Peritoneal opening during transanal endoscopic microsurgery: can preoperative positioning assessment improve intraoperative management?

[BACKGROUND] Peritoneal opening (PO) during transanal endoscopic microsurgery (TEM) can cause the pneumorectum to collapse and complicate the procedure. As indications expand to larger, more proximal rectal lesions, understanding the real-world frequency, predictors, and consequences of PO is clinically important.

[METHODS] We analysed a prospectively maintained single-centre database (January 1993-August 2025) of consecutive TEM/TEO resections. The primary exposure was PO; outcomes included abdominal conversion, complications, and length of stay (LOS). Multivariable logistic regression evaluated factors such as distal distance from the anal verge, maximal diameter, excision plane, and simplified lesion location (anterior, posterior, lateral, circumferential). The prone/supine position was examined overall and within the PO subgroup.

[RESULTS] Of 1077 resections, PO occurred in 81/1,077 (7.5%). PO was more common with increasing distance from the anal verge: distal edge < 7 cm 2.3% (13/570) versus ≥ 7 cm 13.5% (68/502). Independent predictors included greater distance (OR 1.49 per cm; 95%CI 1.35-1.65; p < 0.001), larger diameter (OR 1.19 per cm; 95%CI 1.03-1.38; p = 0.022), full-thickness compared to submucosal excision (OR 4.03; 95%CI 1.39-11.66; p = 0.010), and circumferential versus anterior location (OR 4.78; 95%CI 1.61-14.19; p = 0.0049). Posterior location was protective (OR 0.26; 95%CI 0.13-0.53; p = 0.0002). Conversion occurred more frequently with PO (6.2%, 5/81) than without (0.1%, 1/992). LOS was longer with PO (median 5 [IQR 4-6] days) compared to without PO (median 4 [3-5] days; p < 0.001). The rate of complications did not differ significantly (any Dindo ≥ 1: 11.1% vs 7.3%; p = 0.19). Position was prone in 560/1,077 (52.2%) and supine in 513/1,077 (47.8%); PO was more common in prone (11.1%) than in supine (3.7%; p < 0.0001). Within the PO group, conversion was higher in the supine position (4/19, 21.1%) versus prone (1/62, 1.6%; p = 0.007), and laparoscopic-only conversions showed a borderline excess in the supine position (2/19 vs 0/62; p = 0.049).

[CONCLUSIONS] PO during TEM/TEO is infrequent, anatomically driven, and usually manageable with secure endoluminal repair. Careful surgical planning-considering distance, orientation, and size-and matching platform/position can reduce risk, with no evident increase in short-term morbidity.