Abstract 3829: Extraluminal Protruding Plaques in Intracranial Arteries. An angiographic and pathological analysis of Circle of Willis specimens from the Nun Study

Abstract

BACKGROUND There is little data about extraluminal protruding plaques in intracranial arteries. Such plaques may not cause luminal stenosis and may be undetectable by standard angiographic modalities. It is important to identify the prevalence of such plaques because these plaques may be a cause of thrombosis and ischemic events in patients with cryptogenic strokes. OBJECTIVE To identify the prevalence of extraluminal protruding plaques in intracranial arteries from autopsy specimens of Nun Study. METHODS A random sample of 54 specimens was selected from Nun Study repository of post-mortem intracranial arteries (Circle of Willis). The Nun Study is a longitudinal study of aging and Alzheimer's disease funded by the National Institute on Aging including 678 participants who are 75 to 106 years of age. Basilar artery and proximal middle cerebral arteries were inspected and arteries with plaques were identified. The specimens were placed in a liquid container and an angiographic catheter was placed in vessel of interest. Using iodinated contrast media and Ziehm Vista C-arm, angiography was obtained in multiple planes. Percentage luminal stenosis was measured using normal proximal or distal segment of the vessel as reference. Using microscopic images, extraluminal protruding plaques was then sequentially measured. Percentage increase in extraluminal wall diameter was calculated as (extraluminal diameter at plaque site - normal diameter)/normal diameter x100. RESULTS Out of 162 samples, plaques were identified in 126 samples. The characteristics of the plaques are tabulated. The percentage increase in extraluminal wall diameter was 10.33 ± 8.13. For vessel with angiographically occult plaques, the percentage increase in extraluminal wall diameter was 9.2±3.2. In extraluminal protruding plaques, the median protrusion was 0.3 mm and maximum protrusion was 0.9 mm. There was no difference between the percentage extraluminal protrusion between the middle cerebral (0.3±0.1) and basilar artery plaques (0.36±0.2), p=0.8. The frequency of extraluminal plaques without angiographic stenosis of any severity was higher than extraluminal plaques with angiographic stenosis (52% and 56% for middle cerebral artery and basilar artery, respectively). CONCLUSIONS There appears to be a high prevalence of extraluminal protruding plaques among elderly persons and most of these plaques are not detected by angiography. Newer, imaging modalities like vessel wall high resolution visusalization by magnetic resonance imaging may help identify the prevalencc and ischemic event risk associated with such plaques.