Plantar synovial sarcoma mimicking a vascular malformation in a child: a clinicopathologic case report

Hypervascular plantar soft-tissue lesions in children may be misinterpreted as benign vascular abnormalities, particularly when Doppler ultrasound shows marked internal vascularity. We report a 12-year-old boy with a painful plantar foot mass initially considered a hemangioma or low-flow vascular malformation on ultrasound and MRI. Although imaging demonstrated prominent vascularity and enhancement, the lesion was predominantly solid, showed irregular enhancement and partially ill-defined margins, and lacked typical serpiginous morphology or definite flow voids. Image-guided biopsy revealed a malignant spindle-cell neoplasm. Histology showed an infiltrative monophasic spindle-cell tumor involving adjacent soft tissues, and immunohistochemistry demonstrated focal cytokeratin AE1/AE3 expression, multifocal EMA positivity, and strong diffuse nuclear SS18 staining, supporting synovial sarcoma. The patient underwent limb-sparing resection after multidisciplinary evaluation. This case emphasizes the importance of pathologic confirmation before vascular-directed intervention.