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

Aims Adequate case selection for intermuscular local excision (LE) of early rectal cancer (RC) using optical diagnosis and radiological imaging remains challenging and may lead to both unnecessary radical surgery, as well as incomplete LE of≥pT2 RC. We aimed to investigate whether preservation of at least 1 mm of muscularis propria on MRI, evaluated using a systematic reporting approach, can identify RC suitable for LE in the intermuscular plane.

Methods Twelve abdominal radiologists from the Netherlands underwent a one-day training session by an expert radiologist (GB).After training, all radiologists reassessed a retrospective cases series of pseudonymized MRI scans, blinded to original reports and final histology. Scans were obtained from consecutive patients suspected of having (at least) deep submucosal invasive RC at optical diagnosis between 2018 and 2022, from 2 academic centers in the Netherlands. The primary outcome was the accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the 1 mm preservation criterion on MRI in identifying tumours suitable for LE based on expert radiologist, study radiologist, and consensus diagnosis. Tumours suitable for LE were defined as RC not invading beyond the circular m. propria (≤pT2_Circ). Consensus diagnosis was based on the agreement of both study radiologists, with the expert diagnosis being decisive in case of disagreement.

Results 245 patients were included (median age 67 years [IQR 13], 71% male, 87% ASA I/II). The original MRI report showed cT0 in 2 (0.8%), cT1 in 7 (3%), cT1-T2 in 141 (58%), cT2 in 40 (17%), cT3 in 51 (21%), and cT4 in 1 (0.4%) patient (not assessable in 3). Histology showed 18 (7%) non-invasive polyps, 110 (45%) pT1 RC, 56 (23%) pT2_circ RC, 21 (9%) pT2_long RC, 39 (16%) pT3 RC, and 1 (0.4%) pT4 RC. Overall accuracy of MRI in identifying RC suitable for intermuscular LE was 80% (95% CI 75-85) for expert radiologist diagnosis and 77% (95% CI 71-82) for trained study radiologists (range individual radiologists: 64%-95%). Sensitivity, specificity, PPV, and NPV were 84%, 69%, 89%, and 59% for expert diagnosis, and 78%, 75%, 91%, and 53% for trained study radiologists, respectively. Through consensus diagnosis, accuracy at the level of the expert radiologist was achieved (accuracy: 81%, sensitivity: 84%, specificity: 74%, PPV: 91%, NPV: 60%)

Conclusions Preservation of at least 1 mm of the m. propria on rectal MRI is an accurate criterion which is easily trained and that can support adequate case selection for rectal-preserving intermuscular LE of RC.

 

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Conflicts of interest

Authors do not have any conflict of interest to disclose.

Publication History

Article published online:
15 April 2024