Spontaneous Internal Carotid Artery Dissection

February 1, 2006
Christopher J. Pham, DO

,
Clark J. Okulski, DO

A 36-year-old man who had collapsedand sustained a bruised right shoulderwas brought to the emergency departmentwith acute emesis, cephalgia,blurred vision, aphasia, and righthemiparesis. He was confused but ableto follow simple commands.

A 36-year-old man who had collapsedand sustained a bruised right shoulderwas brought to the emergency departmentwith acute emesis, cephalgia,blurred vision, aphasia, and righthemiparesis. He was confused but ableto follow simple commands.

The patient was right-handed andworked as a computer programmer.He denied alcohol, tobacco, and illicitdrug use. The history included migraine,asthma, and a single incidentof spontaneous pneumothorax about10 years earlier. There was no personalhistory of stroke; however, family membershad been treated for hypertensionand stroke.

Blood pressure was normal.Pupils were equal (2.5 mm bilaterally)and reactive to light. The patient preferredthe left gaze visual field. Nopapilledema, exudates, or hemorrhagewas noted.

Right facial droop was apparent,but there was no tongue deviation.The patient complained of numbness inhis tongue, which he was unable toprotrude. No facial numbness or tinglingsensation was found.

A decreased carotid upstroke andbruit in the left carotid artery near theangle of the mandible were noted; agood pulsating left carotid pulse wasdetected 2 cm above the left clavicle.Right-sided strength was 0/5 in bothupper and lower extremities with spasticity;left-sided strength was 5/5throughout. Sensory response to pinprick,light touch, and temperaturewas significantly decreased on the rightside. Withdrawal from painful stimuliwas less pronounced on the rightside than the left. Bilateral Babinski,Oppenheimer, and Chaddock reflexeswere intact; clonus was absent.

An ECG showed sinus tachycardiawith normal sinus rhythm. Thecreatine kinase level was 102 U/L;creatine kinase MB isoenzyme,1.8 ng/mL; creatine kinase MB isoenzymeindex, 2; troponin T, lessthan 0.10 ng/mL; aspartate aminotransferase,22 U/L; alanine aminotransferase,16 U/L; and lactatedehydrogenase, 181 U/L. Cholesterollevel was 98 mg/dL; triglycerides,59 mg/dL; high-density lipoproteincholesterol, 34 mg/dL; low-densitylipoprotein 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; andcreatinine, 0.9 mg/dL. White bloodcell count was 11,300/μL; hemoglobin,12.2 g/dL; hematocrit, 35.7%;platelets, 190,000/μL; prothrombintime, 11.4 seconds; international normalizedratio (INR), 0.99; and partialthromboplastin time (PTT),26 seconds. Neither alcohol nor acetaminophenwas found in the serum.The urine drug screen was negativefor cocaine and other drugs.

Figure 1

The initial CT scan of the brainshowed a linear hyperdensity in theregion of the left middle cerebral artery,which indicated thrombus formation(Figure 1). An area of cerebral edemawas noted in the region with a smalleffacement from left to right. A cerebralangiogram performed 6 hours after theCT scan revealed a complete dissectionof the left internal carotid artery (ICA)from the second cervical segmentcraniad (Figure 2). A follow-up CTbrain scan 24 hours later demonstrateda large, left middle cerebral arteryischemic infarction with midline shiftingand evidence of left uncal herniation(Figure 3).


Anticoagulants were initiated.Although the patient was awake andaware of the environment, aphasia andright hemiparesis persisted. No evidenceof Horner syndrome (miosis, ptosis, andenophthalmos) was noted. A 2-dimensionalechocardiogram demonstrated nocardiac anomalies. Rehabilitation andspeech, physical, and occupational therapies were begun. The patient's vital signsremained unchanged.

After 1 month of rehabilitation,the patient's functional status returnedto baseline. He is now able to performactivities of daily living without significantdifficulty.

OVERVIEW
Internal carotid artery dissection(ICAD) can be traumatic orspontaneous.1 Spontaneous ICAD isthe cause of cerebral infarction in22% of otherwise healthy stroke patientsyounger than 30.1-4 One studyfound that about 40% of patients withspontaneous ICAD have a history ofmigraine.5

Carotid dissection is associatedwith cystic medial necrosis; syphiliticarteritis; α1-antitrypsin deficiency;and several heritable collagen disor-ders, including Marfan syndrome,Ehlers-Danlos syndrome, and type IIIcollagen deficiency.3,4,6,7 No gender differenceshave been reported.4,8 ICADand chronic and recurrent arterial dissectionare more likely to occur in patientswith fibromuscular dysplasia--particularly women.3,4

Hyperextension of the neck mayprecipitate a stretch injury to the ICA.However, a possible clinical correlationbetween carotid artery dissectionand cervical spine manipulation hasnot been proved.4


PATHOGENESIS
The pathogenesis of spontaneousICAD is unknown. Dissectinganeurysm causes an intramural hemorrhageinto the subintimal layer ofthe artery. The fragility and distensibilityof the arterial wall is related toan extracellular defect9; the mediaand subadventitial layers are involvedless frequently.4

A pseudoaneurysm forms whena dissection occurs between themedia and adventia layers. Generally,a pseudoaneurysm is caused bytrauma and is not demonstrated ona radiograph until several days afterthe injury. Typically found in thecervical portion of C1 and the skullbase, a pseudoaneurysm may becomeenlarged or remain stable, butit does not completely resolvespontaneously.

