Collateral vessels are an important consideration during the acute imaging of ischaemic stroke, as they can impact upon the evaluation of whether or not a patient will benefit from endovascular clot retrieval 1.
Studies have shown that in acute stroke, both CTA and MRA are accurate modalities in assessing the status of collateral vessels 2-4. The status of these vessels not surprisingly influences the evolution of the ischaemic penumbra, the size of the core infarct and affects functional outcomes. The presence of good collateral vessels has been shown to promote recanalisation after acute large vessel occlusion and reduces the risk of haemorrhagic transformation by limiting local perfusion impairment 5,7,8. The paucity of good collateral vessels also correlates with a higher risk of treatment complications 7.
Overall, the poorer the collateral vessels in a region of ischaemia, the larger the core infarct (DWI lesion size 5) and the worse the clinical (functional) outcomes 3-5. Good leptomeningeal collateral vessels have been shown to correlate with lower baseline ASPECTS 3 and robust collateral vessels have been shown to be an independent predictor of final infarct volume 4.
Patients with poor collateral vessels have been termed fast progressors in whom infarct growth rate is quick compared to patients with strong collaterals, the slow progressors who are able to tolerate ischaemia longer without progressing to infarction 1.
Collateral scoring systems
Several scoring systems have been described in the literature 1, based either on single- or multiphase CT angiogram:
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