Spontaneous Internal Carotid Artery Dissection

A 36-year-old man who had collapsed and sustained a bruised right shoulder was brought to the emergency department with acute emesis, cephalgia, blurred vision, aphasia, and right hemiparesis. He was confused but able to follow simple commands.

The patient was right-handed and worked as a computer programmer. He denied alcohol(, tobacco, and illicit drug use. The history included migraine, asthma, and a single incident of spontaneous pneumothorax about 10 years earlier. There was no personal history of stroke; however, family members had been treated for hypertension and stroke.

Blood pressure was normal. Pupils were equal (2.5 mm bilaterally) and reactive to light. The patient preferred the left gaze visual field. No papilledema, exudates, or hemorrhage was noted.

Right facial droop was apparent, but there was no tongue deviation. The patient complained of numbness in his tongue, which he was unable to protrude. No facial numbness or tingling sensation was found.

A decreased carotid upstroke and bruit in the left carotid artery near the angle of the mandible were noted; a good pulsating left carotid pulse was detected 2 cm above the left clavicle. Right-sided strength was 0/5 in both upper and lower extremities with spasticity; left-sided strength was 5/5 throughout. Sensory response to pinprick, light touch, and temperature was significantly decreased on the right side. Withdrawal from painful stimuli was less pronounced on the right side than the left. Bilateral Babinski, Oppenheimer, and Chaddock reflexes were intact; clonus was absent.

An ECG showed sinus tachycardia with normal sinus rhythm. The creatine kinase level was 102 U/L; creatine kinase MB isoenzyme, 1.8 ng/mL; creatine kinase MB isoenzyme index, 2; troponin T, less than 0.10 ng/mL; aspartate aminotransferase, 22 U/L; alanine aminotransferase, 16 U/L; and lactate dehydrogenase, 181 U/L. Cholesterol level was 98 mg/dL; triglycerides, 59 mg/dL; high-density lipoprotein cholesterol, 34 mg/dL; low-density lipoprotein cholesterol, 52 mg/dL; very-low-density lipoprotein cholesterol, 12 mg/dL; total bilirubin, 0.5 mg/dL; thyrotropin, 1.15 μIU/mL; blood urea( nitrogen, 12 mg/dL; and creatinine, 0.9 mg/dL. White blood cell count was 11,300/μL; hemoglobin, 12.2 g/dL; hematocrit, 35.7%; platelets, 190,000/μL; prothrombin time, 11.4 seconds; international normalized ratio (INR), 0.99; and partial thromboplastin time (PTT), 26 seconds. Neither alcohol nor acetaminophen was found in the serum. The urine drug screen was negative for cocaine and other drugs.

Figure 1

The initial CT scan of the brain showed a linear hyperdensity in the region of the left middle cerebral artery, which indicated thrombus formation (Figure 1). An area of cerebral edema was noted in the region with a small effacement from left to right. A cerebral angiogram performed 6 hours after the CT scan revealed a complete dissection of the left internal carotid artery (ICA) from the second cervical segment craniad (Figure 2). A follow-up CT brain scan 24 hours later demonstrated a large, left middle cerebral artery ischemic infarction with midline shifting and evidence of left uncal herniation (Figure 3).

Figure 2	Figure A
	Figure B

Anticoagulants were initiated. Although the patient was awake and aware of the environment, aphasia and right hemiparesis persisted. No evidence of Horner syndrome (miosis, ptosis, and enophthalmos) was noted. A 2-dimensional echocardiogram demonstrated no cardiac anomalies. Rehabilitation and speech, physical, and occupational therapies were begun. The patient's vital signs remained unchanged.

After 1 month of rehabilitation, the patient's functional status returned to baseline. He is now able to perform activities of daily living without significant difficulty.

OVERVIEW
Internal carotid artery dissection (ICAD) can be traumatic or spontaneous.¹ Spontaneous ICAD is the cause of cerebral infarction in 22% of otherwise healthy stroke patients younger than 30.^1-4 One study found that about 40% of patients with spontaneous ICAD have a history of migraine.⁵

Carotid dissection is associated with cystic medial necrosis; syphilitic arteritis; α₁-antitrypsin deficiency; and several heritable collagen( disor- ders, including Marfan syndrome, Ehlers-Danlos syndrome, and type III collagen deficiency.^3,4,6,7 No gender differences have been reported.^4,8 ICAD and chronic and recurrent arterial dissection are more likely to occur in patients with fibromuscular dysplasia— particularly women.^3,4

Hyperextension of the neck may precipitate a stretch injury to the ICA. However, a possible clinical correlation between carotid artery dissection and cervical spine manipulation has not been proved.⁴

Figure 3

Figure 3b

PATHOGENESIS
The pathogenesis of spontaneous ICAD is unknown. Dissecting aneurysm causes an intramural hemorrhage into the subintimal layer of the artery. The fragility and distensibility of the arterial wall is related to an extracellular defect⁹; the media and subadventitial layers are involved less frequently.⁴

A pseudoaneurysm forms when a dissection occurs between the media and adventia layers. Generally, a pseudoaneurysm is caused by trauma and is not demonstrated on a radiograph until several days after the injury. Typically found in the cervical portion of C1 and the skull base, a pseudoaneurysm may become enlarged or remain stable, but it does not completely resolve spontaneously.

