Conditions that involve the vessels that supply the brain with blood have traditionally been divided anatomically into lesions that involve the extracranial large arteries and the intracranial large and small arteries. The rationale for this classification is that conditions that affect the large arteries within the neck and those that involve the large arteries in the head have somewhat different demographic, epidemiologic, and risk factor predilections and are often managed differently. Lesions in the small arteries are quite different morphologically from those in the large arteries and their epidemiologic factors and causes, as well as treatments, differ from conditions that affect the large arteries.
Caplan LR. The Effect of Small Artery Disease on the Occurrence and Management of Large Artery Disease. JAMA Neurol. 2016;73(1):19-20. doi:10.1001/jamaneurol.2015.3535