Abstract: Randomized controlled trials (RCT) Only one RCT met the inclusion criteria. The participants underwent enterostomy placement in the frame of an operation for: rectal cancer (37/60), ulcerative colitis (14/60), familial adenomatous polyposis (7/60), and other (2/60). The results between the lateral pararectal and the transrectal approach groups were inconclusive for the incidence of parastomal herniation (risk ratio (RR) 1.34, 95% confidence interval (CI) 0.40 to 4.48; low-quality evidence); development of ileus or stenosis (RR 2.0, 95% CI 0.19 to 20.9; low-quality evidence); or skin irritation (RR 0.67, 95% CI 0.21 to 2.13; moderate-quality evidence). The results were also inconclusive for the subgroup analysis in which we compared the effect of ileostomy versus colostomy on parastomal herniation. The study did not measured other stoma-related morbidities, or stoma-related mortality, but did measure quality of life, which was not one of our outcomes of interest. Non-randomized studies (NRS) Ten retrospective cohort studies, with a total of 864 participants, met the inclusion criteria. The indications for enterostomy placement and the baseline characteristics of the participants (age, co-morbidities, disease-severity) varied between studies. All included studies reported results for the primary outcome (parastomal herniation) and one study also reported data on one of the secondary outcomes (stomal prolapse). The effects of different surgical approaches on parastomal herniation (RR 1.22, 95% CI 0.84 to 1.75; 10 studies, 864 participants; very low-quality evidence) and the occurrence of stomal prolapse (RR 1.23, 95% CI 0.39 to 3.85; 1 study, 145 participants; very low-quality evidence) are uncertain. None of the included studies measured other stoma-related morbidity or stoma-related mortality. The present systematic review of randomized and non-randomized studies found inconsistent results between the two compared interventions regarding their potential to prevent parastomal herniation. In conclusion, there is still a lack of high-quality evidence to support the ideal surgical technique of stoma formation. The available moderate-, low-, and very low-quality evidence, does not support or refute the superiority of one of the studied stoma formation techniques over the other.

Plain-language summary: The evidence is current to 9 November 2018. In this update, we included 10 retrospective cohort studies with a total of 864 participants, and one randomized controlled trial (RCT: a study in which participants are randomly allocated to the treatment groups), including 60 participants. The target population was individuals, regardless of age, who received a temporary or permanent enterostomy for any reason in either the elective (planned) or the emergency setting. The results found inconclusive results between the two techniques for the risk of parastomal herniation (11 studies, 924 participants), stomal prolapse (1 study, 145 participants), ileus or stenosis (1 study, 60 participants), and skin irritation (1 study, 60 participants). Neither technique was found to be better than the other for any of the stoma-related outcomes of interest. None of the studies measured other stoma-related problems, or death. We downgraded the quality of the evidence to moderate, low, or very low, because of high risk of bias, small sample sizes, few events, and diversity across studies. Based on the current knowledge presented in this review, there is no evidence to support the use of one stoma formation technique over the other. Further research is likely to have an important impact on our confidence in the estimate of effect.