Definition of the Rectum

TLDR

The rectum’s definition varies worldwide, causing inconsistencies in trial recruitment, clinical management, and outcomes, and leading to divergent surgical and preoperative treatment approaches. The study aimed to establish a consensus definition of the rectum to standardise treatment, using a Delphi process with multidisciplinary colorectal experts from October 2017 to April 2018. Experts used the Delphi technique, with magnetic resonance imaging as the most common modality, to evaluate eleven proposed definitions and identify the sigmoid take‑off as the key landmark. Consensus was reached on the sigmoid take‑off visualised on imaging as the rectum’s definition, with 81 % agreement in the second round, 87 % satisfaction, and its routine use expected to improve tumour localisation consistency.

Abstract

The wide global variation in the definition of the rectum has led to significant inconsistencies in trial recruitment, clinical management, and outcomes. Surgical technique and use of preoperative treatment for a cancer of the rectum and sigmoid colon are radically different and dependent on the local definitions employed by the clinical team. A consensus definition of the rectum is needed to standardise treatment.The consensus was conducted using the Delphi technique with multidisciplinary colorectal experts from October, 2017 to April, 2018.Eleven different definitions for the rectum were used by participants in the consensus. Magnetic resonance imaging (MRI) was the most frequent modality used to define the rectum (67%), and the preferred modality for 72% of participants. The most agreed consensus landmark (56%) was "the sigmoid take-off," an anatomic, image-based definition of the junction of the mesorectum and mesocolon. In the second round, 81% of participants agreed that the sigmoid take-off as seen on computed tomography or MRI achieved consensus, and that it could be implemented in their institution. Also, 87% were satisfied with the sigmoid take-off as the consensus landmark.An international consensus definition for the rectum is the point of the sigmoid take-off as visualized on imaging. The sigmoid take-off can be identified as the mesocolon elongates as the ventral and horizontal course of the sigmoid on axial and sagittal views respectively on cross-sectional imaging. Routine application of this landmark during multidisciplinary team discussion for all patients will enable greater consistency in tumour localisation.