Good collateral circulation (CC) is a strong outcome predictor in acute stroke patients. CT angiography (CTA) is wide-world available but does not provide accurate information about parenchymal status. CT perfusion (CTP) is frequently used to determine ischemic core and tissue at risk. Our aim was to identify an easy and quick method to evaluate CC status by CTP.
Methods: Consecutive ischemic stroke patients <8h from symptoms onset evaluated for reperfusion therapies were studied. Non-contrast CT, CTP and multiphase CTA were performed. Patients with confirmed M1-MCA or TICA occlusion on CTA were included. CC evaluation was determined by multiphase CTA (mCTA) according to the Calgary CC Scale and classified as poor (grades 0-2) or good (grades 3-5). In CTP maps, one single ipsi- and contralateral regions of interest (ROI) were defined in the MCA cortical territory (M4, M5, M6). We studied the association of absolute and relative to contralateral ROI-CTP values with CC degree determined by mCTA.
Results: 33 patients were included, median NIHSS 17.5 (2-22). Twenty-five patients (75.8%) presented a M1 and 8 (24.2%) a TICA occlusion. On mCTA, 27 (81.8%) patients presented with a favourable CC status and 6 (18.2%) with poor CC. Mean ROI values in the ischemic MCA territory were: CBV 3.5±1.5 ml/100mg, CBF 46.9±29.3 ml/100mg/min, MTT 8.1±3.1 s, Tmax 23.2±4.4 s. In the contralateral non-ischemic MCA, the mean ROI values were: CBV 3.48±1.4, CBF 66.5±32.7, MTT 5.6±2.3, Tmax 20.4±4.8. Absolute and relative CBV-ROI data (relCBV= ischemic CBV value / contralateral CBV value) were the only values significantly associated with CC status on mCTA (good CC mean CBV: 3.8 ml/100g VS poor CC mean CBV: 1.9, p=0.006; good CC mean relCBV 1.1 vs poor CC mean relCBV 0.6, p=0.019). A ROC curve defined 2.5 ml/100mg as the better cut-off point of ROI-CBV that identified patients with good CC status (sensitivity 96%, specificity 84%, VPP 0.96, VPN 0.83). Patients with a ROI-CBV >2.5 presented lower median NIHSS after 24 hours (4 vs 18, p= 0.012) and smaller mean infarct volume on control CT (27.9 vs 88.3, p=0.021).
Conclusion: A single cortical ROI-CBV allows an easy and quick accurate evaluation of collateral circulation in CTP. ROI-CBV>2.5 ml/100mg is related to good clinical and radiological outcomes.