Patterns of pannus growth of the expanded polytetrafluoroethylene vascular graft with special attention to the intimal hyperplasia formation

Serial histologic observations of the healing process of expanded polytetrafluoroethylene (PTFE) vascular grafts in dogs were performed. The common iliac arteries of 12 mongrel dogs were replaced with a 2-cm segment of 6 mm PTFE graft, bilaterally. The grafts were studied microscopically after the animals were killed at 4, 8, 12, 16, 20, and 24 weeks. All the grafts remained patent up to 24 weeks. Special attention was paid to the histological characteristics of pannus growth, which were divided into two types: smooth appearing and irregular. The former type was characterized by smooth, thinner connective tissue growth along the graft, and the latter was defined as irregular-shaped pannus containing large and small thrombi. Only pannus of the smooth type showed similar growth patterns and growth rates. These findings suggest essentially that pannus develops smoothly from both ends of the graft; however, thrombi disturbed this growth pattern. In 24 grafts, eight nodular lesions of the pannus (>500 μ in height) were found; five distally and three proximally. All eight lesions were found within 3 mm of the anastomoses. Among these eight lesions, five were on the completely healed pannus, and the remainings were all on the irregular pannus. This suggests that thrombi organization followed by nodular lesions are major offending factors that lead to the formation of intimal hyperplasia.