Cellular content and permeability of intraluminal thrombus in abdominal aortic aneurysm

Purpose: A pathologic feature commonly associated with abdominal aortic aneurysms is the presence of variably sized and shaped intraluminal thrombus, which may be fundamental to the disease process. However, the precise role of the intraluminal thrombus in the formation, enlargement, and rupture of abdominal aortic aneurysms is unknown. The hypothesis tested in this study was whether there were structural features of aortic thrombi to suggest that it may be involved in the pathogenesis of abdominal aortic aneurysms. We have investigated this hypothesis using a variety of structural and biochemical techniques. Methods: Tests performed were light, transmission, and scanning electron microscopy; fluid permeability measurements; and Western blots. Results: Intraluminal thrombus found in abdominal aortic aneurysms is structurally complex and is traversed from the luminal to abluminal surface by a continuous network of interconnected canaliculi. Quantitative microscopic analysis of the thrombus shows cellular penetration for at least 1 cm from the luminal surface of the thrombus. Macromolecular penetration may be unrestricted throughout the entire thickness of the thrombus. Fibrin deposition occurred throughout the thrombus, whereas fibrin degradation occurred principally at the abluminal surface. Conclusions: These principally structural studies support the hypothesis that the thrombus is a self-sustaining entity that may have significance in the pathophysiologic mechanism of abdominal aortic aneurysms.