colorectal Cancer?

The risk of circumferential resection margin (CRM) involvement is conned to tumours of the rectum with the risk of peritoneal involvement increasing the further a tumour is located above the peritoneal reection. There is no internationally accepted denition of the upper limit of the rectum, and the term ‘rectosigmoid’ is frequently applied to tumours in this area leading to confusion around the risks and whether radiotherapy can be given. The photographs from 331 abdominoperineal excision specimens were available for quantitation using Aperio ImageScope. Both fresh and xed specimen images were included where available. The position of the anal verge, top of the sphincters, anterior peritoneal reection, mesorectal apex (dening the limit of the mesorectum) and high vascular tie were identied and the distances between each point measured. The work was supported by a PathSoc bursary. There was wide variation in the length of the mesorectum in both fresh (median 172 mm, IQR 146 to 199 mm) and xed (166 mm, 140 to 196 mm) specimens. The length of the anal canal also showed variation (fresh 66 mm, 49 to 78 mm; xed 66 mm, 53 to 75 mm). The height of the anterior peritoneal reection was lower in females compared to males (fresh 125 vs. 132 mm, p=0.288; xed 111 vs. 126 mm, p=0.034). There is marked variability in the anatomy of the rectum between individuals and genders. This potentially aects the risk of either CRM or peritoneal involvement and whether radiotherapy could be oered. A xed denition of the upper limit of the rectum for all patients is not helpful. This should be determined for individual patients on the basis of the MRI ndings. The term ‘rectosigmoid’ should be abolished and more accurate denitions based on the position of the mesorectal apex and commencement of the sigmoid mesentery should be used to dene the boundaries of the rectum and sigmoid colon and determine subsequent risks to the patient.