Carotid Artery Dissection 

Carotid artery dissection (CAD) begins as a tear in one of the carotid arteries of the neck, allowing blood under arterial pressure to enter the wall of the artery and split its layers. The result is either an intramural hematoma or aneurysmal dilatation, both of which can be sources of microemboli, with the latter also causing mass effect on surrounding structures.

Carotid artery dissection is a significant cause of ischemic stroke in all age groups, but it occurs most frequently in the fifth decade of life and accounts for a much larger percentage of strokes in young patients.^[1] Dissection of the internal carotid artery can occur intracranially or extracranially, with the latter being more frequent. Internal carotid artery dissection can be caused by major or minor trauma, or it can be spontaneous, in which case, genetic, familial, and/or heritable disorders are likely etiologies.

Although in practice dissections are labeled spontaneous in the absence of major blunt or penetrating trauma,^[2] when associated with minor mechanism trauma they may be caused or influenced by an underlying arteriopathy.^[3] Patients can present in a variety of settings, such as a trauma bay with multiple traumatic injuries; the physician's office with nonspecific head, neck, or face pain; or to the emergency department with a partial Horner syndrome.

Sophisticated imaging techniques, which have improved over the last 2 decades, are required to confirm the presence of dissection. Most ischemic cerebral symptoms arise from thromboembolic events; therefore, early institution of antithrombotic treatment provides the best outcome.^[4] Once diagnosed and treated, patients with carotid artery dissection (CAD) require regular follow-up and imaging studies of both carotids as healing usually takes 3-6 months and the incidence of contralateral dissection is higher than in the general population. When diagnosed early, prognosis is usually good. A high index of suspicion is required to make this difficult diagnosis.

Although the cause of internal carotid artery dissection remains elusive, mechanical forces (trauma, blunt injury, stretching) and underlying arteriopathies (Ehlers-Danlos syndrome IV, other connective tissue disorders/aberrations) alone, or in combination, account for most of the pathophysiology. It is widely accepted that carotid artery dissection (CAD) is a multifactorial disease.^[5]

Carotid artery dissection begins as a tear in the tunica intima or directly within the tunica media (possibly originating from the vasa vasorum).^[1] The blood dissects along the artery to create an intramural hematoma leading to a thrombus, which can narrow the carotid artery lumen and become a nidus for distal embolization.^[2] Sometimes, the dissection plane lies between the tunica media and tunica adventitia, resulting in an aneurysmal outpouching of the arterial wall that may also become a source of distal emboli. Aneurysmal dilatation can also cause mass effect on nearby structures such as sympathetic fibers and the lower cranial nerves.^{[1, 2]} The dilatation resulting from an internal carotid artery dissection may be termed a true, as opposed to a false, aneurysm because the wall is composed of blood vessel elements.

Frequency

United States

The annual incidence of symptomatic spontaneous internal carotid artery dissection ranges from 2.5-3 per 100,000.^[1] The incidence of carotid artery dissection as a result of blunt injury (mainly high-speed motor vehicle accidents) ranges from less than 1% to 3%.^[6] The actual incidence may be higher because some dissections are asymptomatic or cause only minor transient symptoms and remain undiagnosed.

Mortality/Morbidity

Spontaneous internal carotid artery dissection has a reported mortality rate of less than 5%, although the morbidity and mortality of internal carotid artery dissection due to blunt trauma may be much higher.

• Morbidity from carotid artery dissection varies in severity from transient focal deficits to permanent cerebral or retinal ischemic injury, and even death in the setting of trauma.
• Over half of patients with spontaneous carotid artery dissection develop stroke,^[1] although this may be delayed by hours or days.
• Rates of delayed stroke due to blunt-traumatic causes of carotid artery injury range from 3% in grade I injuries to 44% in grade IV injuries.^[2]
• In the setting of blunt trauma, 37-58% of patients have permanent neurologic deficit on discharge,^[6] although early use of antithrombotic therapy has essentially eliminated ischemic events in asymptomatic patients with carotid artery dissection.^{[4, 7]}
• As in other causes of stroke in young adults, the functional outcome is generally good, and recurrence of cerebral ischemia and carotid artery dissection is rare.^[5]

Sex

No gender-based difference exists for spontaneous internal carotid artery dissection, although there may be a slight male predominance when taking into account traumatic causes of carotid artery dissection.

Age

• Internal carotid artery dissection is a common cause of ischemic stroke in patients younger than 50 years and accounts for up to 25% of ischemic strokes in young and middle-aged patients.^[1]
• The mean age for ischemic stroke secondary to internal carotid artery dissection from blunt traumatic injury is even younger at 35-38 years old.
• Dissection of the intracranial part of the internal carotid artery is rare at any age because the intracranial carotid artery is less mobile and the skull absorbs most of the force of trauma.