Introduction: Extracranial internal carotid artery (ICA) stenosis is a common cause of ischemic stroke and transient ischemic attack. Cervical CT-angiography can rapidly diagnose carotid pathology but is not possible with portable CT-scanners used in Mobile Stroke Units (MSU). We assessed intracranial ICA contrast density (CD) as a marker of hemodynamically significant extracranial ICA stenosis.
Methods: We retrospectively reviewed patients at 3 comprehensive stroke centres in Melbourne, Victoria, who received CT-angiography on the MSU Ceretom CT-scanner, with or without in-hospital cervical CT-angiography. The CD was assessed as the mean Hounsfield units at 4 segments of the intracranial ICA, both ipsilateral and contralateral to the symptomatic hemisphere. A Contrast Density Ratio (CDR) was calculated using formula CDR = Contralateral CD / Ipsilateral CD. Statistical analysis was completed with univariate analysis of CD and CDR, and receiver operating characteristic (ROC) area-under-the-curve (AUC) to determine CDR thresholds associated with stenosis or occlusion, with positive (PPV) and negative predictive values (NPV).
Results: Of 224 patients included, the average CDR was higher in patients with 70-99% stenosis ratio>1.24 (ROC AUC 0.90, sensitivity 1.00 and specificity 0.88, PPV 0.3, NPV 1.0) or extracranial occlusion ratio>1.25 (ROC AUC 0.92, sensitivity 1.00 and specificity 0.85, PPV 0.4, NPV 1.0). The thresholds for 50-99% and 50-70% stenosis were less discriminating with ROC AUC 0.77 and 0.66 respectively.
Conclusion: Assessment of the intracranial ICA contrast density ratio may assist in ruling-out high-grade extra-cranial stenosis in patients who are being considered for direct transfer for endovascular thrombectomy after head-only CT angiography.