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FIG 4. Electron micrographs of nidus vessels in the acute AVM model (ie, of normal rete mirabile microvessels) (A) and in the 2-month-old AVM model (B). L indicates vessel lumen. Original magnifications x7500.
A, Note the normal and variably prominent endothelium. Smooth muscle cells (arrows) are immediately deep to the internal elastic lamina.
B, Note thinning and attenuation of the endothelium with focal breaks in the endothelial barrier (straight arrows). Underlying fibromuscular hyperplasia is noted with prominent smooth muscle and fibroblast cells, which are separated by bands of collagen and granular and fibrillar material, probably representing glycosaminoglycans. Curved arrow indicates a focus in which the internal elastic lamina is attenuated.
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