The location of origin of spontaneous extracranial internal carotid artery dissection is adjacent to the skull base

Introduction The traditional view is that spontaneous extracranial internal carotid artery (ICA) dissection (CAD) extends cranially from an intimal tear located just beyond the carotid bulb. This paper demonstrates that CAD originates in and primarily involves a more distal segment of the artery. Methods A retrospective study of 54 dissected ICAs in 50 consecutive patients with spontaneous or traumatic CAD was undertaken. The site of the dissection, presence of ICA redundancy, rate of acute or delayed ischaemic stroke and vessel remodelling were determined. Results Of the 51 dissections that occurred spontaneously or after indirect trauma, 25/51 (49.0%) were solely in the distal third of the artery, and 49/51 (96.1%) involved the distal two‐thirds. Only 2/51 (3.9%) originated in the proximal third. ICA redundancy was seen in 27/36 (75%) of patients with spontaneous CAD, compared with only 1/11 (9.1%) of those with CAD due to indirect trauma (P = 0.0002). Acute stroke occurred in 10/12 (83.3%) of patients with ICA occlusion secondary to CAD and in 14/38 (36.8%) with non‐occlusive CAD (P = 0.0074). Where follow‐up was available, only 2/32 (6.3%) patients had a stroke after diagnosis, and 19/33 (57.6%) ICAs recanalised or remodelled. Conclusion CAD occurring spontaneously or due to indirect trauma most frequently involves the distal extracranial ICA. Spontaneous CAD is associated with vessel redundancy, and the risk of acute stroke is greatest with occlusive CAD. The prognosis is good with treatment, with a low rate of recurrent stroke and a high rate of vessel remodelling.