Histological characterisation of intraluminal thrombi from patients with abdominal aortic aneurysm

Introduction An abdominal aortic aneurysm (AAA) is a cardiovascular disease characterised by a progressive pathophysiological dilatation of the infrarenal part of the aorta [ 1 ]. The main events of AAA pathology are chronic inflammation as well as extracellular matrix (ECM) degradation, leading to the progressive remodelling of the aortic wall [ 2 ]. Recently, platelets were found to be crucial for AAA formation by modulating ECM remodelling and chronic inflammation, by using the porcine pancreatic elastase (PPE) perfusion model [ 3 ]. Another important feature of human AAA pathology is the formation of an intraluminal thrombus (ILT), which is present in about 75% of all AAA patients [ 4 ]. Thereby, the complex and inhomogenous structure of the ILTs makes it difficult to understand their role in AAA formation and progression [ 5 ] [ 6 ]. Considering that rupture represents the most dangerous complication in the AAA pathology, a detailed analysis and better understanding of ILT composition including its role in AAA pathogenesis, may enhance future rupture risk assessment. Therefore, we characterised the structure of human ILTs obtained from patients with AAA and peripheral thrombi obtained from patients during thrombectomy of acutely thrombosed vessels. Method Martius Scarlet Blue stain, Masson’s Trichrome stain, Picrosirius red stain, Feulgen stain, Immunohistochemical (IHC) staining Results In general, the intraluminal and peripheral thrombi showed a great heterogeneity. More specifically, the luminal layer of intraluminal thrombi was found to contain a variety of cell types, including RBCs, platelets, vWF, and leukocytes, all embedded within a fibrin meshwork. In the medial/abluminal layer, platelets and leukocytes were highly abundant, with leukocytes preferentially accumulating around platelet-rich regions. Furthermore, the ILT contained abundant von Willebrand factor (vWF) from the lumen to the aortic wall, present both in platelet-rich regions and in areas lacking platelets. As dense fibrin structures are surrounded by platelet-rich regions and aligned with vWF, these three components appear to be closely interrelated. In addition, extracellular DNA, cholesterol crystals, and collagen were detected within the ILT tissue. Peripheral arterial thrombi can be classified into red, intermediate, and white sections, primarily composed of RBCs, platelets, or a combination of both, with all sections showing only minimal fibrin staining. Therefore, peripheral arterial thrombi contain extracellular DNA and abundant amounts of vWF. Conclusion In conclusion, intraluminal and peripheral thrombi display marked heterogeneity, with ILTs showing organised layers rich in platelets, leukocytes, and vWF, alongside fibrin, extracellular DNA, cholesterol crystals, and collagen. These findings suggest a complex interplay between platelets, fibrin, and other thrombus components that may influence AAA pathogenesis, thrombus stability and risk of rupture. Publication History Article published online: 17 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany