Human intracranial atherosclerosis. A histochemical and ultrastructural study of gross fatty steak lesions.

A descriptive study of atherosclerotic lesions in human intracranial arteries was undertaken using both light and electron microscopic technics. Arterial segments of human middle cerebral, internal carotid and basilar arteries with gross fatty streak lesions were obtained at autopsy within 4 hours after death, fixed and embedded in plastic. A new technic has been developed in which 0.5 mu-thick sections can be stained with PAS/alcian blue, thereby enabling clear differentiation, substantiated by simultaneous electron microscopic studies, between the lipid-filled smooth muscle cell, which is surrounded by a PAS-positive basement membrane, and the lipid-filled blood monocyte. These technics demonstrated that the gross fatty streak comprised a focal intimal thickening bordered on the lumen by a patent endothelial lining and on the media by a usually intact elastic membrane. The lesion contained smooth muscle cells and cells presumed to be blood monocytes, both filled with and devoid of lipid droplets. Although little fragmented or new elastica was found in the extracellular space, numerous foci of membranous material could be observed, believed to be cell debris and plasma lipoproteins. The similarity between the morphology of such lesions in intracranial arteries with those found in other arterial beds suggests that the documented differences in the prevalence of atherosclerosis in the various beds has no bearing on either the structure of each type of lesion or its progression.