# Cervicocephalic Arterial Dissection

## Overview

Cervicocephalic arterial dissection (CAD) involves tearing of the intimal layer of the carotid or vertebral artery, allowing blood to track into the vessel wall. It is an important cause of stroke in young and middle-aged adults, accounting for approximately 25% of strokes in patients under 45 years of age. The clinical presentation may include headache, neck pain, Horner syndrome, cranial neuropathies, or ischemic stroke and TIA. Treatment with antithrombotics remains the mainstay, and the overall prognosis is generally favorable.

## Anatomy and Pathophysiology

An intimal tear allows blood to dissect into the media, creating an intramural hematoma. This hematoma can produce several consequences. It may cause luminal stenosis or complete occlusion, reducing blood flow and creating the potential for hemodynamic stroke. It may create an intimal flap that serves as a nidus for thrombus formation, leading to artery-to-artery embolism, which is the most common stroke mechanism in dissection. It may produce a pseudoaneurysm through aneurysmal dilation of the vessel wall. It may also compress adjacent structures, including the sympathetic chain (producing Horner syndrome) and cranial nerves XII, IX, and X.

### Carotid Artery Dissection

Carotid dissection most commonly affects the extracranial internal carotid artery, typically 2-3 cm distal to the bifurcation in the pharyngeal segment. This portion of the ICA is mobile and susceptible to mechanical injury. Intracranial ICA dissection is less common but more dangerous because of the risk of subarachnoid hemorrhage.

### Vertebral Artery Dissection

Vertebral dissection most commonly occurs at the V3 segment (the atlas loop), where the artery is mobile and vulnerable to rotational and flexion forces. Intracranial vertebral dissection can extend to the basilar artery and may cause SAH.

## Etiology and Risk Factors

### Traumatic / Mechanical

Mechanical causes include motor vehicle accidents (especially with seatbelt injury), chiropractic manipulation (particularly cervical manipulation, which is associated with vertebral artery dissection), and sports injuries from martial arts, contact sports, or roller coasters. Even minor trauma such as vigorous coughing, sneezing, vomiting, yoga, or painting a ceiling can trigger dissection. Many cases involve trivial or no identifiable preceding trauma.

### Connective Tissue Disorders

Fibromuscular dysplasia (FMD) is found in 15-20% of CAD patients, producing the characteristic "string of beads" appearance on angiography. Other associated connective tissue disorders include Ehlers-Danlos syndrome (type IV, vascular), Marfan syndrome, osteogenesis imperfecta, and alpha-1 antitrypsin deficiency.

### Other Risk Factors

Additional risk factors include recent upper respiratory infection (which may cause inflammatory vessel wall weakening), hypertension (a modest association), migraine (an epidemiologic association possibly reflecting shared vascular pathology), and oral contraceptive use (a weak association).

## Clinical Presentation

| Feature | Carotid Artery Dissection | Vertebral Artery Dissection |
|---|---|---|
| Most common site | Extracranial ICA, 2–3 cm distal to bifurcation | V3 segment (atlas loop) |
| Pain location | Ipsilateral head, face, or neck | Posterior neck or occipital headache |
| Characteristic sign | Partial Horner syndrome (miosis + ptosis, no anhidrosis) | Lateral medullary (Wallenberg) syndrome |
| Cranial neuropathy | CN XII (tongue deviation toward lesion) | Rare |
| Stroke territory | MCA | Posterior circulation |
| SAH risk | Rare (intracranial extension required) | If intracranial V4 extension |

### Carotid Artery Dissection

Pain is the most common symptom, occurring in 60-90% of patients as ipsilateral head, face, or neck pain, often described as sharp or throbbing. Pain may precede neurological symptoms by hours to days. A partial Horner syndrome produces miosis and ptosis without anhidrosis; the sympathetic fibers traveling along the ICA are affected distal to the point where sudomotor fibers branch off, explaining the preservation of facial sweating. Ischemic stroke or TIA occurs most commonly in the MCA territory and may present at the time of dissection or days later. Cranial neuropathies occur, with CN XII (tongue deviation toward the dissection side) being most common due to the proximity of the hypoglossal nerve to the ICA in the parapharyngeal space; CN IX and X can also be affected. Pulsatile tinnitus results from turbulent flow through the narrowed ICA. The classic triad of pain, Horner syndrome, and delayed cerebral ischemia is present in only about one-third of patients.

### Vertebral Artery Dissection

Posterior neck pain or occipital headache is typically sharp and unilateral. Posterior circulation stroke may manifest as lateral medullary (Wallenberg) syndrome, which is the classic presentation, or may present with vertigo, ataxia, diplopia, or dysphagia. SAH can occur if there is intracranial extension to the V4 segment with rupture. Cervical radiculopathy from compression by the dissecting hematoma is rare.

## Diagnosis

### CT Angiography (CTA)

CTA is the first-line imaging modality in the acute stroke setting. Findings include luminal narrowing or occlusion, intimal flap, mural thickening (the crescent sign on axial images), and pseudoaneurysm. Sensitivity for extracranial dissection exceeds 95%.

### MRI/MRA with Fat-Saturated T1 Sequences

Axial fat-saturated T1 MRI is the gold standard for visualizing intramural hematoma, which appears as a hyperintense crescent surrounding the narrowed flow void. MRA demonstrates stenosis, occlusion, or pseudoaneurysm. The intramural hematoma may not be visible in the first 24-48 hours because it is isointense on T1 in the hyperacute phase; it is best seen after 48-72 hours once methemoglobin appears. Combined sensitivity and specificity exceed 95% for extracranial dissection.

