Synovial Sarcoma in the Setting of Klippel–Trenaunay Syndrome: A Rare Case

Klippel–Trenaunay syndrome (KTS) is a rare congenital vascular disorder characterised by capillary, venous, and lymphatic malformations associated with soft-tissue and/or bony hypertrophy, predisposing affected individuals to complications such as chronic lymphoedema, bleeding, and functional impairment. Although KTS is predominantly considered a benign condition, rare malignant neoplasms, including squamous cell carcinoma, angiosarcoma, rhabdomyosarcoma, and adenocarcinoma, have been reported in affected tissues. To the best of our knowledge, synovial sarcoma arising in a KTS-affected limb has not been previously reported. This case highlights the diagnostic challenges posed by coexisting vascular malformations, which may obscure the early detection of malignant transformation, and emphasises the importance of vigilant clinical and imaging surveillance. Furthermore, it underscores the value of multimodality imaging, particularly 18F fluorodeoxyglucose positron emission tomography/computed tomography ( 18 F FDG PET/CT), in the detection, staging, and assessment of metastatic disease in synovial sarcoma arising in the setting of KTS.