Carotid artery dissection

Carotid artery dissection is a tear in the intima of the carotid artery wall causing separation of the wall layers. The carotid artery supplies blood to the head and brain. Carotid dissection is an important cause of stroke in young adults.

Arterial dissection of the carotid arteries occurs when a small tear in the innermost lining of the arterial wall forms. Blood can enter into the space between the inner and outer layers of the vessel, creating an intraluminal hematoma which forms a thrombus causing narrowing (stenosis) or complete occlusion. This thrombus can act as a nidus for distal embolization to the brain. Extracranial dissection of internal carotid artery is more frequent than intracranial dissection. The stenosis that occurs in the early stages of arterial dissection is a dynamic process and some occlusions can return to stenosis very quickly^[1]. When complete occlusion occurs, it may lead to ischemia. Often, even a complete occlusion is totally asymptomatic because collateral circulation in the head keeps the brain well perfused. However, when blood clots form and break off from the site of the tear, the clots travel through the blood to the brain and clog one or more of the arteries directly supplying the brain, resulting in an ischemic stroke, otherwise known as an infarct. Blood clots, or emboli, originating from the dissection are thought to be the cause of infarction in the majority of cases of stroke in the presence of carotid artery dissection. Cerebral infarction causes irreversible damage to the brain. In one study of patients with carotid artery dissection, 60% had infarcts documented on neuroimaging^[2][1] .

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

Once considered uncommon, spontaneous carotid artery dissection is an increasingly recognized cause of stroke that preferentially affects the middle-aged^[3].

Observational studies and case reports published since the early 1980s show that patients with spontaneous internal carotid artery dissection may also have hereditary connective tissue disorders. These include:

• Marfan syndrome
• Vascular Ehlers-Danlos syndrome
• Autosomal Dominant Polycystic Kidney Disease
• Pseudoxanthoma elasticum
• Fibromuscular dysplasia
• Osteogenesis imperfecta type I
• Hypertension
• Cystic medial necrosis

Nevertheless, although an association exists with connective tissue disorders does exist, most people with spontaneous arterial dissections do not have associated connective tissue disorders.

Carotid artery dissection is more commonly thought to be caused by trauma to the head and/or neck. 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^[4]. After such an injury, the patient may remain asymptomatic, have a hemispheric transient ischemic event, or suffer a stroke^[5].

Carotid artery dissection should be differentiated form the following:

• Vertebral artery dissection
• Neck trauma
• Headache
• Subarachnoid hemorrhage

• The annual incidence of spontaneous carotid artery dissection is low, and incidence rates for internal carotid artery dissection have been reported to be 2.6 to 2.9 per 100,000^[6].
• Prevalence of hereditary connective tissue diseases in people with spontaneous dissections is highly variable, ranging from 0% to 0.6% in one study to 5% to 18% in another study.
• An estimated 0.67% of patients admitted to the hospital after motor vehicle accidents were found to have blunt carotid injury, including intimal dissections, pseudoaneurysms, thromboses, or fistulas^[7]. Of these, 76% had intimal dissections, pseudoaneurysms, or a combination of the two.
• Gender is not associated with an increased risk of carotid artery dissection.

• Ischemic stroke
• Retinal ischemic injury – transient loss of vision

Prognosis of carotid artery dissection is favorable with 75% of patients having a good recovery. Traumatic dissection is associated with a higher mortality rate on discharge compared to spontaneous dissection. Two important prognostic factors include:

• Initial ischemic injury
• Collateral circulation

Common symptoms of carotid artery dissection include:

• Headache
• Tinnitus
• Neck pain
• Horner syndrome
• Transient loss of vision

• Ptosis
• Miosis

• Complete blood count
• Coagulation studies
  • Prothrombin time (PT)
  • Activated partial thromboplastin time (aPTT)

Helical CT angiography is a reliable method to diagnose carotid artery dissections. Findings on a helical CT angiography include:

• Narrowed eccentric lumen
• Arterial wall thickening
• Thin annular contrast enhancement
• Enlargement of the dissected artery

Also, the finding of a fractured cervical bone should raise the suspicion for carotid artery dissection.

Advantages include:

• Fast
• Noninvasive

MRA has evolved as an excellent imaging modality to screen and diagnose carotid artery dissection and is superior to the conventional angiography. The classic findings on an MRA include:

• Intraluminal hematoma which appears hyperintense on fat-suppressed, axial T1 and T2 weighted images
• Mural expansion

Other findings include:

• Irregular vessel margins
• Filling defects
• Vascular occlusion
• Caliber changes of the vessel

Advantages of MRA:

• High resolution
• No radiation
• Good negative predictive value

Disadvantages include:

• Failure to detect the intramural hematoma with in the first 24-48 hours after carotid artery dissection

Doppler ultrasonography (DUS) is used as an initial assessment of carotid artery dissection. Findings inlude:

• Appearance of a membrane, which is appreciated in both longitudinal and axial views
• Visualization of a false lumen even when it is thrombosed

The goal of treatment is to prevent the development or continuation of neurologic deficits. Treatments include

• Observation
• Aanticoagulation
• Stent implantation
• Carotid artery ligation

• Aortic dissection

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