Timing of aneurysm repair and clinical outcomes after aneurysmal subarachnoid hemorrhage: a systematic review

BACKGROUND: Aneurysmal subarachnoid hemorrhage (aSAH) causes substantial morbidity and mortality, and guidelines recommend aneurysm repair as early as feasible. However, the association between onset-to-treatment time and outcomes remains uncertain. This review synthesized evidence across multiple clinical outcomes and examined whether treatment modality modifies this association. METHODS: Searches were conducted in PubMed/MEDLINE, Scopus, and LILACS for studies comparing clinical outcomes across different onset-to-treatment windows in adults with confirmed aSAH. Findings were synthesized narratively according to the Synthesis Without Meta-analysis (SWiM) guideline. The review was prospectively registered in PROSPERO (CRD420261415084). RESULTS: Twenty reports comprising 11,096 participant records were included, with likely overlap between two reports. Treatment categories ranged from <6 h to ≥15 days. Earlier securement likely reduced pretreatment rebleeding, particularly when untreated or markedly delayed patients were included, although treated-cohort comparisons were inconsistent. More methodologically informative adjusted analyses showed no reproducible independent association between treatment timing and functional outcome or mortality. No consistent association emerged for vasospasm or related cerebral ischemia, hydrocephalus, or length of stay. Two observational studies modeled time continuously: one found a significant U-shaped mortality association with an estimated nadir at 32.6 h, whereas the other showed a similar but non-significant adjusted pattern with an estimated nadir near 12.16 h. These findings are highly susceptible to confounding by indication and survivor bias and do not establish benefit from treatment delay. Three studies formally tested modality-timing interaction; one found a significant mortality interaction and two did not. Additional stratified analyses showed no consistent modality-specific pattern. Certainty of evidence for the timing-mortality association was very low because of serious risk of bias, inconsistency, and imprecision. CONCLUSION: Earlier aneurysm securement remains supported for preventing pretreatment rebleeding. The independent association of treatment timing with mortality or functional outcome remains uncertain. The observed mortality patterns are hypothesis-generating and do not define a validated therapeutic window, support intentional treatment delay, or justify changing current guideline recommendations. Prospective multicenter studies using continuous-time modeling and rigorous methods to address confounding and survivor bias are needed.