Spontaneous Dissections of Cervicocephalic Arteries

Etiology and Physiopathology

Dissection is a focal arteriopathy caused by a hematoma inside the arterial wall. It occurs most commonly in the extracranial and most mobile segments of the internal carotid and vertebral arteries. The specific vulnerability of this particular vascular segment to trauma is probably related to structural anatomical factors. The extracranial carotid segment is freely movable with a fixation at the entry into the carotid canal . Similarly, the extracranial vertebral artery also has high mobility when passing through the transverse foramina of the cervical spine . Not surprisingly, a history of cervical trauma in the prior month is strongly associated with a cervicocephalic artery dissection (CAD) . But the types of trauma leading to wall hematomas are diverse. A gross traumatic event involving the head and neck, such as motor vehicle accidents, assault strangulation or hanging attempt, is sometimes recalled. However, the trauma is reported to be “mild” in nearly 90% of cases . This includes trauma included in activities of daily living such as heavy lifting, spinal manipulative therapy , or practicing sports that involve rotation and accelerations. Nevertheless, the reporting of these relatively mild injuries in patients directly questioned about trauma raises natural concerns for recall biases so the concept of mechanical trigger event for CAD might be more appropriate . Occasionally, the early symptoms of medullary ischemia, such as paroxysmal sneezing, can be mistaken as a trigger . Also, the timing between the neck mechanical insult and neurological symptoms is quite variable, ranging from seconds to weeks, which further complicates the establishment of a causal relationship . When a mechanical trigger is minor or absent, the dissection can be considered spontaneous. While a predisposing arterial tendency to CAD is suspected in those cases, most patients do not have any identifiable disease or abnormal phenotype. A familial aggregation has been suggested, that would indicate a genetic predisposition . A minority of CAD are secondary to vulnerability due to identified connective tissue disorders, such as Ehlers–Danlos syndrome Type IV, Marfan syndrome, or osteogenesis imperfecta Type I .

Once an intimal tear occurs in the wall of the artery, the blood enters between the layers of the arterial wall splitting the media forming a false lumen. An intimal flap often separates the true lumen from the false lumen, which might be connected. If the hematoma is formed between the intima and the media layers, a long segment of arterial stenosis in the true lumen or total occlusion will occur. Conversely, if the hematoma occurs between the media and the adventitia, the artery may undergo a pseudoaneurysmal dilatation . Pathological changes in CAD occur at the media–adventitia border, and includes vacuolar degeneration, capillary neoangiogenesis, and erythrocyte extravasation . Facial or neck pain can result from the compression of arterial nerve endings by the intramural hematoma. The arterial expansion of the mural hematoma in CAD can also compress the sympathetic fibers wrapped around the carotid artery and cause Horner syndrome, or lower cranial neuropathies (cranial nerve (CN) IX to XII; less commonly CN V and VII) that may be mistaken for infiltrating skull base tumors. Often CAD results in cerebral ischemia. The infarcts from CAD that are commonly attributed to artery–artery embolization from a secondary luminal thrombus over the injured vessel, and less likely to a hemodynamic (flow-reduction) mechanism . Less commonly, the rupture of an intracranial pseudoaneurysm can result in a subarachnoid hemorrhage, typically with intracranial vertebral artery dissections ( Fig. 102.3 ).