Case Report: Role of MRI, CT, and 18F-FDG PET/CT in staging and response assessment of pediatric synovial sarcoma

Synovial sarcoma is a rare and aggressive soft tissue malignancy that predominantly affects adolescents and young adults. Early diagnosis can be challenging due to nonspecific clinical presentation and the heterogeneous imaging appearance of these tumors. Multimodal imaging plays a central role in disease detection, characterization, staging, and treatment planning, and is increasingly used for treatment response assessment. We report the case of a 16-year-old girl presenting with progressive pain and functional limitation of the right shoulder, ultimately diagnosed with a giant synovial sarcoma arising in an uncommon anatomical location. The diagnostic work-up included a comprehensive imaging approach integrating ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), and whole-body ^18F-FDG PET/CT. This multimodal strategy allowed accurate evaluation of tumor extent, assessment of possible bone involvement, and detection of regional lymph node disease. Following three cycles of combination chemotherapy with ifosfamide and doxorubicin, follow-up imaging demonstrated a reduction in tumor metabolic activity on ^18F-FDG PET/CT, consistent with an early metabolic response to therapy, despite the persistence of a relatively stable tumor volume on anatomical imaging. This case underscores the importance of an integrated imaging strategy in the management of pediatric soft tissue sarcomas and highlights the clinical value of combining complementary imaging techniques in rare and complex presentations. In particular, it illustrates how the coordinated use of multiple diagnostic modalities can optimize staging accuracy and support individualized treatment planning in pediatric patients with uncommon and large soft tissue tumors.