The cephalad extension ofICAD usually begins approximately2 cm distal to the carotid bulb andstops at the skull base region (apetrous portion), where the ICA beginsto enter the foramen lacerumto resume its normal caliber. Thedissection force courses in the longitudinalcephalad direction, sparingthe siphon.3,5

DIAGNOSISClinical features. ICAD can bean asymptomatic event or a severe,even catastrophic, ischemic episode.Persons with an arterial dissectionmay present initially with a transientischemic event. In the early stages ofICAD, the diagnosis is frequentlyoverlooked because the characteristicneurologic symptoms are not fullydeveloped. The pathognomonic clinicaltriad consists of facial or neckpain, ipsilateral Horner syndrome,and cerebral or retinal ischemicsymptoms.1,4

Horner syndrome, which is seenin 50% of patients with ICAD, is causedby injury to the pericarotid sympatheticplexus.10 Because of the plexus' adjacencyto the sympathetic chain, theaccessory, facial, glossopharyngeal,hypoglossal, or vagus nerves also maybe affected. Stretching of a dissectedvessel can impair the blood supply tothe cranial nerves and lead to cranialnerve palsies.11 Facial pain arises fromalteration of the trigeminal nerve fibers'distribution,9 and an ipsilateralpainful sensation is caused by pressurefrom the intramural hematomaon the nervi vasorum.

Cephalgia and Horner syndromeusually occur before ischemic symptoms.Cephalgia is more commonthan facial or neck pain.12 An ipsilateralcerebral or retinal ischemic event(such as amaurosis fugax, or transientmonocular or partial blindness)arises from subintimal thrombogenicembolism that results in cerebral hypoperfusion.4 Suspect ICAD when apatient who has not experienced traumacomplains of cephalgia with ipsilateralneck pain and tinnitus; thesesymptoms precede central retinalartery occlusion.13 Facial sweat functionis usually preserved because thesweat glands' sympathetic innervationpropagates along the externalcarotid artery.

Diagnostic studies. Ultrasonographyand magnetic resonanceangiography (MRA) are useful noninvasivemodalities for assessing thehemodynamic and morphologic featuresof ICAD. A "crescent" sign ona T1-weighted MRI scan representsa fresh intramural hematoma.14

Conventional intra-arterial angiography--long considered the "goldstandard" of diagnosis--may nolonger be necessary; the procedureposes the risk of cerebral complications.8 Angiography may reveal a slowlytapering occlusion or an irregularlongitudinal stenosis. A "string sign"--a segmental luminal constriction--isthe most distinctive angiographic finding.15 Another pathognomonic feature,the double-barrel lumen with muralflap, is found in only 4% of patients.

Carotid dissection related to fibromusculardysplasia is distinguished bya concentric narrowing of the lumenand may involve multiple arteries. Atheroscleroticarterial dissection usuallyoccurs at the bifurcation and at thecarotid siphon. Complete carotidstenosis of the distal branch of themiddle cerebral artery (MCA) producessevere neurologic deficits. A hyperdensemiddle cerebral artery(HMCA) demonstrated in a noncontrastCT scan represents a thromboembolismand is associated with alarge MCA ischemic infarction.6 A recentstudy showed that a hyperdensesylvian fissure MCA "dot sign" in patientswith acute ischemic stroke is amore reliable early marker of thromboembolicstroke of the distal MCAbranches than the HMCA sign.16

TREATMENT
The primary therapeutic goals areto prevent a complete stroke, to haltfurther progression of thromboembolism,and to resolve cerebral hypoperfusion.Anticoagulation therapy for6 months is the treatment of choice forICAD. Prompt administration of antico-agulants generally results in a good recoveryand functional outcome for thepatient. Improving cerebral blood flowduring the acute phase of stroke augmentscollateral circulation.

Medical therapy. Initially, beginintravenous heparin with a therapeuticgoal PTT of 50 to 60 seconds.17 Afterheparin is stopped, give oral warfarinto achieve a therapeutic INR of 2 to 3.Do not administer warfarin or antiplatelettherapy to a pregnant patient.

The use of recombinant tissueplasminogen activator (t-PA) iscontroversial. Some experts adviseagainst systemic thrombolysis becauseof an imminent risk of worseningintramural hemorrhage. In addition,the window for recombinantt-PA use is not clearly defined. However,the results of one study suggestthat intravenous t-PA (0.8mg/kg) is beneficial when givenwithin 7 hours of ischemic stroke relatedto ICAD.18

Antiplatelet therapy may be usedwhen anticoagulation is contraindicated.Because of the possible risk of endothelialproliferation, avoid estrogencontainingcompounds, especially forwomen with a history of fibromusculardysplasia.

We recommend routine follow-upMRAs at 1, 3, and 6 months after theinitial ICAD to assess the morphogenicproperty of the vessel lumen. Becausepatients with ICAD who are takinganticoagulants are at risk for bleeding,avoid invasive procedures, such ascerebral angiography.

Surgery. Consider surgical intervention--including carotid ligationwith or without superficial temporalartery-MCA anastomosis--when adequateanticoagulation therapy failsafter at least 6 months with evidenceof a persistent high-grade stenosis, orwhen a new aneurysm develops inthe dissected ICA.11

Endovascular stenting or coil embolizationare treatment options19-21;however, caution is necessary becauseendovascular maneuvers can cause distalthromboembolization.4

References:

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