A novel Doppler ultrasound approach for phenotypic assessment and follow-up of Klippel-Trénaunay syndrome: A retrospective multicenter study

Background Klippel-Trénaunay syndrome (KTS) is a rare congenital vascular malformation disorder involving complex venous, lymphatic, and soft-tissue abnormalities. Doppler ultrasound (DUS) is widely used for vascular assessment, but the relationship between ultrasound-derived features and venous clinical severity in KTS remains insufficiently defined. Methods This retrospective multicenter study included 58 patients with clinically diagnosed KTS involving 63 affected lower extremities between January 2020 and December 2022. We evaluated whether selected DUS-derived features were associated with venous clinical severity assessed using CEAP class and VCSS. Associations were analyzed using Kendall’s tau-b correlation and exploratory generalized additive models. Results Deep venous anomalies were identified in 25 of 63 affected extremities (39.7%). The LMV was detected in 60 extremities (95.2%), with a mean diameter of 5.23 mm. Posture-dependent venous caliber or visualization changes were observed in nine extremities (14.3%). VCSS increased across CEAP classes ( p < .001). LMV diameter showed a moderate positive correlation with VCSS (tau = 0.338, p < .001). In the exploratory GAM, LMV diameter showed a possible nonlinear association with VCSS, with higher scores observed around and above an approximately 5-mm reference point ( p = .049). Morphologic lymphatic malformation was also associated with higher VCSS after adjustment for model covariates (beta = 2.23, p = .020). Conclusions DUS-derived features, particularly LMV diameter and morphologic lymphatic malformation, were associated with venous clinical severity in lower-limb KTS. Supine-standing DUS additionally demonstrated posture-dependent venous caliber or visualization changes in a subset of extremities. These findings support standardized DUS as a useful imaging approach for phenotypic assessment and follow-up in KTS, while the exploratory LMV diameter reference point requires prospective validation.