Not such a simple cyst: unusual presentation of sarcoma

A 10-year-old girl presented with a lump on her left upper anterior thigh. She presented to accident and emergency twice and to her general practitioner once. It was provisionally diagnosed as a cyst but it continued to grow in size. The lump had been noticed for 6 months, in paediatric clinic it was 5×5 cm, firm, tense and felt cystic. Systemically she was otherwise well. The overlying skin was blueish with prominent veins. The MRI also suggested a cyst but on excision it was revealed to be a high-grade sarcoma. After surgical excision she had a skin graft. Regular follow-ups with MRI have not shown any recurrence, she also has regular chest X-rays which have all been normal.