Background and purpose To systematically review and meta-analyse the data on impact of timing of endovascular treatment in aneurysmal subarachnoid haemorrhage (SAH) to determine if earlier treatment is associated with improved clinical outcomes and reduced case fatality.

Methods We searched MEDLINE, Cochrane database, EMBASE and Web of Science to identify studies for inclusion. The measures of effect utilised were unadjusted/adjusted ORs. Effect estimates were combined using random effects models for each outcome (poor outcome, case fatality); heterogeneity was assessed using the I² index. Subgroup and sensitivity analyses were performed to account for heterogeneity and risk of bias.

Results 16 studies met the inclusion criteria. Treatment <1 day was associated with a reduced odds of poor outcome compared with treatment >1 day (OR=0.40 (95% CI 0.28 to 0.56; I²=0%)) but not when compared with treatment at 1–3 days (OR=1.16 (95% CI 0.47 to 2.90; I²=81%)). Treatment at <2 days and at <3 days were associated with similar odds of poor outcome compared with later treatment (OR=1.20 (95% CI 0.70 to 2.05; I²=73%; OR=0.71 (95% CI 0.36 to 1.37; I²=71%)). Early treatment was associated with similar odds of case fatality compared with later treatment, regardless of how early/late treatment were defined (OR=1.80 (95% CI 0.88 to 3.67; I²=34%) for treatment <1 day vs days 1–3; OR=1.71 (95% CI 0.72 to 4.03; I²=54%) for treatment <2 days vs later; OR=0.90 (95% CI 0.31 to 2.68; I²=48%) for treatment <3 days vs later).

Conclusions In only 1 of the analyses was there a statistically significant result, which favoured treatment <1 day. The inconsistent results and heterogeneity within most analyses highlight the lack of evidence for best timing of endovascular treatment in SAH patients.