Carotid artery dissection

Carotid artery dissection is a separation of the layers of the artery wall in the carotid arteries supplying oxygen-bearing blood to the head. It is the most common cause of stroke in younger adults. The term 'cervical artery dissection' should also be considered in the context of this article.

The carotid arteries are a pair of large bore arteries in the neck, they further divide into smaller vessels, the external and internal carotids on both the right and left side of the head/neck. Carotid arterial dissections occur when a tear or rip in the layers of the carotid arterial wall allows blood to flow between the layers of the artery. Artery dissection is not unique to the carotid artery system and can happen in numerous arteries in the body.

Blood within the walls of a dissected artery can compromise the flow of blood, leading to a slowing of oxygenated blood flow to the brain, complete blockage, or clot creation inducing a full blown stroke.

Dissection may occur after direct physical trauma, traffic collision, strangulation, or any phenomenon that causes hyperextension of the neck. They can also happen spontaneously.

Signs and symptoms
The signs and symptoms of carotid artery dissection may be divided into ischemic and non-ischemic categories:

Non-ischemic signs and symptoms:
 * Neck pain and headache, sometimes escalating in intensity
 * Decreased pupil size with drooping of the upper eyelid (Horner syndrome)
 * Pulsatile tinnitus

Ischemic signs and symptoms:
 * Temporary vision loss
 * Ischemic stroke

Causes
The causes of carotid artery dissection can be broadly categorized into two classes: spontaneous or traumatic.

Spontaneous
Once considered uncommon, spontaneous carotid artery dissection is an increasingly recognized cause of stroke that preferentially affects the middle-aged.

The incidence of spontaneous carotid artery dissection is low, and incidence rates for internal carotid artery dissection have been reported to be around 2.6 to 2.9 incidents per 100,000. Though the incidence is low, it is the cause of the vast majority of strokes in young people.

Observational studies and case reports published since the early 1980s show that patients with spontaneous internal carotid artery dissection may also have a history of stroke in their family and/or hereditary connective tissue disorders, such as Marfan syndrome, Ehlers-Danlos syndrome, autosomal dominant polycystic kidney disease, pseudoxanthoma elasticum, fibromuscular dysplasia, and osteogenesis imperfecta type I. IgG4-related disease involving the carotid artery has also been observed as a cause.

However, although an association with connective tissue disorders does exist, most people with spontaneous arterial dissections do not have associated connective tissue disorders. Also, the reports on the prevalence of hereditary connective tissue diseases in people with spontaneous dissections are highly variable, ranging from 0% to 0.6% in one study to 5% to 18% in another study.

Internal carotid artery dissection can also be associated with an elongated styloid process (known as Eagle syndrome when the elongated styloid process causes symptoms).

Traumatic
Carotid artery dissection is thought to be more commonly caused by severe violent trauma to the head and/or neck. An estimated 0.67% of patients admitted to the hospital after major motor vehicle accidents were found to have blunt carotid injury, including intimal dissections, pseudoaneurysms, thromboses, or fistulas. Of these, 76% had intimal dissections, pseudoaneurysms, or a combination of the two. Sports-related activities such as surfing and Jiu-Jitsu have been reported as causes of carotid artery dissection.

The probable mechanism of injury for most internal carotid injuries is rapid deceleration, with resultant hyperextension and rotation of the neck, which stretches the internal carotid artery over the upper cervical vertebrae, producing an intimal tear. After such an injury, the patient may remain asymptomatic, have a hemispheric transient ischemic event, or have a stroke.

Artery dissection has also been reported in association with some forms of neck manipulation. There is significant controversy about the level of risk of stroke from neck manipulation. It may be that manipulation can cause dissection, or it may be that the dissection is already present in some people who seek manipulative treatment.

Pathophysiology
Arterial dissection of the carotid arteries is a condition that arises when a small tear forms in the innermost lining of the arterial wall, known as the tunica intima. This tear allows blood to enter the space between the inner and outer layers of the vessel, leading to either narrowing (stenosis) or complete occlusion. Notably, the stenosis in the early stages of arterial dissection is a dynamic process, and some occlusions can quickly transition back to stenosis. When complete occlusion occurs, it can result in ischemia, a condition characterized by insufficient blood supply to a particular area.

It is interesting to note that even in cases of complete occlusion, symptoms may not always be evident due to the presence of collateral circulation, which helps to adequately perfuse the brain. However, complications can arise when blood clots develop at the site of the tear and subsequently break off, forming emboli. These emboli can then travel through the arteries and reach the brain, where they may block the blood supply. This blockage leads to an ischemic stroke, also known as a cerebral infarction. In fact, it is believed that blood clots or emboli originating from the dissection are responsible for causing infarctions in the majority of cases involving strokes in the presence of carotid artery dissection.

Cerebral infarction, as a result of carotid artery dissection, can cause irreversible damage to the brain. Studies have demonstrated a significant number of patients with dissections do go on to experience full blown strokes, often some time after the original dissection event. This emphasizes the serious and potentially life-altering consequences associated with this condition.

Treatment
The goal of treatment is to prevent the development of an actual stroke or limit the continuation of neurologic deficits should a stroke occur after dissection. Treatments include observation, anti-platelet agents, anticoagulation, stent implantation, carotid endarterectomy, and carotid artery ligation.

Epidemiology
Carotid dissections events can occur at any age. They tend to occur more often in younger individuals under 50. Such events are slightly more common in men than in women. Spontaneous internal carotid artery dissection is a rare event with an incidence rate of approximately 2.6 to 2.9 per 100,000 individuals. However, such events account for ~5% to ~22% of strokes in patients under the age of 45 years.