Extramedullary Hematopoiesis in Treated Diffuse Large B-Cell Lymphoma of Bone

A 65-year-old man with a history of diffuse large B-cell bone lymphoma of the right radius underwent an interim FDG PET/CT after 2 cycles of chemotherapy. Besides a complete metabolic response on the primary site, images revealed a hypermetabolic nodule in the posterior mediastinum, not present on the initial images. The metabolic activity of the nodule was similar to that of the reactive bone marrow and disappeared, concomitantly to the normalization of the medullar signal on the posttreatment images. The similarity and synchronous metabolic activity evolution in the nodule and bone marrow indicate extramedullary hematopoiesis.