BACKGROUND: Klippel-Trenaunay syndrome (KTS) is an exceedingly rare congenital disorder attributed to a sporadic mutation in the PIK3CA gene, which impairs normal blood and lymphatic vessel development. The syndrome is classically defined by a triad of congenital features: cutaneous port-wine stains, venous malformations, and progressive limb hypertrophy. Prenatal recognition of KTS is uncommon, and its sonographic features can overlap with other congenital vascular anomalies, making early diagnosis challenging.

CASE REPORT: This report reviews 2 cases of prenatally diagnosed KTS at our institution. In both fetuses, prenatal ultrasound demonstrated marked swelling and thickening of the soft tissues within the right thigh. Within these hypertrophic soft tissues, tortuous and dilated arterial and venous channels were visualized; some veins exhibited a honeycomb-like structural pattern. Color Doppler imaging revealed abundant intralesional blood flow signals. Following induced abortion, gross anatomical examination of both fetuses disclosed reddish skin discoloration over the right lower extremity. The diagnosis of KTS was established based on concordant prenatal ultrasound findings and post-abortion macroscopic anatomical evaluation.

CONCLUSIONS: The diagnostic cornerstone of prenatal KTS lies in the sonographic detection of disproportionate soft-tissue and bony overgrowth accompanied by characteristic vascular malformations. It is equally imperative to rigorously differentiate these ultrasound findings from those of other overgrowth syndromes and vascular anomalies, and to assess for potential severe complications that may affect perinatal prognosis. An accurate prenatal diagnosis, coupled with multidisciplinary perinatal management involving obstetricians, geneticists, and neonatal specialists, is essential for optimizing pregnancy counseling and improving overall clinical outcomes.

Keywords: Diagnosis, Hypertrophy, Klippel-Trenaunay-Weber Syndrome