As an overall comment pertaining to dissection, treatment is primarily with anticoagulation or antiplatelet agents for several weeks or months and followed up with some form of arteriography. The choice between aspirin and warfarin has not been clarified as the rate of stroke is low, in the range of 5 percent or less, and remains so with either agent (Georgiadis and colleagues). If the dissection has produced complete occlusion of the vessel, the role of anticoagulation is less clear. Endovascular revascularization has been attempted with mixed results. Similarly, tandem lesions, meaning carotid dissection and a downstream intracranial embolus, have been treated with stenting and either thrombolysis of thrombectomy but again, the results are hard to judge.
An issue pertaining to treatment is in establishing the presence of dissection into the subarachnoid space of the intracranial compartment and the risk of subarachnoid hemorrhage. For carotid dissection, such extensions would seem to present a risk of subarachnoid hemorrhage if the lesion reaches beyond the cavernous sinus. Within the sinus, any bleeding would create a cavernous-carotid fistula, which is not usually fatal. In vertebral dissection, this question arises when the false lumen extends into the foramen magnum, beyond the dural entry of the vessel.
Although there are no data to determine the proper approach to acute treatment in these circumstances that entail a risk of a subarachnoid hemorrhage, in general we do use heparin and warfarin for a brief period, followed by aspirin, because of the greater concern for embolus, unless there is existing subarachnoid blood on a CT scan or if there is a pseudoaneurysm within the intracranial portion of the dissection (see Metso et al). Some stroke specialists have suggested that a lumbar puncture be performed before initiating anticoagulation but this has not usually been our practice.
Moyamoya is a Japanese word for a “haze,” “puff of smoke”; it has been used to refer to an extensive basal cerebral rete mirabile—a network of small anastomotic vessels at the base of the brain around and distal to the circle of Willis, seen in carotid arteriograms, associated with segmental stenosis or occlusion of the terminal intracranial parts of both internal carotid arteries (Fig. 33-21). This form of cerebrovascular disease is predominant in, but not limited to the Japanese. The authors have periodically observed such patients, as have others, in the United States, Western Europe, and Australia. Certain hemoglobinopathies, particularly sickle cell anemia, may cause a vasoocculsive condition equivalent to moyamoya disease, possibly because of sickling of red blood cells in the vasa vasorum of the supraclinoid carotid artery. An association between moyamoya, Down syndrome, and certain human leukocyte antigen (HLA) types favors a hereditary basis (Kitahara et al). A familial component has long been suspected but can be established in only 10 percent of cases, possibly in an autosomal dominant pattern with incomplete penetrance due to a site on chromosome 17q that has been implicated as one possible locus. Also, a rare condition in either Asians or Europeans of atherosclerotic occlusion of the distal intracranial carotid arteries can cause deep collateral vessels to enlarge and simulate moyamoya. In this way, moyamoya can be considered either a radiologic pattern or a disease process.