The goal of this clinical trial is to evaluate the safety and feasibility of the Cygnum Aneurysm Sac Management Device in patients with abdominal aortic aneurysms treated with endovascular aneurysm repair (EVAR). The main questions it aims to answer are:

1. Is the Cygnum device safe when used adjunctively with standard EVAR endografts?
2. Does it effectively reduce or prevent type II endoleaks by managing the aneurysm sac?

Participants will:

1. Undergo EVAR with adjunctive implantation of the Cygnum device
2. Have follow-up imaging (e.g., CT scans) and clinical assessments to evaluate device position and sac behavior over time

Inclusion Criteria:

• Patient can understand the purpose of the trial, voluntarily participate in the trial and sign the informed consent
• Patient is willing to complete the follow-up according to the requirements of the protocol.
• Patient AAA anatomy complies with "instructions for use" for commercial EVAR devices used
• ≥18 years old
• Abdominal aortic aneurysm with sac diameter ≥ 5.5cm in males and ≥ 5.0cm in females
• Maximum blood flow luminal diameter ≤ 50mm
• Eligible for endovascular aneurysm repair based on anatomical considerations, such as adequate iliac/femoral access
• Patient is American Society of Anesthesiology (ASA) grade 1 through 3, inclusive.

Exclusion Criteria:

• Concomitant Common Iliac Artery aneurysms ≥ 25mm
• Life expectancy <2 years
• Already participating in an investigational drug or device study
• Known allergy or contraindication to any study device material
• Coagulopathy or uncontrolled bleeding disorder
• Ruptured, leaking, inflammatory or mycotic aneurysm
• Connective tissue diseases (e.g., Marfan Syndrome)
• Unsuitable vascular anatomy that may interfere with device introduction or deployment, in the opinion of the investigator
• Aneurysmal or dissected disease of the descending thoracic aorta
• Previous surgical or EVAR repair for AAA
• Myocardial infarction and/or major heart surgery ≤ 90 days prior to the procedure
• Transient Ischemic Attack or stroke ≤ 90 days prior to the procedure
• Unstable angina or other active cardiac condition such as congestive heart failure, untreated or worsening atrial arrhythmia, ventricular arrhythmia or valvular disease ≤ 30 days prior to the procedure
• Unable or unwilling to comply with study follow-up requirements
• Serum creatinine level ≥ 180 µmol/L
• Patients of childbearing potential who are pregnant or planning to become pregnant during the course of the study
• Patient has other medical, social or psychological problems that, in the opinion of the investigator, study involvement would not be in their best interest.