Retroperitoneal Nodal Metastasis Detected by Diffusion-Weighted Imaging in Paraspinal Alveolar Rhabdomyosarcoma

BACKGROUND: Accurate lymph node evaluation is critical in rhabdomyosarcoma, yet small or metabolically inactive nodal metastases often evade detection on conventional imaging, such as fluorodeoxyglucose-positron emission tomography-computed tomography (FDG-PET/CT). OBSERVATIONS: We report a 6-year-old girl with paraspinal alveolar rhabdomyosarcoma whose para-aortic lymph node exhibited diffusion-weighted imaging (DWI) hyperintensity but lacked FDG uptake at diagnosis. The node was interpreted as reactive and was not sampled. Nine months after first-line therapy, relapse in the same para-aortic region was histologically confirmed as nodal metastasis. CONCLUSIONS: DWI may reveal nodal metastases not identified by FDG-PET/CT or size criteria, underscoring cautious interpretation of DWI-positive, FDG-negative nodes in trunk rhabdomyosarcoma.