Cerebrovascular Disease: Carotid Artery Dissection

Epidemiology

Spontaneous CAD is a rare condition with an approximate annual incidence of 2.6 per 100,000. However, since some cases may be clinically silent, the actual incidence may be higher. The mean age of patients with spontaneous dissection is 45 years. Although no clear evidence of gender or ethnic predisposition in the incidence of CAD exists, women tend to be younger and with multiple dissections at the time of diagnosis.

Pathophysiology

Spontaneous dissection of the carotid artery results from separation of the arterial wall layers causing blood to leak between these layers and forming a false lumen within the arterial wall. Evidence regarding the initial event causing the hemorrhage is still vague. It may be attributed to either a direct rupture of vasa vasorum or an intimal tear. Dissections can either be subadventitial or subintimal. Luminal stenosis is more common with subintimal dissection, while aneurysms often occur with subadventitial dissection. Examination of tissue samples from the dissected vessel reveals intramural hemorrhage. Granulation tissue replaces the intramural hematoma after 14 days of symptom onset with intimal enlargement along the false lumen. Neovascularization within the enlarged intimal layer starts after 30 days.

Etiology

Spontaneous CAD develops when there is an underlying impairment in vascular wall integrity that impairs arterial wall strength and makes it more vulnerable for dissection. In 40% of patients, there is a history of a provoking mechanical event preceding the symptoms. CAD has been found to be associated with multiple vascular and connective tissue diseases. Fibromuscular dysplasia accounts for approximately 15% of cases (see Ch. 143 , Fibromuscular Disease). Two percent of patients with Ehlers–Danlos syndrome type IV will develop CAD (see Ch. 141 , Arterial Disease in Patients with Connective Tissue Disorders). Other connective tissue diseases that may be associated with CAD include Marfan syndrome, osteogenesis imperfecta, homocystinuria, cystic medial necrosis, and alpha-1 antitrypsin deficiency. Nonetheless, it is unclear whether the incidence of CAD in these disorders is higher than the incidence by chance alone. CAD might also be associated with the presence of long styloid process; a rare condition called Eagle syndrome. The association between genetic factors and CAD has been suggested in light of the presence of familial cases without underlying connective tissue disease and the presence of accompanying arterial diseases, which suggests underlying arteriopathy. Another condition that might be associated with CAD includes aortic root dilatation. ^, Although chiropractic alteration of the neck has been reported in some cases of dissection, causality has not been supported. Recent infection was found to be associated with CAD; however, mechanical factors such as coughing, sneezing, and vomiting were not independently associated. ^, This may explain the seasonal variations of the disease during winter and autumn. Arterial hypertension and migraine were found to be independently associated with CAD. ^, However, no association has been observed between CAD and a history of smoking, diabetes, atherosclerosis, or prior oral contraceptive use.

Clinical Presentation

Headache and/or neck pain are the most common initial symptoms with spontaneous carotid dissection, with headache found in approximately 80% of cases. Headache is usually gradual in onset; however, severe sudden onset has been reported in 20% of cases. ^, Almost 25% develop Horner syndrome. Patients with internal carotid dissection may have partial Horner syndrome, which consists of ptosis and miosis only without anhidrosis. Transient ischemic attack and cerebral infarction occur in approximately 56% of cases. Ocular manifestations include painful transient loss of vision secondary to ischemic optic neuropathy, anisocoria, and amaurosis fugax. Patients with intracranial dissection can present with subarachnoid hemorrhage, which usually predicts a poor prognosis.

Cranial nerves are affected in about 12% of cases, particularly the lower cranial nerves (IX–XII). The hypoglossal nerve is most commonly affected, presenting with unilateral tongue paralysis in the form of tongue deviation towards the affected side due to unopposed action of the contralateral intact muscle. Other cranial nerve-related manifestations include loss of taste sensation with injury to the glossopharyngeal nerve, dysphagia and dysphonia with the vagus nerve, and shoulder drop with the spinal accessory nerve. Patients can also have bruit and tinnitus.

Etiology

Traumatic carotid artery dissection occurs after a blunt or sharp penetrating trauma. Intimal tear can occur secondary to rapid deceleration associated with motor vehicle accidents or any incident causing severe neck extension, lateral flexion, or rotation. Other mechanisms of blunt trauma include trauma to the oral cavity, and fractures of the mandible, cervical vertebrae, or skull base. Iatrogenic injury can also occur secondary to endovascular procedures.