Metabolic or molecular imaging with fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) has emerged as a powerful imaging modality for diagnosis, staging, and therapy monitoring of a variety of cancers. The accuracy of FDG-PET as an imaging tool for the primary staging of lymphoma suffers from the absence of a reference criterion to which all imaging modalities can be compared. For ethical reasons, pathological diagnosis is usually not possible for all of the lesions and abnormalities found. In this article, the current state of the art for staging of primary lymphoma is reviewed and the implications for staging and the impact on patient management discussed. Whole-body PET using FDG is superior to conventional staging, i.e., physical examination, laboratory tests, plain radiography, and CT, by 10-20%. The sensitivity of FDG-PET varies for different regions of the body and appears lowest for infradiaphragmatic disease involvement. Staging with metabolic imaging leads in 10-40% of patients to a change in clinical stage. Highly variable results have been reported on whether up- or downstaging of lymphoma with PET leads to changes in the therapeutic approach for primary lymphoma.