The cephalad extension of ICAD usually begins approximately 2 cm distal to the carotid bulb and stops at the skull base region (a petrous portion), where the ICA begins to enter the foramen lacerum to resume its normal caliber. The dissection force courses in the longitudinal cephalad direction, sparing the siphon.^3,5

DIAGNOSIS
Clinical features. ICAD can be an asymptomatic event or a severe, even catastrophic, ischemic episode. Persons with an arterial dissection may present initially with a transient ischemic event. In the early stages of ICAD, the diagnosis is frequently overlooked because the characteristic neurologic symptoms are not fully developed. The pathognomonic clinical triad consists of facial or neck pain, ipsilateral Horner syndrome, and cerebral or retinal ischemic symptoms.^1,4

Horner syndrome, which is seen in 50% of patients with ICAD, is caused by injury to the pericarotid sympathetic plexus.¹⁰ Because of the plexus’ adjacency to the sympathetic chain, the accessory, facial, glossopharyngeal, hypoglossal, or vagus nerves also may be affected. Stretching of a dissected vessel can impair the blood supply to the cranial nerves and lead to cranial nerve palsies.¹¹ Facial pain arises from alteration of the trigeminal nerve fibers’ distribution,⁹ and an ipsilateral painful sensation is caused by pressure from the intramural hematoma on the nervi vasorum.

Cephalgia and Horner syndrome usually occur before ischemic symptoms. Cephalgia is more common than facial or neck pain.¹² An ipsilateral cerebral or retinal ischemic event (such as amaurosis fugax, or transient monocular or partial blindness) arises from subintimal thrombogenic embolism that results in cerebral hypoperfusion. ⁴ Suspect ICAD when a patient who has not experienced trauma complains of cephalgia with ipsilateral neck pain and tinnitus; these symptoms precede central retinal artery occlusion.¹³ Facial sweat function is usually preserved because the sweat glands’ sympathetic innervation propagates along the external carotid artery.

Diagnostic studies. Ultrasonography and magnetic resonance angiography (MRA) are useful noninvasive modalities for assessing the hemodynamic and morphologic features of ICAD. A “crescent” sign on a T1-weighted MRI scan represents a fresh intramural hematoma.¹⁴

Conventional intra-arterial angiography— long considered the “gold standard” of diagnosis—may no longer be necessary; the procedure poses the risk of cerebral complications. ⁸ Angiography may reveal a slowly tapering occlusion or an irregular longitudinal stenosis. A “string sign”— a segmental luminal constriction—is the most distinctive angiographic finding. ¹⁵ Another pathognomonic feature, the double-barrel lumen with mural flap, is found in only 4% of patients.

Carotid dissection related to fibromuscular dysplasia is distinguished by a concentric narrowing of the lumen and may involve multiple arteries. Atherosclerotic arterial dissection usually occurs at the bifurcation and at the carotid siphon. Complete carotid stenosis of the distal branch of the middle cerebral artery (MCA) produces severe neurologic deficits. A hyperdense middle cerebral artery (HMCA) demonstrated in a noncontrast CT scan represents a thromboembolism and is associated with a large MCA ischemic infarction.⁶ A recent study showed that a hyperdense sylvian fissure MCA “dot sign” in patients with acute ischemic stroke is a more reliable early marker of thromboembolic stroke of the distal MCA branches than the HMCA sign.¹⁶

TREATMENT
The primary therapeutic goals are to prevent a complete stroke, to halt further progression of thromboembolism, and to resolve cerebral hypoperfusion. Anticoagulation therapy for 6 months is the treatment of choice for ICAD. Prompt administration of antico- agulants generally results in a good recovery and functional outcome for the patient. Improving cerebral blood flow during the acute phase of stroke augments collateral circulation.

Medical therapy. Initially, begin intravenous heparin with a therapeutic goal PTT of 50 to 60 seconds.¹⁷ After heparin is stopped, give oral warfarin( to achieve a therapeutic INR of 2 to 3. Do not administer warfarin or antiplatelet therapy to a pregnant patient.

The use of recombinant tissue plasminogen activator (t-PA) is controversial. Some experts advise against systemic thrombolysis because of an imminent risk of worsening intramural hemorrhage. In addition, the window for recombinant t-PA use is not clearly defined. However, the results of one study suggest that intravenous t-PA (0.8 mg/kg) is beneficial when given within 7 hours of ischemic stroke related to ICAD.¹⁸

Antiplatelet therapy may be used when anticoagulation is contraindicated. Because of the possible risk of endothelial proliferation, avoid estrogencontaining compounds, especially for women with a history of fibromuscular dysplasia.

We recommend routine follow-up MRAs at 1, 3, and 6 months after the initial ICAD to assess the morphogenic property of the vessel lumen. Because patients with ICAD who are taking anticoagulants are at risk for bleeding, avoid invasive procedures, such as cerebral angiography.

Surgery. Consider surgical intervention— including carotid ligation with or without superficial temporal artery–MCA anastomosis—when adequate anticoagulation therapy fails after at least 6 months with evidence of a persistent high-grade stenosis, or when a new aneurysm develops in the dissected ICA.¹¹

Endovascular stenting or coil embolization are treatment options^19-21; however, caution is necessary because endovascular maneuvers can cause distal thromboembolization.⁴