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 lt; .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
Mäkäräinen et al. (Wed,) studied this question.