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.

The authors have declared no competing interest.

A one-year license of EndoSize (Therenva) and A4clinics Research Edition (Vascops) was funded by the German Heart Foundation (Deutsche Herzstiftung) with a grant given to A Busch (F/46/18).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study was performed in accordance with the declaration of Helsinki and tissue sampling was approved by the local ethics committees of the individual centers (Ethikkommission Klinikum rechts der Isar: 2799/10; Ethikkommission Duesseldorf: 2019-578; Ethikkommission Wuerzburg: 188/11; Ethikkommission Wien: Ref 1729/2014). The HistAAA study was specifically approved for the leading center (Ethikkommission Klinikum rechts der Isar: 576/18S).

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Yes

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All data produced in the present work are contained in the manuscript