Evolution of Sac Filling Techniques and Concepts in Endovascular Treatment of Abdominal Aortic Aneurysm: A Narrative Review.

Endovascular aortic aneurysm repair (EVAR) has become the first-line treatment for abdominal aortic aneurysms (AAA); however, its long-term durability is affected by Type II endoleak. This narrative review describes the evolution of sac filling techniques and concepts developed to address this complication. In selected cases of diagnosed Type II endoleaks, early therapeutic sac filling, while clinically indicated, is frequently constrained by difficult access, variable success rates, and recurrence. Consequently, prophylactic sac filling during primary EVAR has been adopted as an alternative approach, with reported high technical success and reduced endoleak incidence. The subsequent Nellix Endovascular Aneurysm Sealing (EVAS) system, although early results showed technical feasibility, was associated with graft migration, endobag separation, and reintervention at long-term follow-up, leading to its withdrawal from the market. Currently, devices based on shape memory polymer (SMP) provide early observations of decreased endoleaks and sac regression. This review outlines the transition from reactive management to preventive strategies, and, more recently, to patient-specific, material-based approaches, while showcasing emerging strategies that may influence long-term EVAR outcomes. However, these novel approaches remain under investigation, and larger controlled studies with extended follow-up are required to establish their clinical utility.