The ultrastructure of mucoid "onionskin" intimal lesions in malignant nephrosclerosis

The ultrastructure of mucoid "onionskin" intimal thickening in the intrarenal arteries was studied in 12 cases of malignant hypertension. The thickened areas were found to contain proliferating myointimal cells, basement membrane lamellas, and ruthenium-red--positive proteoglycans. The proteoglycans consisted of granules 15--35 nm in diameter and thin filaments about 3 nm thick. The filaments connected the granules to each other and to the basement membranes of the concentric lamellas, to the basement membranes of the endothelial and myointimal cells, and also to the cell surfaces. This arrangement imparted a loose meshwork pattern to the mucoid layer. The granulofilamentous material is considered to be a structural component of the pathologic lesion distinct from plasma insudation. The relationship between the intercellular substances and the myointimal cells is briefly discussed.