The Role of Collateral Circulation in Acute Ischemic Stroke Outcomes: A Systematic Review and Meta Analysis of Clinical Trials

Introduction: Acute ischemic stroke (AIS) remains a leading cause of disability and death, with timely reperfusion being critical for patient outcomes. Collateral circulation plays a key role in sustaining brain tissue at risk, delaying infarct progression, and extending the therapeutic window. This systematic review explores the impact of collateral status on functional outcomes and treatment efficacy, emphasizing advancements in imaging for optimal patient selection.

Methods: This systematic review followed PRISMA guidelines. A comprehensive search of PubMed, EMBASE, and Web of Science was conducted up to October 2024, including only clinical trials that reported collateral status, neurological outcomes, and reperfusion success. Data were extracted using Covidence, and study quality was assessed with the Joanna Briggs Institute tool. Statistical analyses were performed using Microsoft Excel and JMP.

Results: A total of 61 clinical trials were included, categorized into treatment windows of < 6 hours, 6-24 hours, and >24 hours from symptom onset, with the majority of patients (61.67%) treated within 6 hours. Good collateral status was consistently associated with better reperfusion outcomes, with mTICI 2b-3 scores demonstrating superior success rates in patients with favorable collaterals compared to those with poor collaterals. Endovascular interventions showed more promising revascularization results compared to IV thrombolysis. Advanced imaging techniques, such as multiphase CTA and perfusion imaging, were crucial for assessing collateral flow and guiding treatment. Despite differences in timing, complication rates, including symptomatic hemorrhage, remained similar across groups.

Conclusion : Collateral circulation significantly impacts outcomes in AIS, highlighting the importance of early intervention and accurate assessment. The < 6-hour treatment window consistently demonstrated better neurological outcomes, and patients with robust collateral grades experienced higher reperfusion success. Utilizing advanced imaging techniques, such as multiphase CTA and perfusion imaging, enhances treatment decision-making and may improve patient prognosis. Ongoing research is essential to further optimize collateral evaluation and tailor therapeutic strategies for improved outcomes.