Collateral Circulation- Evolving from Time Window to Tissue Window.

Cerebral collateral circulation refers to the auxiliary vascular structures which compensate cerebral blood flow when it has been compromised due to stenosis or occlusion of the principal supplying arteries. They play a vital role in sustaining blood flow to the ischemic areas in acute, subacute or chronic phases of ischemic stroke or TIA. Good collateral circulation has shown protective effects towards a favorable functional outcome and a lower risk of recurrence of stroke. The benchmark mechanical thrombectomy trials utilized these collateral scoring methods to guide patient selection and prognosticate favorable outcome models. This shows a promising future of the collateral circulation for extending the time frame of the reperfusion therapies by optimally guiding patient selection and moving from a "time window" to a "tissue window."