Single phase CT angiographic collateral scores in acute stroke

Last revised by Francis Deng on 9 Dec 2021

There are several described single-phase CT angiography collateral scores for evaluating the status of collateral vessels in acute ischemic stroke. These scores have been shown to be reliable predictors of clinical outcomes and eligibility for mechanical thrombectomy (endovascular clot retrieval) 1.

Based on single-phase CTA raw data and MIP (maximum intensity projection) images in patients with unilateral anterior circulation infarct with variable occlusion involving the MCA with or without ICA occlusion 2,3. On a scale of 0 to 3, higher grades are associated with smaller pretreatment CT perfusion parameters (MTT, CBF and CBV), final infarct volume, smaller thrombus extent and improved functional outcomes 2

  • 0: absent collateral supply to the occluded MCA territory
  • 1: collateral supply filling ≤50% but >0% of the occluded MCA territory
  • 2: collateral supply filling >50% but <100% of the occluded MCA territory
  • 3: 100% collateral supply of the occluded MCA territory

This collateral score was based on single-phase CTA source images of the collateral vessels in the Sylvian fissure and leptomeningeal convexities 4. Patients included in the study presented with M1 and/or M2 segmental occlusion in the absence of contralateral MCA or ICA occlusion and were compared to controls who had similar anterior circulation symptoms but no CTA evidence of ICA or MCA occlusion. The scale is from 1 to 5:

  • 1: absent
  • 2: less than the contralateral normal side
  • 3: equal to the contralateral normal side
  • 4: greater than the contralateral normal side
  • 5: exuberant

Based on single-phase CTA MIP images in patients with terminal ICA or proximal MCA occlusions 5, this collateral score is a modified version of that proposed by Tan et al 2. It is on a scale of 0 to 4, with higher grades correlating with better DWI admission lesion size and functional outcomes: 

  • 0: absent collaterals in >50% of an MCA M2 branch (superior or inferior division) territory
  • 1: diminished collaterals in >50% of an MCA M2 branch territory
  • 2: diminished collaterals in <50% of an MCA M2 branch territory
  • 3: collaterals equal to the contralateral hemisphere
  • 4: increased collaterals

A simplified, three-level categorization has been used in anterior proximal large vessel occlusion to identify those with low rate of ischemic core growth ("slow-progressing stroke") and likely to benefit from late window thrombectomy 6. A symmetric collateral pattern is specific for small ischemic core volume at 24 hours.

  • symmetric: contrast enhancement that appears similar or near-similar in conspicuity (no or minimally detectable reduction in opacification) of the ischemic compared to the nonischemic middle cerebral artery territory at risk
  • other: any pattern intermediate to symmetric and malignant
  • malignant: no contrast enhancement viewed over at least 50% of the middle cerebral artery territory at risk

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