Soft tissue masses in children: An important differential diagnosis

Fariba Williams, Mitesh Naik, Derek Roebuck, Great Ormond Street Hospital for Children NHS Foundation Trust, London


Synovial sarcomas (SS) are malignant tumours arising from mesenchymal cells, and account for 10% of all sarcomas1. They most frequently occur in young adults, commonly within extremities near large joints. SS can invade locally and/or give rise to nodal or distant metastasis.

Case Report

 A 9-year-old boy, previously fit and well, presented with a week’s history of atraumatic painless swelling of the inferomedial right thigh. Their only relevant history was a strong family history of malignancy including leukaemia and breast cancer. On examination, a soft mass was palpable overlying the right lower femur, with a harder area centrally.

Initial ultrasound demonstrated a mixed echogenicity soft tissue mass measuring 11 x 6 x 5 cm, centred on the posterior compartment of the distal right thigh, displacing the hamstrings posteriorly. Hypoechoic foci were found within, though these did not return Doppler signal to indicate intralesional vessels. Small disorganised arterialised vessels were present in other areas of the mass.

 A subsequent MRI study demonstrated a lesion with a central solid component and surrounding cystic areas, some of which appeared to be blood-filled. At this point, an atypical vascular malformation was in the differential as well as a neoplastic process.

Ultrasound-guided needle biopsy confirmed a biphasic SS. PET-CT ruled out nodal and distant metastasis. Chemotherapy was instituted prior to considering surgery, which may include amputation for local control.


Synovial sarcomas can be misdiagnosed as benign pathology due to their insidious onset and well-circumscribed appearance. On sonographic assessment, certain features can overlap with those found in vascular malformations or haematomas. It is important to consider SS as a differential diagnosis in children with soft tissue masses, and undertake biopsy where appropriate.


Murphey M, Gibson M, Jennings B et al. Imaging of synovial sarcoma with radiologic–pathologic correlation, Radiographics 2006; 26:1543–1565.

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