Intracranial Carotid Artery Atherosclerosis and the Risk of Stroke in Whites

IMPORTANCE: Intracranial atherosclerosis represents a relatively unexplored, but potentially important, cause of stroke in a white population. OBJECTIVE: To investigate the relationship between intracranial carotid artery calcification (ICAC) as a marker of intracranial atherosclerosis and the risk of stroke in whites. DESIGN, SETTING, AND PARTICIPANTS: A population-based cohort study in the general community with 6 years of follow-up was conducted (the Rotterdam Study). Between 2003 and 2006, a random sample of 2323 stroke-free persons (mean age, 69.5 years) underwent computed tomography scanning to quantify ICAC volume. All participants were continuously monitored for the occurrence of stroke until January 1, 2012. EXPOSURE: Atherosclerotic calcification in the intracranial internal carotid arteries. MAIN OUTCOME AND MEASURE: Incident stroke. RESULTS: During 14,055 person-years of follow-up, 91 participants had a stroke, of which 74 were ischemic. Larger ICAC volume was related to a higher risk of stroke, independent of cardiovascular risk factors, ultrasound carotid plaque score, and calcification in other vessels (fully adjusted hazard ratio per an increase of 1 SD in ICAC volume, 1.43 95% CI, 1.04-1.96). Intracranial carotid artery calcification contributed to 75% of all strokes; for aortic arch and extracranial carotid artery calcification this incidence was only 45% and 25%, respectively. CONCLUSIONS AND RELEVANCE: Our findings establish intracranial atherosclerosis as a major risk factor for stroke in the general white population and suggest that its contribution to the proportion of all strokes may be greater than that of large-artery atherosclerosis in more proximally located vessel beds.