Atherosclerosis and aortic inflammation are known to be the most common causes of bilateral carotid artery occlusion without moyamoya disease.
17) Atherosclerosis can occur at the point of ICA bifurcation, leading to chronic and progressive arterial stenosis, whereas aortic inflammation is likely to be involved with the aortic arch and its branches, resulting in bilateral carotid artery occlusion. Generally, an occlusion at the beginning part of the ICA is likely to be caused by atherosclerosis, while the occlusion of the bilateral common carotid artery is likely aortitis.
17) According to the study by AbuRahma and Copeland,
1) all patients with atherosclerotic bilateral ICA occlusion had a history of cerebral ischemic attack such as transient ischemic attack (TIA), amaurosis fugax, or stroke even though collateral circulation was present, and they all needed surgical interventions such as endarterectomy, carotid-subclavian bypass or medical treatments using warfarin or aspirin.
By contrast, definite cases of moyamoya disease are diagnosed in patients with bilateral stenosis or occlusion that occurs at the terminal portion of the ICA together with an abnormal vascular network at the base of the brain, as is shown by cerebral angiography. The etiology of moyamoya disease is unknown. Thus, moyamoya syndromes that have underlying diseases such as cerebrovascular disease with atherosclerosis, autoimmune disease, meningitis, brain neoplasm, Down's syndrome, neurofibromatosis, head trauma or irradiation to the head, as well as other conditions, should be excluded.
9)Meanwhile, our case showed complete occlusion at the bilateral proximal portion of the internal carotid arteries above the carotid bulbs with abnormal vascular networks from the posterior circulation without basal moyamoya vessels. The patient did not have any underlying diseases such as cerebral infection, trauma and aortic inflammation that may lead to stenosis or occlusion of the ICA. Although he had no past history of TIA, he had two risk factors for atherosclerosis which were hypertension and smoking. No abnormal findings that may imply fibromuscular dysplasia were seen on the vertebral and abdominal angiograms. These findings are not characteristics of moyamoya disease or moyamoya syndrome, but suggest idiopathic or atherosclerotic bilateral carotid artery occlusion.
The basilar tip aneurysm associated with bilateral carotid artery occlusion or moyamoya disease is well known, life-threatening complication that causes SAH. To the best of our knowledge, there have been only seven cases of bilateral carotid artery occlusion with concurrent basilar tip aneurysm without moyamoya disease in the literature.
5),
7),
8),
11),
12),
17),
18) The causes of carotid artery occlusion included aortic inflammation in two cases and atherosclerosis in five cases.
5),
7),
8),
11),
12),
17),
18) Of them, 5 cases had SAH.
8),
11),
12),
17),
18) It has been suggested that increased blood flow through the vertebrobasilar system, which is the major source of collateral circulation in bilateral carotid artery occlusion, intensifies the hemodynamic stress on the arterial walls and this may result in the formation of saccular aneurysms.
13) Although the formation of anastomosis from the external carotid artery may alleviate the hemodynamic burden on the posterior circulation, the effect is limited and local blood pressure still rises which leads to the risk of basilar artery aneurysms.
17) Conservative management for these aneurysms can lead to dismal results,
11),
18) therefore quick, aggressive treatments should be considered. Such aneurysms can be treated with direct clipping. However, direct clipping is difficult and dangerous due to extensive collateral channels,
2),
14) stiffness of the carotid artery,
10),
16) and high internal blood pressure.
7) Moreover, the fact that the basilar artery is the sole source of blood for most of the brain precludes prolonged temporary clipping to aid in safe dissection around the aneurysm.
13) Thus, these aneurysms have been recently treated with endovascular procedures using soft platinum coils. There have been several reports have showing excellent results of endovascular embolization for the basilar tip aneurysms in patients with moyamoya disease and bilateral ICA occlusion.
4),
6),
7),
10),
12),
17) Of course, if increased blood burden through the vertebrobasilar system is not alleviated, the aneurysm will probably regrow. Thus, in our case, regular follow-up angiograms are essential and additional embolization with extra-intracranial revascularization may be needed even though there was no perfusion defect seen on the perfusion CT scans.
1 Nam-Jun Lee, MD, PhD,2 Shin-Hyuk Kang, MD, PhD,1 Dong-Jun Lim, MD, PhD,3 and Yong-Gu Chung, MD, PhD1
