The annual incidence of spontaneous carotid artery dissection ranges from 2.5 to 3 per 100,000 (43); between 0.5 and 2.5 cases of vertebral dissection per year are reported from large referral-based hospitals (1,14,36, 37,43). The overall frequency of head pain is extremely high, ranging from 60 to 95% in carotid artery dissections (1,4,6,14, 15, 16,34,35,37,43,47) and around 70% in vertebral artery dissections (15,34, 35, 36,43,47). Pain is the most frequent inaugural symptom of both carotid and vertebral dissections (1,3,4,6,7,9,14, 15, 16, 17,20,27,30, 34, 35, 36, 37,42,43,47,48,52), potentially leading to recognition of the condition before the occurrence of ischemic signs.

Patients with a spontaneous dissection of the carotid or vertebral artery are thought to have an underlying structural defect of the arterial wall, although the exact type of arteriopathy remains elusive in most cases (19,21, 22, 23,43,53). Ehlers-Danlos syndrome type IV, Marfan syndrome, autosomal dominant polycystic kidney disease, and osteogenesis imperfecta type I have been identified in 1 to 5% of patients with spontaneous dissections of the carotid or vertebral artery (21,43). In addition, approximately 5% of patients with a spontaneous dissection of the carotid or vertebral artery have at least one family member who has had a spontaneous dissection of the aorta or its main branches, including the carotid and vertebral arteries. In some of these families, there is also a history of multiple cutaneous lentigines or a congenitally bicuspid aortic valve (21,23,43). The arterial media of the aorta and its branches, melanocytes, and the aortic valvular cusps are all derived from neural-crest cells, suggesting that the underlying defect in these families is an abnormality of neural-crest cells. Angiographic changes of fibromuscular dysplasia are found in about 15% of patients with a spontaneous dissection of cervical arteries, and cystic medial necrosis is a common finding at postmortem examination (21,43). In addition, indirect evidence of a generalized arteriopathy is suggested by the association of such spontaneous dissections with intracranial aneurysms, a widened aortic root, arterial redundancies (e.g., coils, kinks, and loops), and increased arterial distensibility (21,22,43,53). Finally, ultrastructural abnormalities of dermal connective tissue components have been detected in up to two thirds of patients with a spontaneous dissection of the carotid or vertebral artery (23).

Dissections of the carotid and vertebral arteries usually arise from an intimal tear. The tear allows blood under
arterial pressure to enter the wall of the artery and form an intramural hematoma, the so-called false lumen. The intramural hematoma is located within the layers of the tunica media, but it may be eccentric, either toward the intima or toward the adventitia. A subintimal dissection tends to result in stenosis of the arterial lumen, whereas a subadventitial dissection may cause aneurysmal dilation of the artery (43).

The cause of cervical cerebral arterial dissection remains largely unknown. It is often classified as spontaneous or traumatic. A history of a minor precipitating event is frequently elicited in patients with a spontaneous dissection of the carotid or vertebral artery. Neck movements, particularly when they are sudden, may injure the artery as a result of mechanical stretching. Chiropractic manipulation of the neck has been associated with carotid and vertebral artery dissection (43). A recent history of a respiratory tract infection is also a risk factor for spontaneous dissections of the carotid or vertebral artery (19). Two case-control studies suggested migraine as a risk factor for dissection (11,51).

The pain of cervical arterial dissections is a referred pain to the face, head, and neck originating from the dissected artery. In carotid artery dissection, the pain is referred to ipsilateral cephalic and facial regions, the location of which follows the patterns outlined during electric stimulation of the carotid bifurcation or during balloon inflation in the distal carotid artery (4,16,47). In vertebral artery dissection, the location of pain at the posterior neck and also to anterior head regions is likely to be explained on the basis of innervation of these arteries by the upper cervical roots and the convergence of those with descending trigeminal impulses (3,21,30). The pain mechanisms remain largely undetermined. Proposed potential mechanisms include mechanical stimulation of the pain-sensitive receptors in the vessel wall as a result of dilation or distention of the artery and ischemia of the perivascular pain-sensitive nerve fibers resulting from direct mechanical injury and occlusion of the vasa nervorum. The variability of the observed head pain patterns, including whether it occurs, the various localizations, the different degrees of severity, and the different pain qualities, are not explained adequately by any of the proposed mechanisms (3,4,7,9, 15, 16, 17,20,21,27,30,42,43,47,48,52).

The IHS diagnostic criteria (Revised International Classification of Headache Disorders [ICHD-II]) for headache in cervical arterial dissection are as follows:

A. Any new headache or facial pain of acute onset with or without neurologic symptoms or signs.

B. Dissection demonstrated by appropriate vascular and neuroimaging investigations.

C. Headache occurs in close temporal relation to and on the same side as dissection.

D. Disappearance of pain within 1 month.