Morphological evaluation of the human umbilical vein graft. An experimental study

23 human umbilical vein segments (5 mm X 4-5 cm) were implanted into the carotid and iliac arteries of 15 dogs, removed at intervals ranging from 10 to 360 days after surgery and analyzed by light and scanning electron microscopy. 10 days after implantation, a thin layer of fibrin covered the central areas of the grafts, while thick platelet aggregates were found near the anastomoses. After 30 days, the progressive connective tissue ingrowth led to the organization of a thin fibrous inner layer on which endothelial-like cells grew, spreading from both anastomoses. The endothelialization process appeared to be almost complete at 120 days after implantation, while at 360 days the flow surface was totally lined.