Background: Peripheral arterial abnormalities (PAA) are increasingly recognized in heritable thoracic aortic disease (HTAD), yet no standardized definitions or imaging protocols exist. This heterogeneity limits clinical interpretation, longitudinal follow-up, and comparability across studies. We conducted a French national Delphi consensus to establish uniform criteria for the identification, classification, and measurement of PAA in Marfan syndrome (MFS) and related HTAD.

Methods: A two-round modified Delphi process was completed by national experts in vascular medicine, radiology, and cardiology. Round 1 addressed definitions, reference diameter selection, tortuosity assessment, and imaging methodology. Round 2 refined key items based on qualitative feedback. Strong consensus was predefined as ≥85% agreement.

Results: Of 45 invited experts, 22 responded to Round 1 (49% response rate) and 18 completed Round 2 (82% retention). Strong consensus was reached for standardized definitions of aneurysm. Strong consensus was reached for standardized definitions of aneurysm (focal dilatation ≥150% of reference diameter), ectasia (125–149%), mega-artery (diffuse non-focal dilatation ≥150% of reference diameter), and arterial tortuosity (≥2 inflexions). A hierarchical reference diameter approach was validated, prioritizing the adjacent non-pathological segment, followed by the contralateral artery and population-based norms. Perpendicular measurement to the vessel axis achieved unanimous agreement (100%). The term tortuosity was preferred over dolichoartery (89%). Divergent opinions persisted regarding ultrasound measurement technique, leading to pragmatic recommendations aligned with existing aortic imaging practices.

Conclusions: This French national Delphi consensus provides a standardized framework for defining and assessing PAA in MFS and related HTAD. The harmonized terminology and imaging recommendations will enhance diagnostic consistency, facilitate multicentre research, and support integration of PAA into comprehensive vascular evaluation within specialized HTAD care networks.