False Positive of 123 I-MIBG Caused by Ectopic Thymic Rebound Hyperplasia in a Pediatric Neuroblastoma

A 6-year-old girl with high-risk neuroblastoma underwent 123 I-MIBG scintigraphy for disease surveillance, revealing abnormal radiotracer uptake in a nodule located posterior to the right lobe of the thyroid. Retrospective evaluation of prior 123 I-MIBG imaging demonstrated gradual enlargement of this lesion, accompanied by increasing 123 I-MIBG accumulation over time. Surgical excision and pathologic examination confirmed ectopic thymic hyperplasia. This case illustrates that ectopic thymic hyperplasia can lead to false-positive 123 I-MIBG uptake in pediatric patients with neuroblastoma.