The narrowed arterial segments show degeneration of elastic tissue and irregular arrays of fibrous and smooth muscle tissue in a mucous ground substance. Interspersed dilatations are a result of atrophy of the coat of the vessel wall. There is atherosclerosis in some and small degrees of arterial dissection in others. Usually vascular occlusion is not present, though there may be marked stenosis. Schievink and colleagues have summarized the pathology of this disease. In some instances the mechanism of the cerebral ischemic lesion is unexplained, but is presumed to be from small thrombi in the pouches or in relation to intraluminal septa.
The disease is not amenable to endarterectomy. So and colleagues have recommended excision of the affected segments of the carotid artery if ischemic neurologic symptoms are related to them, and conservative therapy if the fibromuscular dysplasia is an incidental and asymptomatic arteriographic finding. It is now possible to dilate the affected vessel by means of endovascular techniques and several case reports have suggested that benefit is achieved at lower risk than with surgical excision. Intracranial saccular aneurysms, which may accompany this disease as noted above, should be sought by arteriography, CT, or MRA and obliterated if their size warrants. It is not known if anticoagulation or antiplatelet therapy confers protection from stroke but the latter is often implemented.
Dissection of the Cervical and Intracranial Arteries
It has long been appreciated that the process formerly known as Erdheim medionecrosis aortica cystica, the main cause of aortic dissection, may independently involve or extend into the common carotid arteries, occluding them and causing massive infarction of the cerebral hemispheres. Examples of such occurrences were cited by Weisman and Adams in 1944 in their study of the neurology of dissecting aneurysms of the aorta, and Chase and colleagues gave the clinicopathologic details of 16 cases they studied. The principal neurologic features in both series were syncope, hemiparesis, or coma. The frequency of cerebral stroke with aortic dissection has varied from 10 to 50 percent and that of spinal stroke has been approximately 10 percent (see Chap. 44).
In more recent years, more attention has been drawn to the occurrence of spontaneous or traumatic dissection of the internal carotid artery, not necessarily associated intrinsic disease of the vessel walls, as an important cause of nonatherosclerotic stroke in young adults. Many large series of such cases have been reported in separate studies by Ojemann and colleagues (1972) and by Mokri and coworkers (1986 and 1988). Although the disease is overrepresented in women, it occurs frequently in men, typically in their late thirties or early forties for either sex. It is a spontaneous event or arises in relation to a whiplash injury, bouts of violent coughing, or direct trauma to the head or neck, which need not be severe—for example, being struck in the neck by a golf or tennis ball. We have encountered cases that occurred during pregnancy and immediately after delivery. Indeed, it is questionable if most cervical arterial dissections are truly “spontaneous,” as many can be connected to some strenuous event but a relation to trauma is often only presumed. Three of our patients over the years had a carotid dissection that was manifest as a hemiplegia days after blunt head injury that did not involve the neck.