Diagnostic Value and Limitations of FDG-PET for the Staging of Childhood Lymphomas.

Positron emission tomography with fluorine-18-fluorodeoxyglucose (FDG-PET) has the potential to detect malignant cells by their increased glycolysis. PET can detect early changes, before they are apparent on anatomic imaging. Whole-body PET can also detect lesions at unexpected sites. However, physiologic FDG uptake in non-malignant conditions limits the specificity of PET. PET is predominantly used in adult lymphoma patients, limited number of studies were published dealing with PET and PET/CT in childhood lymphomas. The aim of our study was to assess the usefulness of PET for initial staging of pediatric lymphomas and to evaluate benign pathologic causes of FDG uptake.

Over a period of 5 years 86 children and adolescents with lymphoma (58 with Hodgkin's lymphoma, 28 with non-Hodgkin's lymphoma) had complete staging work-up including FDG-PET or PET/CT and were included into this prospective study. Patients were aged 4-19 years, 57 (66%) were boys. No patient had CNS lymphoma infiltration. PET findings were correlated with conventional staging methods (CSM) including CT, ultrasound, and bone marrow examination. Discordant findings were verified by MRI and follow-up radiographic studies including PET.

PET revealed 40 additional lymphoma manifestations in 34% (26/86) of studies and correctly upstaged 15% (13/86) of patients. Only 2% (2/86) of children were not accurately staged by PET, when PET failed to visualize diffuse bone marrow infiltration (extent of 15% cells) in 1 patient, and missed small pulmonary metastases (≤6 mm) in 1 child. Compared with CSM, PET had significantly higher sensitivity (97% vs. 83%), specificity (100% vs. 89%), and significantly higher accuracy (98% vs. 84%). Physiologic thymic FDG uptake was observed in 15% (13) of patients; diffuse increased FDG bone marrow activity had 22% (19) of children, and intense FDG activity in fatty tissue occurred only in 8% (7) of patients.

PET imaging was highly sensitive in detecting all subtypes of pediatric lymphomas and has potential to accurately define the disease stage except the lungs, where CT has excellent sensitivity. Understanding of the physiologic FDG biodistribution and benign pathologic causes of FDG uptake is essential for accurate scan interpretation.

Supported by grants: IGA NS/9997-4, NS/10480-3, MSM 0021620813 and MZO FNM 2005

No relevant conflicts of interest to declare.