HISTOPATHOLOGICAL FEATURES OF IN-SITU VEIN BYPASS STENOSES

Objectives: To analyse the histopathological features of in situ vein bypass stenoses. Materials and Methods: Nineteen specimens of primary (n=16) or recurrent (n=3) vein graft stenoses obtained from 17 patient s during surgical revision were prepared for light microscopy and immu nohistochemical investigation. The median time interval from bypass su rgery to stenosis excision was 5 months (range 2-52 months). Twenty-se ven saphenous vein segments obtained from patients undergoing primary bypass surgery served as controls. Results: Graft stenoses were charac terised by moderate to severe intimal hyperplasia composed of actin po sitive but desmin negative cells, interspersed with areas of fibrosis. A single layer of factor VIII positive endothelial cells were identif ied on the luminal surface. The media, separated from the intima by a poorly defined elastic lamina, usually appeared normal or mildly hyper plastic and consisted of smooth muscle cells, which stained positive f or actin as well as for desmin. The adventitia was composed of loose c onnective tissue in which lymphocytes, plasma cells and giant cells we re occasionally seen. Atheromatous material was absent from intragraft lesions, but was observed in one specimen, which teas harvested from a proximal anastomotic lesion. The majority of pre-bypass vein segment s showed evidence of intimal thickening whereas medial hyperplasia was less common. Conclusions: Ln situ vein bypass stenoses mainly consist ed of intimal hyperplasia and varying degrees of fibrosis. Similar but less pronounced morphological changes were found in pre-bypass vein s egments. The nature of the actin positive but desmin and factor VIII n egative intima cells is uncertain, and further studies are needed to c haracterise this cell type.