Prevention of Parastomal Hernia With Funnel-Shaped Intra-Abdominal Mesh vs No Mesh for Rectal Adenocarcinoma Surgery

Importance: Parastomal hernia (PSH) is one of the most common complications after permanent colostomy, yet there is ongoing debate regarding the effectiveness and indications of preventive measures. Objective: To evaluate the effectiveness and safety of funnel-shaped mesh in preventing PSH over a 3-year follow-up period. Design, Setting, and Participants: The Chimney Trial was a randomized, single-blinded, multicenter study conducted at 4 university and central hospitals in Finland and 1 central hospital in Sweden. This study presents the 3-year follow-up results. Of 439 screened patients undergoing laparoscopic or robotic abdominoperineal excision or Hartmann procedure for rectal adenocarcinoma, 143 were randomized (68 to the mesh group and 67 to the control group). At 3 years, 50 patients in the mesh group and 51 in the control group were available for analysis; computed tomography (CT) scans were obtained in 44 and 39 patients, respectively. These data were analyzed from September 2025 to December 2025. Intervention: Placement of a funnel-shaped parastomal mesh vs no mesh at the time of abdominoperineal excision or Hartmann procedure. Main Outcomes and Measures: CT-confirmed PSH at 3-year follow-up. Results: The Chimney Trial included a total of 101 patients (39 female [39%] and 63 male [61%]). At 3 years, CT-confirmed PSH was observed in 25 of 44 patients (57%) in the mesh group and 32 of 39 patients (82%) in the control group (difference, -25%; 95% CI, -42% to -5%; P = .001). Clinically diagnosed PSH occurred in 5 of 50 patients (10%) vs 20 of 51 patients (39%) in the control group (difference, -29%; 95% CI, -44% to -13%; P < .001). PSHs were significantly larger in the control group compared with the mesh group (median [IQR], 86.8 [53.0-136.5] mL for the mesh group vs 185.9 [118.0-411.2] mL for the control group; P = .003). No significant differences were observed in other secondary outcomes. Conclusions and Relevance: In this study, funnel-shaped mesh significantly reduced PSH incidence without increasing complications over a 3-year follow-up period. These findings support the use of a funnel-shaped mesh as an effective and safe preventive strategy to reduce the risk of parastomal hernia after permanent colostomy. Trial Registration: ClinicalTrials.gov Identifier: NCT03799939.