Role of the endothelial lining in persistence of residual lesions and growth of recurrences after endovascular treatment of experimental aneurysms.

BACKGROUND AND PURPOSE We sought to investigate the role of the endothelial lining in aneurysmal persistence and recurrence after endovascular treatment of aneurysms. METHODS Bilateral venous pouch canine carotid aneurysms were studied by angiography and pathology 1, 2, and 3 weeks after intraoperative collagen sponge embolization, coated or not coated with fibrinogen (n=15). In 12 dogs the endothelial lining of one aneurysm was removed before embolization, and results were compared with a control aneurysm after bilateral sponge embolization. In 4 animals embolization with a sponge covered with endothelium was compared with treatment with a sponge covered with adventitia. In 4 animals an inverted venous pouch aneurysm embolized with an adventitia-covered sponge was compared with a normal aneurysm embolized with an endothelialized sponge. In 3 animals inverted venous pouch aneurysms were embolized with a sponge covered or not covered with endothelium. Control aneurysms (n=3 or 4 each) included untreated normal, inverted, and de-endothelialized venous pouch aneurysms. Angiographic results at 3 weeks were compared by Wilcoxon's test. RESULTS Endothelialization of the clot that forms on the sponge was complete at 1 week, forming clefts that developed into recurrences. Reversed or de-endothelialized aneurysms spontaneously thrombosed, while normal venous pouch aneurysms remained patent for at least 3 weeks. The addition of fibrinogen, endothelium, or adventitia to the sponges did not prevent recurrences, which occurred routinely after embolization of endothelialized aneurysm. De-endothelialization of the aneurysmal wall improved angiographic results at 3 weeks (P=0.02), while reversing the venous pouch before embolization led to complete healing (P=0.003). CONCLUSIONS The endothelial lining is essential to the persistence of residual lesions. Early endothelial invasion of the clot leads to recanalization and recurrences after embolization of aneurysms. This observation provides new opportunities to improve results of endovascular treatment of aneurysms.