This woman had a dissection of her intracranial internal carotid artery (ICA). Spontaneous dissecting aneurysms of the intracranial carotid system are uncommon in adults, especially when compared with those of the vertebrobasilar system. Intracranial ICA dissection has been associated with fibromuscular dysplasia, cystic medial necrosis, intimal fibroelastic abnormalities, and atherosclerosis. In most patients, no microscopic pathologic changes are noted. The relationship between migraine and intracranial ICA dissection is unclear. One report described a 27-year-old woman who had a long history of migraine, who developed a spontaneous MCA dissection during a migraine attack. Edema of the involved vessels wall during the migraine was posited to provoke the development of the intracranial artery dissection. In another report, 3 of 10 patients with intracranial ICA dissections had long histories of migraine, but all of them reported that the headaches preceding the onset of their ischemic symptoms were more severe than their usual migraines and involved predominantly the retro-orbital, frontal, and/or temporal regions. These locations are frequent sites of referred pain described during stimulation of the distal portion of the ICA and MCA.
Neurological symptoms and signs usually follow almost immediately after the onset of the headaches. This finding differs from that usually seen in patients with ICA dissections in the neck, in which initial pain and headache symptoms often precede the brain ischemic symptoms by several days. Patients with extracranial ICA dissections may have headaches, Horner's syndrome, pulsatile tinnitus, and/or abnormalities of function of the lower cranial nerves without cerebral ischemia (as in case 5). Patients with intracranial ICA dissection almost invariably develop brain ischemia and cerebral infarcts. Fluctuation of neurological signs during the first 2 weeks after symptom onset is common in patients with intracranial ICA dissections and is explained by either intra-arterial embolism or changes in collateral flow due to hemodynamic factors. Cerebral hypoperfusion is the mechanism of many of these events, in contrast to distal embolism, which is considered to be the most important mechanism of cerebral ischemia in patients with extracranial ICA dissections. Past reports of patients with intracranial dissections were mostly necropsy, and they emphasized that most resultant brain infarcts were large and often fatal. More recent reports of patients diagnosed by brain and vascular imaging show that the size of infarcts varies widely and some are small and not disabling. In our patient, the dissection extended to the proximal MCA and diminished blood flow in the lenticulo-striate arteries, causing a striatocapsular infarct.
The typical angiographic findings of intracranial ICA dissection are the same as those observed with neck ICA dissections. String sign, double lumen, irregular scalloped stenosis, and vessel occlusion are found when the dissection involves the subintimal and intramedial layers, and aneurysm formation occurs when the subadventitial layer is affected. The most common intracranial site for aneurysm is the supraclinoid segment of the ICA with occasional extension into the MCA and/or the anterior cerebral artery (ACA).
Subarachnoid hemorrhage and aneurysm formation with mass effect are common complications in patients with intracranial ICA dissections but rare in patients with dissection of the extracranial vessels. The presence of thinner medial and adventitial layers and the lack of a well-developed external elastic lamina in the intracranial arteries have been implicated as the main factors causing subarachnoid hemorrhage in these patients. Most of the cases reported to date have involved the vertebrobasilar arteries, with a few reports describing subarachnoid hemorrhage in patients with dissection of the ACA or MCA. The reason for this discrepancy is unknown.
Some patients with intracranial ICA dissections are misdiagnosed as having vasculitis and are treated with steroids. The diagnosis of vasculitis is often offered by neuroradiologists and is wrong in over 95% of instances of stroke. Among all types of vasculitis with central nervous system involvement, the only one known to affect the distal portions of the ICAs is giant cell (temporal) arteritis. In most temporal arteritis patients that have intrac-ranial involvement, only the petrous and cavernous segments of the ICA are affected, with no involvement of the supraclinoid portion. Giant cell arteritis generally affects a much older population and is associated with an increased erythrocyte sedimentation rate and C reactive protein.
The treatment of patients with intracranial ICA dissection is controversial. Some favor anticoagulation to prevent propagation and embolization of thrombi and cite progression of neurological signs and brain infarction in patients who were not given anticoagulants. Others who argue against using anticoagulants worry about promoting hemorrhagic transformation of infarcts, progression of intramural vascular bleeding, and the development of subarachnoid bleeding during treatment with heparin. In our experience and that of others, patients with intracranial dissections present with either brain ischemia or subarachnoid hemorrhage. Patients who present with ischemic symptoms do not develop subarachnoid bleeding. Patients who present with subarachnoid hemorrhage that have been reported almost invariably have been treated neurosurgically or by instrumentation so that the natural history is unknown. Some probably could develop brain ischemia due to vasoconstriction.
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