Does adding FDG-PET to MRI improve the differentiation between primary cerebral lymphoma and glioblastoma? Observer performance study.

Objective: It is sometimes difficult to distinguish between primary central nervous system lymphomas (PCNSL) and glioblastoma multiforme (GBM). The aim of this study was to investigate whether the addition of (18)F-2-fluoro-2-deoxy-D: -glucose positron emission tomography ([(18)F]FDG-PET) and apparent diffusion coefficients (ADC) to conventional MRI improves diagnostic accuracy for distinguishing between PCNSL and GBM with similar MRI findings.

Methods: We used conventional- and diffusion-weighted MRI and FDG-PET scans of 21 patients with histologically confirmed brain tumors exhibiting similar MRI findings (PCNSL, n = 14, GBM, n = 7) in our observer performance study that consisted of 3 interpretation sessions. ADC and maximum standard uptake values (SUV(max)) of the tumors were calculated. Three radiologists first interpreted conventional MRI (1st session), then they read images to which the ADC value had been added (2nd session), and finally they interpreted images supplemented with SUV(max) (3rd session). Observer performance was evaluated using κ statistic and receiver operating characteristics analyses.

Results: The addition of ADC values to conventional MRI failed to improve the differentiation between PCNSL and GBM. The addition of SUV(max) at the third session improved the diagnostic accuracy of all 3 readers and resulted in higher interobserver agreement; mean accuracy was 95% (range 93-100%). In one observer the accuracy of tumor differentiation was significantly improved at the third compared to the second session (p = 0.017).

Conclusions: In a selected group of PCNSL and GBM with similar MRI findings, the addition of quantitative FDG-PET to MRI may improve their differentiation. ADC measurement did not allow further discrimination.