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Fig. 9. CTA of the neck showing the presence of a luminal narrowing starting 2 cm above the RCA bifurcation and extending to the base of the skull (string sign).

Angiography can also document underlying abnormalities that can predispose to arterial dissections such as fibromuscular dysplasia and internal carotid artery redundancies (loops, coils and kinks).

Even though angiography is still considered the gold standard for diagnosis of carotid dissection, it carries an increased risk of complications [46] since it is an invasive technique. Also, a double lumen and intimal flaps are rarely visualized with this technique [6], [67], [16] and the external wall is also rarely visualized.

Differential diagnosis

Cluster headaches might be confounded with an ICA dissection since classically it presents as facial pain and an ipsilateral Horner's syndrome, however the episodes are usually brief and focal signs rarely occur [77].

Complicated migraine is also in the differential, even though most of the time, the patients recognize the attacks as their usual migraine. Changes in the characteristics of the headache should raise a red flag, since a possible association between mi

Intimal Flap Carotid Artery
Fig. 10. CTA showing an increase in the diameter of the LICA (arrow) and the presence of an intimal flap (bent-up arrow).

graines and arterial dissections has been described [90], [37].

Herpes zoster involving the ophthalmic branch of the trigeminal nerve can also mimic dissection initially since it presents with unilateral facial pain and blurred vision before the typical rash develops [93].

Treatment

There have been no controlled trials of medical therapy for the treatment of ICA dissections. Some authors, with the goal of preventing intra-arterial embolism and further strokes, have advocated short-term anticoagulation with heparin followed by Cou-madin [19], [79], [12], [58]. The long-term safety of antithrombotic therapy (anticoagulants or antiplatelets) has been shown in patients with carotid artery dissection [34] and the potential risk of a spread of mural hematoma, which has prevented some authors from using heparin, has never been demonstrated [40], [96]. The optimal duration of anticoagulation has not been established, but treatment for 3 to 6 months is usually advocated. Anticoagulation may be stopped earlier if complete recanalization is demonstrated or may be continued in cases of persistent stenosis of the artery. In patients with chronic occlusion of the artery, there is probably no benefit of continuing anticoagulation [19], [96].

The feasibility of IV TPA in patients with acute ischemic stroke secondary to carotid dissection has also been demonstrated [30], [5].

Fortunately in the vast majority of the cases there is complete recanalization and healing of the dissected arteries within the first few months of the initial event [90], [16], [87], [6], [67], [15]. However, in a subgroup of patients, the recanalization of the vessel fails to occur and patients are left with severely stenotic vessels, sometimes associated with

String Sign Carotid
Fig. 11. Cerebral angiography showing a stenotic type of ICA dissection ("string sign").

pseudoaneurysm formation. In such cases anticoagulation will prevent further thromboembolic events, but not hemodynamic ones associated with low cerebral blood flow. Also, at times, anticoagu lation may be contraindicated because of the risk of pseudoaneurysm rupture [3]. Occasionally, the false lumen can remain patent.

Surgeries including carotid ligation, resection with revascularization and bypass have been used when symptoms progress despite the best medical treatment or when a pseudoaneurysm is present. More recently, stents with and without coil placement have provided a new option for some of those patients with successful results [14], [23], [24], [59].

Prognosis

The prognosis of extracranial dissections is quite heterogeneous varying from asymptomatic cases (approximately 5% of the patients) to major sequelae and death in about 15% of the patients. However, most of the patients have excellent or good recovery [89], [87], [56].

Complete recanalization of the ICA occurs in approximately two thirds of patients with occluded vessels and 90% of patients with initial stenosis, usually within the first two months of symptom onset [90]. Rarely, recanalization is detected after 6 months of a dissection.

Recurrence rates for arterial dissection vary in different series from 3-8% [56], [11], [80] and are higher in younger patients, patients with positive family history or patients with an underlying arterio-pathy [56], [11], [80], [81], [38].

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