Commonest location of arterial lesions

The most common vascular lesion that causes posterior circulation infarction is located within the proximal portions of the extracranial vertebral arteries (ECVAs) (Caplan 1996). Atherosclerosis most often affects the first few centimetres of the ECVAs after their origin from the subclavian arteries (Hutchinson & Yates, 1956; Caplan, 1996). Sometimes plaques extend from the subclavian arteries into the proximal ECVAs. Occlusive lesions at this site are most common in white men (Gorelick et al., 1985; Caplan, 1996). Hypertension, hypercholesterolemia, coronary artery disease, peripheral vascular occlusive disease, and atherostenotic lesions in the proximal internal carotid arteries often accompany the ECVA lesions (Gorelick et al., 1985; Caplan, 1996; Yates & Hutchinson, 1957). Black people, Asians and women less often have occlusive ECVA disease. ECVA lesions cause transient hypoperfusion. The major mechanism of posterior circulation infarction, in patients with ECVA atherosclerosis, is intra-arterial embolism (Caplan, 1991, 1996; Caplan et al., 1992; Caplan & Tettenborn 1992a; Wityk et al., 1998).

Atherosclerosis is unusual in the portion of the ECVA that traverses the transverse foramena or in the distal portions of the ECVA before dural penetration. The predominant lesion within the second and third portions of the ECVA is dissection (Caplan et al., 1985; Caplan & Tettenborn, 1992b; Chiras et al., 1985; Mas et al., 1987; Mokri et al., 1988). Dissections that involve the distal ECVA sometimes extend into the intracranial vertebral artery (ICVA). Thrombus within the lumen of the dissected artery may propagate into the ICVA or embolize intracranially to cause infarction.