### Vessel Wall MRI

High-resolution vessel wall imaging can directly visualize intramural hematoma and distinguish dissection from atherosclerosis or vasculitis. It is increasingly used in academic centers.

### Digital Subtraction Angiography (DSA)

DSA remains the gold standard but is invasive and reserved for equivocal cases. Findings include the "string sign" (a long segment of narrowing), "flame-shaped" occlusion, pseudoaneurysm, and intimal flap.

### Ultrasound (Duplex)

Duplex ultrasound may show a high-resistance flow pattern, tapering stenosis, or intramural hematoma in carotid dissection. It is operator-dependent and limited for the vertebral artery and intracranial segments, but useful for serial monitoring of recanalization.

## Treatment

### Antithrombotic Therapy

Because the primary mechanism of stroke in dissection is artery-to-artery thromboembolism, antithrombotic therapy is the cornerstone of treatment.

The CADISS trial (2015) randomized patients to antiplatelet versus anticoagulation within 7 days of symptomatic CAD and found no significant difference in recurrent stroke rate between groups. The recurrence rate was very low overall, approximately 2% at 3 months in both arms, and the study was underpowered to detect a small difference.

In current practice, antiplatelet therapy with aspirin or clopidogrel is preferred by many clinicians due to equivalent efficacy and a lower bleeding risk. Anticoagulation with heparin bridged to warfarin or a DOAC is preferred by some for patients with high-grade stenosis, free-floating thrombus, or recurrent events on antiplatelets. For intracranial dissection with SAH, anticoagulation must be avoided due to the risk of worsening hemorrhage, and endovascular treatment may be required. The typical duration of antithrombotic therapy is 3-6 months, with reassessment guided by follow-up imaging.

### Endovascular and Surgical Interventions

Stenting is reserved for cases with recurrent ischemic events despite antithrombotic therapy or hemodynamically significant stenosis. Coiling or flow diversion is used for dissecting pseudoaneurysms causing mass effect or at risk of rupture. Surgical repair is rarely needed and is considered mainly for traumatic dissection with ongoing hemorrhage.

### Follow-Up Imaging

Repeat CTA or MRA at 3-6 months assesses recanalization, which occurs in 60-80% of cases. Pseudoaneurysms typically remain stable and rarely enlarge or rupture. The decision to continue or stop antithrombotics is guided by imaging findings: persistent stenosis or thrombus favors continuation, while complete recanalization supports discontinuation.

## Prognosis

The overall prognosis is favorable, with more than 75% of patients achieving a good functional outcome. The risk of recurrent dissection is approximately 1-2% per year. The risk of stroke after dissection is highest in the first two weeks and decreases significantly after one month. Pseudoaneurysms persist in 30-50% of cases but rarely cause symptoms.

<image>An anatomical illustration showing carotid and vertebral artery dissection. The left panel shows the extracranial ICA with an intimal tear and intramural hematoma causing luminal stenosis, with adjacent sympathetic fibers (explaining Horner syndrome) and CN XII (explaining tongue deviation). The right panel shows the vertebral artery at the V3 segment (atlas loop) with dissection. Inset cross-sectional diagrams show the normal artery wall layers compared to a dissected artery with intramural hematoma creating a crescent-shaped narrowing of the lumen. The mechanism of stroke (artery-to-artery thromboembolism from the intimal flap) is illustrated with a small embolus traveling distally.</image>

<image>A diagnostic imaging comparison panel for cervical artery dissection. Panel A: axial fat-saturated T1 MRI showing a hyperintense intramural hematoma (crescent sign) surrounding the narrowed ICA flow void. Panel B: MRA showing long-segment narrowing ("string sign") of the extracranial ICA. Panel C: CTA showing a pseudoaneurysm of the vertebral artery. Panel D: DSA showing flame-shaped ICA occlusion. Each panel is labeled with the key diagnostic finding and the imaging modality's strengths and limitations.</image>

## Clinical Pearls

Dissection should be suspected in any young or middle-aged patient presenting with unilateral head or neck pain followed by ischemic stroke or TIA, particularly in the absence of traditional vascular risk factors. A partial Horner syndrome (miosis and ptosis without anhidrosis) with ipsilateral headache is highly suggestive of ICA dissection. Fat-saturated T1 MRI is the best sequence for visualizing intramural hematoma, but it may be negative in the first 24-48 hours. The CADISS trial showed no difference between antiplatelet and anticoagulation therapy, and antiplatelet treatment is increasingly preferred for its simplicity and safety profile. Vertebral artery dissection classically presents with posterior neck or occipital pain followed by posterior circulation stroke, particularly Wallenberg syndrome. Screening for fibromuscular dysplasia should be performed in dissection patients, as it is found in 15-20% and may influence management. Chiropractic cervical manipulation is a recognized risk factor for vertebral artery dissection.

## References
- Markus HS, et al. Antiplatelet treatment compared with anticoagulation treatment for cervical artery dissection (CADISS). Lancet Neurol. 2015;14(4):361-367.
- Debette S, et al. Cervical artery dissection: diagnosis, management, and treatment. Lancet Neurol. 2015;14(6):640-654.
- Schievink WI. Spontaneous dissection of the carotid and vertebral arteries. N Engl J Med. 2001;344(12):898-906.
- Robertson JJ, Koyfman A. Cervical artery dissections: a review of the literature. J Emerg Med. 2016;51(5):508-518.