Relationship between CT angiography-derived collateral status and CT perfusion-derived tissue viability

Highlights

• There is a quite good correlation between CTA collateral grades and CTP results.

• The mismatch defined with Tmax>6s and rCBF<30% best correlates with CTA collaterals.

• There is no significant correlation between onset time and mismatch ratio.

AIM

To explore the relationship between computed tomography (CT) angiography (CTA)-derived collateral status and CT perfusion (CTP)-derived tissue viability.

MATERIALS AND METHODS

Patients having middle cerebral artery (MCA) M1/M2 segment and/or internal carotid artery (ICA) occlusion and within 12 hours of onset were included. Collateral was graded from 0 to 3 on maximum intensity projection (MIP) images of CTA. The area with relative cerebral blood flow (rCBF) <30% or time-to-maximum (Tmax) >10 or >12 or >14 seconds was defined as the infarct core, and Tmax >6 seconds as the penumbra. Kruskal–Wallis and Spearman's correlation tests were performed to assess the correlation between collateral grade and infarct size or mismatch ratio.

RESULTS

Eighty-three patients were enrolled and 52 of them met the inclusion criteria. Infarct size defined by rCBF <30% or Tmax >10 or >12 or >14 seconds and mismatch ratios were significantly different among the four groups. The correlation between collateral grades and infarct core using rCBF <30% (ρ=–0.814, p<0.01) was better than that defined by Tmax >10s, >12s or >14s. Mismatch ratio for the infarct core defined by rCBF <30% (ρ=0.945, p<0.01) had the best correlation with collateral grades.

CONCLUSION

Patients with good collaterals show a smaller infarct core and higher mismatch ratio. Infarct size defined by rCBF <30% and mismatch ratio defined by rCBF <30% and Tmax >6 seconds appear to be more correlated with collaterals in AIS patients.

Introduction

The cerebral collateral circulation plays an important role to reconstruct blood supply to ischaemic brain tissue. When a localised major blood vessel is blocked, the contralateral blood flow through the circle of Willis carries blood around the blockages, and anastomosis with smaller vessels will open up.¹ The collateral supply improves the success rate of vascular recanalisation therapy and reduces the infarct volume and the risk of haemorrhagic transformation.

The grading of collateral vessels on computed tomography (CT) angiography (CTA) makes the selection of patients for intra-arterial treatment (IAT) more effective.² The Endovascular Treatment for Small Core and Anterior Circulation Proximal Occlusion With Emphasis on Minimising CT to Recanalisation Times (ESCAPE) trial demonstrated that endovascular treatment was more effective in patients with moderate to good collaterals on CTA.³ CT perfusion (CTP) mismatch predicts penumbra and infarct core intuitively and accurately. The Extending the Time for Thrombolysis in Emergency Neurological Deficits–Intra-Arterial (EXTEND-IA) trial used CTP to screen patients for early endovascular therapy.⁴ A comprehensive understanding of CTA and CTP information in acute settings may facilitate the triage of acute ischaemic stroke (AIS) patients who may still benefit from intra-arterial treatment, such as mechanical thrombectomy, beyond 4.5 hours.

The objective of the present study was to determine whether CTA-derived collateral status and CTP-derived tissue viability could provide correlative and effective ischaemic information for clinical mechanical thrombectomy or thrombolysis. An additional aim was to explore which CTP parameters defined infarct core and penumbra better associated with their collateral status.