Brain and whole-body FDG-PET in diagnosis, treatment monitoring and long-term follow-up of primary CNS lymphoma

Introduction: Positron emission tomography (PET) with F-18-labeled fluorodeoxyglucose (FDG) provides remarkable accuracy in detection, treatment monitoring and follow-up of systemic malignant lymphoma. Its value in the management of patients with primary central nervous system lymphoma (PCNSL) is less clear. Materials and methods: In a prospective trial, 42 FDG-PET examinations were performed in ten immunocompetent patients with newly diagnosed or recurrent PCNSL before and repeatedly during and after treatment. Brain and whole-body FDG-PET were compared to brain MRI and extracerebral CT, respectively. Results: Before treatment, 6 of the 10 patients had congruent findings in FDG-PET and MRI of the brain. Three patients had lesions on brain MRI not detected by FDG-PET. One patient had additional FDG-PET positive lesions inconspicious in MRI. Follow-up suggested FDG-PET to be false positive in these lesions. After treatment, brain PET was in agreement with MRI in 6 of 8 patients. In the remaining 2 patients there were persistent lesions in brain MRI whereas FDG-uptake was reduced to normal values. In the long-term follow-up of 5 patients (63-169 weeks), 3 patients retained normal in both PET and MRI. In 2 patients new focal pathologic FDG-uptake was detected 69 and 52 weeks after the end of treatment. In one of these patients, recurrence was confirmed by MRI not until 9 weeks after PET. Conclusion: Brain FDG-PET may contribute valuable information for the management of PCNSL, particularly in the assessment of treatment response. Integration of FDG-PET into prospective interventional trials is warranted to investigate prognostic and therapeutic implications. Keywords: PET-CT, PCNSL, CNS lymphoma, response assessment, imaging