Differentiating pseudo-occlusion from true occlusion of proximal internal carotid artery in acute ischemic stroke on CT angiography

Objective: A lack of visualization of the proximal internal carotid artery (ICA) on computed tomography angiography (CTA) in acute ischemic stroke may be caused by an atherosclerotic occlusion or a pseudo-occlusion by a massive thrombus in the ICA. Pseudo-occlusion of the proximal ICA is caused by stagnant flow from a distal ICA occlusion. The purpose of this study aimed to use imaging findings of CTA to differentiate pseudo-occlusions from true occlusions of the proximal ICA. Patients and methods: All eligible patients undergoing endovascular treatment after CTA from January 2013 to March 2018 were respectively reviewed. Patients with <2 cm of ICA on CTA images were enrolled in this study. CTA images were classified as having a beak, dome, or flat pattern. Results: Our sample included a total of 66 eligible patients (true occlusion: 31, pseudo-occlusion: 35). The total length of opacification of the proximal ICA in the pseudo-occlusion group was significantly higher compared to that in the true occlusion group (13.9 ± 4.0 vs. 6.1 ± 4.8, p < 0.001). A beak pattern of the proximal ICA on CTA images was significantly higher in the pseudo-occlusion group (82.9% vs. 16.1%, p < 0.001), but a flat pattern was significantly higher in the true occlusion group (58.1% vs. 0%, p < 0.001). Gradual contrast decline of the proximal ICA on CTA images only appeared in the pseudo-occlusion group (51.4%, p < 0.001). Conclusions: On CTA, imaging patterns of the proximal ICA can be differentiated between true occlusions and pseudo-occlusions.