Accuracy of Distal Internal Carotid Artery Contrast Ratio to Infer Proximal Carotid Disease in the Mobile Stroke Unit.

BACKGROUND

Extracranial internal carotid artery (ICA) stenosis is a common cause of ischemic stroke and transient ischemic attack. Cervical computed tomography (CT) angiography can rapidly diagnose carotid pathology but is not possible with current-generation CT scanners used in mobile stroke units. We assessed the diagnostic accuracy of the intracranial ICA contrast density ratio (CDR) to identify extracranial ICA stenosis.

METHODS

We retrospectively reviewed consecutive patients at 3 comprehensive stroke centers in Melbourne, Victoria, who received CT angiography on the mobile stroke unit CereTom CT scanner, with reference standard in-hospital CT angiography or digital subtraction angiography in the Melbourne mobile stroke unit database. The mean Hounsfield units at 4 segments of the intracranial ICA, both ipsilateral and contralateral to the symptomatic hemisphere, were measured. The CDR was calculated using the formula: CDR=contralateral mean Hounsfield units/ipsilateral Hounsfield units. Statistical analysis was completed with univariate analysis of CDR, and leave-one-out cross-validation with receiver operating characteristic area under the curve to determine CDR thresholds associated with stenosis or occlusion, to determine sensitivity and specificity of the test.

RESULTS

Of 151 patients included, 31 of 151 (20.5%) had extracranial ICA stenosis >50%, and the average CDR was higher in patients with >70% stenosis with threshold ratio of >1.24 (sensitivity, 80%; specificity, 88%; positive predictive value, 57%; and negative predictive value, 96%) or extracranial occlusion (sensitivity, 100; specificity, 82%; positive predictive value, 29%; and negative predictive value, 100%). The threshold of 1.18 for 50% to 99% and carotid occlusion had lower sensitivity (sensitivity, 78%; specificity, 95%; positive predictive value, 88%; and negative predictive value, 91%).

CONCLUSIONS

Assessment of the intracranial ICA CDR may assist in ruling out high-grade extracranial stenosis in patients who are being considered for direct transfer for endovascular thrombectomy after head-only CT angiography.