(A) A whole-body FDG-PET coronal image demonstrates a hypermetabolic focus in the superior mediastinum (arrow). Physiologic laryngeal activity is noted in the midline neck (circle). (B) Axial registered PET/CT images demonstrate a sail-shaped focus of uniformly increased uptake in the anterior superior mediastinum in the location of the thymus (circle).

Differential Diagnosis

•  Benign thymic hyperplasia: Uniformly increased thymic uptake in a child following chemotherapy makes “thymic rebound” the most likely diagnosis.

•  Recurrent lymphoma: