Evaluation of a new self-expandable silicone stent in an experimental tracheal stenosis

Study objectives: To assess the usefulness of an animal model for testing new tracheobronchial stents. Setting: Animal laboratory of a university hospital. Animals and interventions: In a series with 12 mini-pigs, we induced a stable fibromalacic tracheal stenosis that was 50% to 70% of the normal tracheal diameter. After dilation we inserted a 16 x 40-mm self-expandable silicone stent into the stenotic part of the trachea in 10 of the mini-pigs. Five of the stents had a smooth outer surface, and five had additional silicone retaining spikes. Because of a long stenosis in two of the mini-pigs, two overlapping stents tone smooth and one with spikes) were inserted. Measurements and results: Stent deployment was successful and resulted in the disappearance of the slight to moderate strider in all of the mini-pigs. Over a mean (+/- SD) observation period of 24 days (range, 10 to 41 days), all of the mini-pigs redeveloped strider. Three of them died unexpectedly of suffocation: in all three a smooth stent had mi,orated, leading to total obstruction of the stenosis. In total, five of the six smooth stents migrated, and only one of the six spiked stents migrated. There was considerable granulation tissue formation at the ends of all of the stents. In the two control mini-pigs, a 12 x 35-mm Dumon stent was inserted. Both Dumon stents migrated, and one of them had considerable granuloma formation at its ends. At the end of the observation period, all stents were removed endoscopically and were found not to have deteriorated over time, Conclusions: Our model proved to be suitable for the evaluation of the technical aspects of the Polyflex stent, Spikes on the outer stent surface are more effective in preventing migration than smooth-surface stents. Long-term compatibility, however, seems to be difficult to test with our model because both the Bob-flex and the Dumon stents had excessive granulation tissue formation at both ends, a factor which-in the case of the Dumon stent-does not occur to such a degree in benign human airway stenoses. Our results indicate a need for prospective long-term studies in benign human airway stenoses.