Validation of Ultrasound Parameters to Assess Collateral Flow via Ophthalmic Artery in Internal Carotid Artery Occlusion

This study aimed to characterize the flow patterns using ultrasound (US) in the external carotid artery (ECA) in patients with total occlusion of internal carotid artery (ICA) and characterize collateral retrograde flow through the ophthalmic artery (OA, secondary collateral, internalization). This study was performed on 45 patients who were retrospectively selected with total occlusion of the ICA, who underwent digital subtraction angiography (DSA), magnetic resonance angiography (MRA), and US (43 men; mean age 68.1 ± 7.9 years). Collateral retrograde flow and collateral flow through the circle of Willis (primary collateral) were determined by DSA and MRA. We compared several US parameters such as ECA peak systolic velocity, mean velocity, end-diastolic (ED) velocity, pulsatility index (PI), and pulsatility transmission index (PTI). PTI was defined as the ratio of ipsilateral ECA PI to the ipsilateral common carotid artery (CCA). In this patient group, 27 patients showed retrograde flow through OA as assessed by DSA. The presence of primary collateral flow was significantly lower in patients with retrograde flow than without (P < .05). ECA ED velocity was significantly higher, and PI and PTI were significantly lower with retrograde flow through OA than without (P < .05). According to receiver operating characteristic analysis, PTI was the most highly correlated ultrasonologic parameter with internalization (cutoff value, .94; sensitivity, 92.6%; specificity, 94.5%). Using PTI was discriminative to determine internalization of ECA because a collateral pathway through OA in cases of ICA occlusion had less primary collateral pathways.