Identification of 1 mm of preserved muscularis propria on MRI accurately identifies early rectal cancers suitable for local excision in the intermuscular plane

Background and Study Aims: Selection of rectal cancer cases suitable for endoscopic intermuscular dissection (EID) is challenging. We aimed to evaluate whether identification of ≥ 1mm of preserved muscularis propria on MRI, using a systematic MRI reporting tool (mrSRT), can identify rectal cancers suitable for EID. Patients and methods: Twelve radiologists underwent training in the mrSRT by an expert radiologist. The radiologists then assessed a retrospective case series of MRIs from 269 consecutive patients with suspected deep submucosal invasive rectal cancer. The primary objective was to determine the diagnostic accuracy of preservation of ≥1mm of muscularis propria on MRI for selecting cases that can be resected with clear margins using EID (invasion limited to the circular muscularis propria (≤pT2_circ)). Diagnostic accuracy was calculated for the expert radiologist, study radiologists, and a consensus diagnosis. Results: After applying the inclusion and exclusion criteria, a total of 244 patient scans were included in the analysis. Histological classification confirmed 18 (7%) lesions were non-invasive, 109 (45%) were pT1, 56 (23%) were pT2_circ , 21 (9%) were pT2_long, 39 (16%) were pT3, and 1 (0.4%) was pT4. The overall diagnostic accuracy of the ≥ 1 mm of preserved muscularis propria criterion was 81% (95%CI 75-85) for the expert radiologist diagnosis, 77% (95%CI 72-83) for the trained study radiologists, and 82% (95%CI 76-86) for a consensus diagnosis. Conclusion: Use of mrSRT to identify ≥1mm of preserved muscularis propria on MRI allows radiologists to assist in appropriate case selection for EID.

Publication History

Received: 06 December 2024

Accepted after revision: 23 May 2025

Accepted Manuscript online:
26 May 2025