Histological pattern and changes in extracellular matrix in aortic dissections.

Samples from 34 patients were studied both histologically and immunocytochemically by the indirect biotin-avidin peroxidase technique to analyse the distribution of the extracellular matrix components (type IV collagen, fibronectin, types I and III collagens) in dissection of the aorta. Most showed defects in type IV collagen around medial smooth muscle cells. Defects in smooth muscle cell basement membrane were found throughout the media in cystic medial degeneration and in medionecrosis, whereas in atherosclerosis such unlabelled areas were found only above advanced atherosclerotic plaques. In aortitis other defects in the smooth muscle cell basement membrane were found in areas of inflammatory infiltrates. In all of these conditions similar defects in fibronectin expression were also found. No defects in the expression of interstitial collagens type I and III were seen in the dissecting aortas. Moreover, cystic medial degeneration, medionecrosis, and atherosclerosis were characterised by intense staining of these interstitial matrix components. In the pathogenesis of the aortic dissection local changes in the basement membranes of the medial layer may be important.