The outer arterial wall layers are primarily affected in spontaneous cervical artery dissection

To evaluate the macroscopic and microscopic phenotype of the distal superficial temporal artery (STA) in patients with spontaneous cervical artery dissection (sCAD, n = 14). Arteries of accident victims, free of clinically apparent vascular disease, served as reference samples (n = 9).

Specimens of distal STA branches were obtained by biopsy or at autopsy. Their fine and ultrafine structure was documented by close-up photography of native STA branches, light microscopy, and electron microscopy in a case-control study.

STA specimens from patients with sCAD revealed pathologic changes mainly in the adventitial and medial layers. In these areas, vacuolar degeneration and fissuring were associated with neoangiogenesis of capillaries and microscopic erythrocyte extravasation into the connective tissue. In addition, some specimens showed overt microhematomas close to the medial/adventitial border visible at low magnification. The reference arteries showed virtually no pathologic changes in the outer arterial layers.

Bearing in mind that the STA is only a surrogate for the cervical arteries affected by sCAD, we propose the following pathogenetic model. We hypothesize that sCAD affects primarily the outer arterial layers. The process starts with degenerative changes at the medial-adventitial border associated with neoangiogenesis of capillary vessels branching from vasa vasorum in the adventitia. Leakage of neoangiogenetic capillaries releases blood cells into the connective tissue and leads to formation of microhematomas along the medial/adventitial border, as well as disintegration of the medial and adventitial texture. Microhematomas might then cause successive rupture of multiple neoangiogenetic capillaries and vasa vasorum, ultimately resulting in dissection.