Pearls and Oy-sters: Carotid dissection with normal arterial lumen

DISCUSSION

Cervical artery dissection is a common cause of stroke in young and middle-aged adults.^1,2 The most frequent vessels involved are the ICA 2 cm above the bifurcation and vertebral artery at V3 segment.¹ Head trauma and high-speed neck manipulation are crucial predisposing factors of CAD.¹ Some conditions affecting the connective tissue (i.e., Ehlers-Danlos syndrome, Marfan syndrome, or osteogenesis imperfecta) have been reported to be associated with CAD.¹ The most common pathologic features include an intimal tear resulting in subintimal dissection. Less commonly, a medial or subadventitial dissection causing an intramural hematoma may occur.² Neurologic symptoms in arterial dissection can result from a cerebral infarction or TIA related to artery-to-artery embolism (due to platelet aggregation or localized luminal thrombus formation at the site of intimal injury) or secondary to a hemodynamic mechanism from a stenotic or occluded artery.³ CAD comprises a wide variety of clinical presentations, including 1) asymptomatic, 2) local signs and symptoms (e.g., headache, cervical pain, cranial nerve palsies, tinnitus, or Horner syndrome), or 3) TIA or focal neurologic deficits due to stroke.^1,2 Cranial nerve palsies, as a presenting sign in CAD, are rare. In a large study including 190 patients with spontaneous CAD, the authors reported that 12% presented with cranial nerve palsy, and 5.2% of them had a lower cranial palsy.⁴ The hypoglossal nerve (CN XII) is most commonly affected.^4,5 Less commonly, the V, VII, IX, X, and XI cranial nerves may also be involved. Ocular cranial nerve involvement has been described in intracranial CAD or progression of extracranial CAD (e.g., III, V, VI, affecting the cavernous segment of the ICA).^4,5 Cranial nerve palsies from CAD are usually explained by 2 mechanisms: 1) mechanical compression or stretching of the cranial nerves below the jugular foramen by the expanded artery or aneurysmal dilation at the origin of the dissection,⁶ or 2) impairment, transient or permanent, of the blood supply to the cranial nerves.^4,5 CN XII has only a somatic motor (general somatic efferent) component innervating all the intrinsic and 3 of the 4 extrinsic muscles of the tongue, including genioglossus, styloglossus, and hyoglossus. After passing through the hypoglossal canal, CN XII descends in the neck behind the vagus nerve and passes between ICA and internal jugular vein lying on the carotid sheath. Then, it courses over the internal and external carotid arteries and the hyoglossus muscle to supply tongue. CN XII compression or palsy results in tongue deviation to the ipsilateral side due to weakness of the innervated muscles and unopposed contraction of the contralateral genioglossus muscle. The close anatomic proximity to high cervical ICA explains its involvement in CAD.

The main diagnostic tools for CAD include MR angiogram, CT angiogram, and conventional angiogram. Classic findings include a luminal flap, false lumen, long tapered narrowing, or occlusion.^1,2 On cross-sectional imaging (especially MR), a characteristic sign of CAD is an enlarged artery with crescent-shaped rim of hyperintense signal surrounding a lumen, which may or may not be reduced in size. These signs can be demonstrated by T1-weighted axial cervical MRI with a fat saturation technique.^1,2 In our patient, the CT head also showed intramural hematoma within the upper cervical ICA at the skull base, suggesting dissection, and CT angiogram showed a cuff of abnormal soft tissue along the periphery of the vessel wall with preservation of luminal diameter. This case emphasizes the importance of looking at the vessel wall and not just the (filling) luminal contour, which can be normal.

The treatment of cervical artery dissection remains controversial. Anticoagulation or antiplatelet therapy is the mainstay. Currently, there is an ongoing randomized trial aimed at comparing the efficacy of antiplatelet vs anticoagulation in acute cervical dissections.⁷ In a meta-analysis including 34 nonrandomized studies (n = 762 patients), there was no difference in the risk of death (antiplatelet 5/268 [1.8%], anticoagulation 9/494 [1.8%], p = 0.88), stroke (antiplatelet 5/268 [1.9%], anticoagulant 10/494 [2.0%], p = 0.66), or stroke and death between antiplatelet and anticoagulation therapy.⁸ Overall, the prognosis in cervical artery dissection is good. Excellent outcome (defined as modified Rankin Scale score of 0–2) was reported in 92%.⁹ Recurrence rate is usually low (0.9%) after long-term follow-up.¹⁰