Unusual Isolated Thymic Relapse of Neuroblastoma Detected By 123I-mIBG Scintigraphy in a Pediatric Patient.

Neuroblastoma (NB) is the most common extracranial solid malignancy of childhood, arising from neural crest cells of the sympathetic nervous system. Metastatic spread most frequently involves the bone marrow, bones, lymph nodes, and liver, whereas soft-tissue, central nervous system, and pulmonary metastases are less common. Unusual sites of recurrence may present a significant diagnostic challenge. We report a rare case of thymic relapse of NB presenting as an anterior mediastinal mass with intense uptake on 123I-meta-iodobenzylguanidine (123I-mIBG) scintigraphy. This case highlights an uncommon pattern of NB recurrence and the value of 123I-mIBG imaging in its detection.