This article series addresses high risk and low prevalence diseases that are encountered in the emergency department (ED). Much of the primary literature evaluating these conditions is not emergency medicine focused. By their very nature, many of these disease states and clinical presentations have little useful evidence available to guide the emergency physician in diagnosis and management. The format of each article defines the disease or clinical presentation to be reviewed, provides an overview of the extent of what we currently understand, and finally discusses pearls and pitfalls using a question and answer format. This article will discuss spontaneous cervical artery dissection (sCAD). This condition's low prevalence but high morbidity and mortality, as well as its variable atypical patient presentations and challenging diagnosis, make it a high risk and low prevalence disease. Of note, this review will not discuss in detail cervical artery dissection due to blunt or penetrating injury.

sCAD involves either the carotid artery or vertebral artery and occurs as a result of compromise of the arterial wall layers. This can lead to luminal stenosis, which may result in cerebral hypoperfusion and thromboembolic complications [[1], [2], [3], [4], [5], [6]]. This is a common cause of stroke in younger patients [[4], [5], [6], [7], [8], [9]]. While uncommon, sCAD is associated with significant morbidity and even mortality [4,6,9]. sCAD can be divided into the vessel affected (internal carotid versus vertebral) and location (extracranial versus intracranial) [4,6,9].

A dissection is a tear or separation of arterial wall layers, resulting in a false lumen where blood may enter the vessel wall between the intima and the media or between the media and the adventitia [1,[3], [4], [5], [6]]. Hemorrhage can occur due to intimal tear or be due to rupture of the vessel wall. Dissections affecting the subintimal area can result in luminal stenosis and complete occlusion, while subadventitial dissections can cause formation of a dissecting aneurysm [1,[3], [4], [5], [6]]. A false lumen may extend back into the true lumen, resulting in a double channel for blood flow [3,4]. Intramural hemorrhage, subintimal plane destruction, and separation of the media and adventitia may be present [1,[3], [4], [5], [6], [7]].

An intramural hematoma and subintimal dissection can cause luminal stenosis and occlusion, leading to cerebral ischemia from hypoperfusion, thromboembolism, or a combination of both. Current literature suggests that thromboembolism is the most likely underlying cause of cerebral ischemia, rather than hypoperfusion, in the setting of sCAD [6,[8], [9], [10], [11], [12], [13]]. Subadventitial dissections that result in formation of an aneurysm or hematoma, and vessel dilation can result in compression of local structures such as nerves and other vasculature [4,6].

The mechanism of sCAD is not completely understood and is likely multifactorial, occurring due to a combination of genetic, environmental, and acquired risk factors [4,6]. While most cases occur with a mechanical trigger, many patients will not recall an inciting event and are unaware of any major risk factors that lead to the vascular injury and dissection [14]. Risk factors include connective tissue disorders (e.g., fibromuscular dysplasia, Ehlers-Danlos syndrome) and vascular disease [13,15]. Ultimately, sCAD may lead to compressive symptoms due to involvement of structures around the dissection and ischemic symptoms due to vascular occlusion or emboli [3,4].

sCAD affecting the carotid may be intracranial or extracranial (Fig. 1). Intracranial carotid artery dissections most frequently occur in the supraclinoid segment, while extracranial carotid dissections occur 2 cm distal to the carotid bifurcation, around the skull base (Fig. 1) [4,16]. Vertebral dissection most commonly occurs in the transverse processes of C2-C6, affecting the V2 segment, or the C2 transverse process and foramen magnum at the skull base, affecting the V3 segment [[16], [17], [18]]. Importantly, multiple dissections are present in up to 22% of cases, more commonly in females, though <2% have three or more dissections simultaneously [6,[18], [19], [20], [21], [22], [23], [24], [25], [26]]. Dissections involving intracranial arteries are at a higher risk of rupture, as they have only a thin adventitial layer with no external elastic lamina as compared to the more robust extracranial arteries; this may lead to subarachnoid hemorrhage [6,[18], [19], [20], [21], [22], [23], [24], [25], [26]].

sCAD is not common, with one study suggesting an incidence of 1.72 per 100,000 individuals for internal carotid artery dissection, 0.97 per 100,000 individuals for vertebral artery dissection, and 2.6–3 per 100,000 for combined cases [4,6,[20], [21], [22], [23]]. However, this is likely an underestimation, as many patients are never diagnosed. Literature suggests that sCAD accounts for approximately 2% of strokes overall, but in patients <45 years, 15–24% of strokes are due to sCAD [[4], [5], [6], [7],27]. While this affects a younger population, with a mean age of 35 years to 53 years, there does not appear to be a predilection based on sex or ethnicity [8,12,19,20,22,24,28,29]. The literature is inconsistent regarding differences in incidence based on sex, with studies in North America suggesting women are more commonly affected, but in European studies men are more commonly affected [8,12,19,20,22,24,28,29]. Extracranial dissection is more common than intracranial dissection in North America and Europe, but intracranial dissection is more common in pediatric patients and Asian populations [4,8,20,23,24,29].