The persistent embryonic vein in Klippel-Trenaunay syndrome.

Klippel-Trenaunay syndrome (KTS) is a congenital malformation syndrome with prominent vascular anomalies. A persistent embryonic vein (PEV) may be located on the affected leg(s) of patients with KTS. Our understanding of PEVs of the legs is limited and their nomenclature is confusing. The objective of this study was to obtain further insight in the prevalence, nomenclature and etiology of PEVs of the legs in KTS and to propose a standardized description of anomalous leg veins in KTS. We investigated 70 KTS patients for the presence of PEVs (lateral marginal vein, LMV) of the legs by duplex ultrasonography. We performed histopathological analysis of a surgically excised PEV (LMV) of a typical KTS patient, and we conducted an extensive literature study. Duplex ultrasonography showed LMVs in 12/70 (17.1%) patients. The terms used to describe PEVs in the leg are quite variable, while indicating only two types: lateral marginal vein (LMV) and persistent sciatic vein (PSV). The histology of the excised LMV showed remarkable similarity with that of varicose veins found in the general population. In conclusion, the prevalence of LMVs in our KTS cohort is 17.1%. Two PEVs can be found in the legs and we propose nomenclature based on anatomical criteria, thereby using only the terms persistent lateral marginal vein and persistent sciatic vein, combined with the patency of the deep venous system. We hypothesize that PEVs are most likely caused by a genetic defect leading to abnormal venous pattern formation, which is further supported by our histopathological findings.