Table 1

Examples of collateral grading methods based on CTA

Collateral grading methodsGrading criteria
Miteff collateral grading method35 Collateral status is graded in maximum intensity projection reconstructions of single-phase CTA in axial, coronal and sagittal planes in patients with MCA occlusion, and graded as:

  • Good, if major MCA branches are reconstituted distal to the occlusion.

  • Moderate, if some MCA branches are shown in the Sylvian fissure.

  • Poor, if only the distal superficial MCA branches are reconstituted.

Maas collateral grading method36 Collateral vessels in the Sylvian fissure and the leptomeningeal convexity are graded in CTA source images by comparing the symptomatic hemisphere with the contralateral unaffected hemisphere as:
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.		The presence and status of the anterior and posterior communicating arteries are graded as:
1=Absent.
2=Probably present.
3=Hairline.
4=Definitely present.
5=Robust.
Tan collateral grading system37 Leptomeningeal collateral status is graded in source images and maximum intensity projection reconstructions of single-phase CTA as below, with scores of 0–1 as poor and 2–3 as good collateral status.
0=No collateral supply to the occluded MCA territory.
1=Collateral supply filling ≤50% 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.
Regional leptomeningeal collateral (rLMC) score38 The rLMC score (20 points) compares the extent of contrast opacification in arteries distal to an M1 MCA occlusion (±internal carotid artery occlusion) in the symptomatic hemisphere with the contralateral hemisphere in multiplanar reformatted CTA, with a higher score indicating a better collateral status.
The extent of contrast opacification is scored as 0 (artery not seen), 1 (less prominent) or 2 (equal or more prominent than the opposite hemisphere) for the six ASPECTS cortical regions (M1–6), parasagittal ACA territory and the basal ganglia, while pials in the Sylvian sulcus are given a higher score, that is, 0, 2 or 4.
ACA-MCA and PCA-MCA regional collateral score39 40 The scoring system assesses the extent and prominence of pial arteries in the ACA-MCA and PCA-MCA regions, in patients with stroke with M1 MCA occlusion±intracranial internal carotid artery occlusion, in two-dimensional multiplanar reconstructions of dynamic CTA. Collaterals in the ipsilesional ACA-MCA and PCA-MCA regions are each scored as 0–5 as below by comparing with the contralateral hemisphere, while the total score ranges from 0 to 10.
0=Absent.
1=Minimal.
2=Significantly decreased prominence and extent of pial arteries.
3=Moderately decreased prominence and extent.
4=Mildly decreased prominence and extent.
5=Normal or increased prominence and extent.

  • ACA, anterior cerebral artery; ASPECTS, the Alberta Stroke Programme Early CT Score; CTA, CT angiography; MCA, middle cerebral artery; PCA, posterior cerebral artery.