Single phase CT angiographic collateral scores in acute stroke

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.

Tan et al

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

Maas et al

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

Souza et al

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

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