The ASITN/SIR collateral-flow grading system to determine angiographic collateral grade on pretreatment angiography
| ASTIN/SIR Collateral Grade | Definition |
|---|---|
| 0 | No collaterals visible to the ischemic site |
| 1 | Slow collaterals to the periphery of the ischemic site with persistence of some of the defect |
| 2 | Rapid collaterals to the periphery of ischemic site with persistence of some of the defect and to only a portion of the ischemic territory |
| 3 | Collaterals with slow but complete angiographic blood flow of the ischemic bed by the late venous phase |
| 4 | Complete and rapid collateral blood flow to the vascular bed in the entire ischemic territory by retrograde perfusion |
Note:—ASTIN/SIR indicates American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology.7