The role of [18F]-fluorodeoxyglucose positron emission tomography in predicting plexiform neurofibroma progression

The role of FDG-PET for managing patients with plexiform neurofibromas (PN) is unclear. While many PN tumors exhibit periods of rapid growth, others grow slowly or unpredictably and may have periods of relative quiescence. The ability to predict which PN are likely to progress should facilitate a more timely initiation of medical treatments. Since conventional radiographic techniques have limited prognostic value, the use of a functional imaging modality to predict tumor progression is desirable. We hypothesized that PN tumors with high metabolic activity as demonstrated by FDG-PET are more likely to progress in the following year.

All patients were clinically stable, but were considered at high-risk for progression based on anatomical location of PN. FDG-PET scans were performed within two weeks of the baseline MRI study. Standardized uptake values (SUV) were calculated for all focally active index lesions and analyzed for correlation with changes in quantitative MRI over the ensuing year.

Fifteen of the 18 enrolled patients showed various degrees of FDG uptake as focal abnormalities, and these abnormalities corresponded to those noted on the MRI scans. Thirteen patients and 19 lesions were evaluable for PN volume change. The SUVmax ranged from 0.9 to 4 (median 1.5). There was a significant difference in the percent increase in PN volume in the following year for lesions that had an SUV > 2 compared to those with lower values (P = 0.016).

These findings support the hypothesis that FDG-PET imaging predicts PN growth rate, and, therefore, may assist clinician decision making with regard to treatment of PN and enrollment in clinical trials.