Track Sign Distal to Internal Carotid Artery Occlusion

A 56-year-old man with a history of smoking presented transient motor aphasia 1 week prior. Neurological examination and non-contrast brain computed tomography (CT) were unremarkable. Carotid artery ultrasound demonstrated a severe stenotic plaque at the left internal carotid artery (ICA) bulb, with a low pulsatile distal blood flow. Digital subtraction angiography displayed a total occlusion at the ICA bulb at the early arterial phase. A retrograde blood flow reached the carotid bulb through a vessel collateralized with the external carotid artery (ECA) at the pharyngeal region. Next, having a U-type turn, it became a slow antegrade blood flow into the distal ICA. The two arteries with opposing flow directions paralleling at the cervical region created a track sign at the late arterial phase (Fig 1 and Video S1). The collateral artery was the ascending pharyngeal artery, usually arising from ECA, with an aberrant origin from the ICA bulb. This anomaly provides a rare collateral pathway via the ECA to the distal ICA in the proximal ICA occlusion. The patient's CT perfusion indicated a severe hypoperfusion of the left hemisphere. Carotid endarterectomy was recommended for him in the prevention of the risk of ischemic stroke. The patient underwent carotid endarterectomy successfully, and the lesion was confirmed to be atherosclerotic. He remained asymptomatic post-operatively. Symptomatic ICA occlusion carries a high early recurrence risk, up to 8% in the first month.1 Collateral status is pivotal in risk stratification, and their effectiveness varies depending on anatomical variations or whether there is a robust flow. Several collateral pathways compensate for reduced perfusion in ICA occlusion.2, 3 First-line compensatory routes involve the Circle of Willis, through the anterior or posterior communicating arteries. Secondary collateral pathways are ECA-ICA anastomoses, which are the ECA branches (eg, internal maxillary, ascending pharyngeal, or facial arteries) to the ICA via the vidian artery, the inferolateral trunk, or the ophthalmic artery. There are also leptomeningeal collaterals (pial arteries) in some cases. Ascending pharyngeal artery typically arises from the medial (deep) aspect of the proximal segment of the ECA, near the carotid bifurcation. If it is a collateral pathway when proximal ICA occlusion occurs, the blood flow into it is antegrade. On the contrary, if an aberrant ascending pharyngeal artery arising from ICA (approximately 1–3% of cases) plays a role in the collateral pathway, the blood flow into it is retrograde.4 In the present case, the course of the aberrant ascending pharyngeal artery was alongside the proximal ICA. Because of its long routine, the blood flow was slow, so the track sign distal to the occlusion was observed at the late artery phrase at the cervical region. None. Y.Y. and N.M. contributed to study concept and design; Y.Y. and J.Y. contributed to data acquisition and analysis; Y.Y., J.Y., and N.M. contributed to drafting the manuscript or preparing figures. Nothing to report. Obtained. Video S1. Track sign distal to internal carotid artery occlusion. Digital subtraction angiography showing total occlusion at the left internal carotid artery (ICA). Retrograde blood flow reached the carotid bulb via a collateral vessel originating from the external carotid artery at the pharyngeal region (circle). The flow then formed a U-shaped turn, transitioning into slow antegrade blood flow into the distal ICA (black arrows). The two arteries with opposing flow directions paralleling at the cervical region created a track sign at the late arterial phase. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.