The ultrastructure of the reaction of arterial walls to cholesterol crystals in atheroembolism.

Scanning electron microscopy of atheromatous material revealed flat rhombic cholesterol crystals piled one upon the other. The fate of cholesterol crystals in the atheromatous material was followed after injection intra-arterially into the left renal arteries and left common carotid arteries of rabbits. The lipid and membranous component of the atheromatous material disappeared from the lumen of the vessels in 2-3 days after injection. Macrophages engulfed small cholesterol crystals and exposed surfaces attracted a layer of platelets. Larger cholesterol crystals evoked a giant cell response while within the lumen. Some cholesterol crystals penetrated the vessel walls or were included in the vessel wall reaction and induced a covering of endothelial cells sequestrating them from the lumen. The cholesterol crystals contained in some of the macrophages showed fracture lines and in some instances there were associated myelin figures. Large cholesterol crystals eventually elicited a fibroblastic response from the vessel wall (at about 1-4 weeks after injection) which could give rise to partial or almost complete occlusion of the vessel lumen.