Abdominal aortic aneurysms’ histomorphology differs on the individual patient level and is not associated with classic risk factors – the HistAAA study

Abstract

Objective: Abdominal aortic aneurysm (AAA) treatment is upon a diameter threshold by open (OAR) or endovascular aortic repair. Attempts for medical growth abrogation have failed. This study aims to elucidate the heterogeneity of AAA based on histomorphology in correlation to individual patient data and aneurysm metrics. Patients and Methods: Aneurysm samples from the left anterior wall from four university center biobanks underwent histologic analysis including angiogenesis, calcification, fibrosis, type and grade of inflammation in adventitia and media. Clinical information included age, comorbidities, etc. as well as type of aneurysm (intact, symptomatic, ruptured, inflammatory). Aneurysm morphology included diameter and semi-automated geometric analysis using Endosize (Therenva) segmentation. Additionally, aneurysm growth was assessed. Results: 364 patient samples (85.4% male, median age 69 years) demonstrated acute (mix/granulocytes) or chronic (monocytes/plasma cells) type inflammation and score, coherent in adventitia and media (p < 0.001), not associated with the type of aneurysm (52x ruptured; 37x symptomatic; p = 0.51) or diameter (57 [52-69] mm; p = 0.87). The degree of fibrosis and the presence of angiogenesis were significantly higher (both p < 0.001) with increasing inflammation score, which significantly decreased with patient age (est = - 0.015/year, p = 0.017). No significant differences in inflammation, fibrosis or angiogenesis were seen for ruptured (vs. intact), acute (vs. elective), male (vs. female) of diabetic (vs. non) patients, while current smoking was associated with more chronic inflammation (p = 0.007) and a higher degree of fibrosis (p = 0.03). Aneurysm geometric morphology (n=252) or differing annual growth rates (n=142) were not significantly associated with histologic characteristics. Conclusion: Type and degree of inflammation are the most distinguishable histologic characteristics in the AAA wall between individual patients. Despite the association to age and smoking status, no significant correlation to any patient or aneurysm specific feature, especially not diameter or rupture exists.