Deterioration of in-situ vein bypasses: anatomic study of 11 cases.

During the follow-up of 130 patients with in-situ bypasses 11 patients were reoperated following the detection of degenerative changes. The lesions found included anastomotic aneurysms (1), diffuse dilatation (2), localized aneurysms (5), stenosis of valve sites (2), and diffuse narrowing (1). The mean interval for the onset of a lesion was eight months. Histologic findings showed fibrous thickening of the intima, replacements of myocytes by collagen in the media, and moderate adventitial fibrosis. With some quantitative differences these changes are similar to those reported in reversed vein bypasses. It is therefore concluded that devascularization of the adventitia, as happens in reversed bypasses, is not an important etiology in the development of degenerative changes. The better patency rate reported for in-situ bypasses is the result of hemodynamic factors, but not because in-situ bypasses are protected from degenerative changes by their intact adventitial supply.