Dissection Syndromes 

Dissection occurs when blood extrudes into the connective tissue framework of a vessel wall, causing separation of the natural vessel layers. Dissection of the cervical and intracranial vessels is an uncommon but increasingly recognized condition.

The cervical (extracranial) internal carotid artery is affected in 75% of patients (usually approximately 2 cm distal to the bifurcation) and the extracranial vertebral artery in 15% of patients. The remaining cases usually involve the intracranial internal carotid artery, intracranial vertebral artery, middle cerebral artery, or basilar artery. Cervicocephalic dissections may occur spontaneously or secondary to major or minor trauma. In some patients, they are associated with an underlying arteriopathy. Fifteen percent of cases are bilateral, and one half of these occur in patients with underlying fibromuscular dysplasia.

The hallmark of dissection is hemorrhage within the vessel wall. In some patients, an intimal tear allows intravascular blood to communicate directly with the vessel wall cavity. In others, an intramural hematoma develops without a direct connection with the vessel lumen.

In extracranial carotid and vertebral dissections, hemorrhage into the medial-adventitial layers occurs most commonly. This occasionally causes the external vessel wall to bulge outward, forming a dissecting aneurysm that can compress local structures. In intracranial carotid and vertebral dissections, subintimal tears occur more commonly, leading to formation of intramural hematomas that protrude inward and narrow the vessel lumen. Most ischemic symptoms (85-95%) are caused by emboli from the site of the dissection, while the remainder are due to vessel narrowing with hemodynamic insufficiency (5-15%).

Frequency

United States

Hospital-based series suggest that cervicocephalic dissections are responsible for 1-2.5% of ischemic strokes in the general population and for 5-20% of strokes in individuals younger than 45 years. In one community-based study, the average annual incidence of spontaneous cervical internal carotid artery dissections was 2.6 cases per 100,000. While improved imaging techniques and growing awareness of the disorder have led to increased recognition of these syndromes, mild cases likely will remain undiagnosed.

International

International frequency of dissection syndromes is similar to that in the United States.

Mortality/Morbidity

Morbidity and mortality of cervicocephalic dissections vary according to the vessel and location of the dissection. Death rates for extracranial carotid and vertebral dissections are approximately 5-10%. In contrast, mortality rates for intracranial carotid and basilar dissections approach 70% or higher.

Race

No racial preponderance is demonstrated.

Sex

While males and females are affected equally in extracranial carotid dissections, intracranial dissections are more common in younger males than in females. Extracranial vertebral artery dissections and multiple vessel dissections are more common in women than in men.

Age

Persons of all ages may be affected; however, dissections occur more frequently in younger individuals. In extracranial carotid dissection, 70% of cases occur in persons aged 35-50 years. Intracranial carotid dissection tends to occur particularly in adolescents and adults younger than 30 years.