The role of FDG PET/CT in staging and restaging primary bone lymphoma

Objectives: Primary bone lymphoma (PBL) is one of the rarest primary bone malignancies. Very limited data are available about the role of FDG PET/CT in PBL.

Methods: 16 relevant patients had FDG PET/CT for staging or staging/restaging PBL. The cases with extraskeletal lesions such as lymphadenopathy or with osseous involvements in disseminated lymphoma were excluded based on the definition of PBL. FDG PET/CT findings were correlated to pathologic and/or anatomic image information.

Results: FDG PET/CT was positive with markedly increased uptake in all known PBL lesions, with a sensitivity of 100%. In 15/16 (93.8%) cases, the bone lesions infiltrated the adjacent soft tissue with visible soft tissue components. Except for known primary bone lesion, FDG PET/CT showed additional 24 bone lesions in 7 patient, which accounted for 44% of all cases. With SUV_max 2.5 as a cutoff for differentiating residual lymphoma from metabolically inactive disease on restaging scan, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of FDG PET/CT for PBL were 100% (4/4), 75% (9/12), 57% (4/7) and 100% (9/9), respectively. The diagnostic accuracy of restaging FDG PET/CT was 81% (13/16). 2 of 3 false positive scans were due to post-therapeutic osteonecrosis.

Conclusion: FDG PET/CT is sensitive for demonstrating PBL which is typically highly FDG avid, and has the ability to depict extraskeletal soft tissue involvement and additional bone lesions on staging. More importantly, FDG PET/CT may accurately and reliably evaluate therapeutic response with excellent sensitivity and NPV. However, false positive FDG uptake poses a concern on restaging PET/CT. Posttherapeutic osteonecrosis is a potential source of false positive findings on FDG PET/CT.