Endoscopic intermuscular dissection (EID) and per anal endoscopic myectomy (PAEM) are advanced techniques derived from endoscopic submucosal dissection (ESD) in which the dissection plane extends into the muscularis propria. These techniques enable en bloc resection of rectal lesions with severe fibrosis or deep submucosal invasion, as reported in recent series. In our center, EID is planned for lesions with optical suspicion of deep invasion, whereas PAEM is performed as a salvage technique when unexpected fibrosis or deep invasion is encountered during ESD. The aim of the study was to evaluate the efficacy (technical success, R0 resection, and curative resection) and safety of EID and PAEM in rectal lesions. As a secondary aim, to compare R0 and curative resection rates with those of rectal ESD in pT1 lesions.

Multicenter cohort study based on a prospective consecutive registry. Patients ≥18 years with rectal lesions treated with ESD, EID, or PAEM were included. Non-adenoma/adenocarcinoma histologies were excluded. Curative resection was defined as pT1, G1–G2 differentiation, absence of lymphovascular invasion, low tumor budding, and a deep free margin ≥0.1 mm.

A total of 176 procedures were included (EID: 9; PAEM: 13; ESD: 154). Mean age was 67 years (SD 11.7); 51.7% were men.

Technical success with en bloc resection was achieved in 100% of EID and PAEM cases, and in 99.4% and 96.8% respectively in the ESD group. R0 resection was obtained in 9 (100%) cases in EID, 122 (79%) in ESD, and 8 (61.5%) in PAEM. Considering only pT1 lesions, R0 rates were 100% for EID, 80% for PAEM, and 47.1% for ESD. Curative resection among pT1 lesions was achieved in 2 (50%) with EID, 2 (15.4%) with PAEM, and 5 (29.4%) with ESD.

Median procedure time was 85 minutes (IQR 70–114) for EID and 145 minutes (IQR 108–285) for PAEM. Dissection speeds were: EID 21.3 mm²/min (SD 9.2), PAEM 21.6 mm²/min (SD 13.1), and rectal ESD 28.8 mm²/min (SD 16). Median hospital stay was 1 day (IQR 1–2) in both groups.

Adverse events included mild post-procedural pain in 1 EID (11.1%) and 1 PAEM (7.7%) case, and abdominal pain prolonging admission by 1 day in 1 EID patient (11.1%). A stenosis occurred in 1 PAEM case (7.7%), successfully managed with three dilation sessions. One PECS-like reaction occurred in the EID group (11.1%).

EID and PAEM are effective and safe techniques for complex rectal lesions, achieving high R0 rates in pT1 tumors with curative potential. These methods represent valuable options within organ-preserving strategies for selected rectal neoplasms.