Common carotid artery occlusion is rare and accounts for only about 0.24–5% of stroke patients. In 2013, Bajkó et al. analysed 5000 cases who received ultrasound and CT angiography, of whom 160 (3.2%) had carotid artery occlusion (Bajkó et al. 2013). Of these 160 patients, 20 (0.4%) presented with CCA occlusion or CCA occlusion associated with ICA occlusion. In another large ultrasonographic study of 6412 cases reported by Parthenis et al., the prevalence of CCAO was 0.54% (Parthenis et al. 2008). In addition, a case series by Chang et al. in 1995 showed that CAAO was almost equally distributed in both sides (51% located on the left) (Chang et al. 1995), and Belkin et al. in 1993 reported similar results (41% on the right side) (Belkin et al. 1993). A higher incidence was found in the patients who received surgical revascularization with patent distal vessels of left-sided occlusion (Parthenis et al. 2008). A possible explanation is that symptoms may be more obvious when left-sided occlusion occurs in right hemisphere-dominant people.
Various etiologies of CCAO have been reported. The major cause of CCAO is atherosclerosis, accounting for up to 75% of cases, and the strongest risk factors are hypertension and heart disease (Bajkó et al. 2013; Chang et al. 1995). Other causes include post-irradiation arteriopathy, cardiac embolism, dissection, aortic arch aneurysm, hypercoagulability, fibromuscular dysplasia, and Takayasu’s arteritis, which has been reported to be more common in Asian patients. One retrospective study reviewed 42 patients with Takayasu’s arteritis, and found that the CCA was the second most commonly involved vessel (47.6%), followed by the subclavian artery (50%) (Park et al. 2015).
The clinical manifestations of CCAO are associated with a variety of neurological symptoms, ranging from asymptomatic to severe cerebrovascular events. In addition, Man and Fu reported that patients who received neck irradiation for nasopharyngeal carcinoma only presented with isolated oculomotor nerve palsy (Man and Fu 2013). Since there are limited data in the literature and some patients do not have any symptoms, the true incidence of CCAO may be underestimated.
Collateral circulation can originate extracranially from the ipsilateral subclavian artery or intracranially from the circle of Willis, providing perfusion to the ipsilateral cerebral hemisphere in CCAO. Bajkó et al. reported an association between a higher incidence of occluded distal vessels and poorer short-term outcomes, however only two cases underwent revascularization surgery (Bajkó et al. 2013).
Two classification systems have been proposed. The first is classified by carotid duplex imaging, and depends on the patency and flow direction of the distal carotid vessels. Type I indicates isolated occlusion of the CCA and patent distal vessels, with flow directed from the external to ICA as type Ia and from the internal to external carotid artery as type Ib. Type II indicates isolated patent external carotid artery and type III indicated isolated patent ICA. Both vessels occlusion is classified as type IV. In this classification system, the flow direction in the ophthalmic and anterior or posterior communicating cerebral arteries is either antegrade or retrograde. Retrograde flow in the ophthalmic artery is more often associated with types II and IV lesions. Moreover, contralateral ICA stenosis has also been reported to be more severe in patients with type II and IV lesions (Parthenis et al. 2008).
The second classification system, known as Rile’s classification, is most widely used. According to the angiographic findings, type 1A involves a patent ICA and ECA, type 1B a patent ECA and an occluded ICA, type 1C a patent ICA and an occluded ECA, and type 2 total CCA, ICA, ECA occlusion (Klonaris et al. 2013). In our two patients, they were Rile’s type 1B occlusion.
The indication for CCAO intervention remains controversial, and the treatment has not been standardized. Surgical revascularization is possible in cases of patent distal vessels (Bajkó et al. 2013). A review study conducted by Klonaris in 2013 included 21 published studies and a total of 146 patients who underwent revascularization procedures for CCAO from 1965 to 2012 (Klonaris et al. 2013). The vast majority of the patients were treated with a surgical bypass procedure, and other techniques included transposition of the CCA to the subclavian artery, and endarterectomy (10%), whereas an endovascular procedure was performed in only one patient (0.9%) (Klonaris et al. 2013). However, this small percentage of using an endovascular approach may be based on the limited knowledge of this technique. First, chronic atherosclerotic plaques in CCA are usually heavy and calcified, which may restrict the guidewire from crossing the lesions, especially when they comprise the entire length of the CCA. Second, procedural risks such as embolic stroke is also a consideration. Finally, the prevalence and incidence of CCAO is rare, so that experience of this therapeutic approach is limited.
In our patients, the symptoms varied from dizziness to upper extremity weakness. During the procedure, a common characteristic was the presence of some thrombus or debris, indicating that the pathophysiology may not have been only atherosclerosis but also thrombosis, which is compatible with previous studies. The symptoms all improved after CCA revascularization. Experience of internal carotid stenting has shown the benefit of revascularization of chronic total occlusion (Chen et al. 2016); however, the field of endovascular interventions for CCA is limited. Although surgery is currently still the gold standard of treatment, endovascular treatment is an alternative choice that can provide adequate distal protection and thrombosuction.
Of note, we found thrombus and debris within the CCA in both of our cases. The longer the occlusion time, the more fragmented white debris and black blood clots were noted. From our experience, we suggest that routine IVUS and thrombosuction should be performed for CCA total occlusion. Common carotid artery total occlusion is rare and with variable etiology. The treatment is challenging with an endovascular approach. Both of our cases were successfully treated with endovascular revascularization for common carotid artery total stenosis. Endovascular therapy may be an alternative treatment other than surgery. Further large clinical study for comparing the safety and efficiency in surgical and endovascular treatment may be required.