Primary B-cell lymphoma of the pelvic bone in a young patient: Imaging features of a rare case

Bone scan of an 18-year-old male who initially presented with chronic left knee pain showed increased radiotracer uptake in the left knee indicative of osteoarthritis. For the incidental finding of diffusely intense uptake involving the left hemipelvis, Paget’s disease was favored over osteosarcoma and Ewing’s sarcoma. CT scan without IV contrast showed cortical and trabecular thickening of the hemipelvis. However, it was not until the MRI study that showed findings inconsistent with Paget’s disease and suspected primary bone lymphoma because of the extensive T1 signal loss due to bone marrow replacement with contrast enhancing soft tissue in the absence of cortical bone destruction, with histopathology revealing extranodal diffuse large B-cell lymphoma. We present a rare case of Non-Hodgkin’s lymphoma occurred in a young patient and illustrate the diagnostic difficulty of primary bone lymphoma as well as emphasize the importance of multi-modality correlation for the differential diagnosis of Paget’s disease vs. primary bone lymphoma.