Can FDG PET/MRI be used to identify plexiform neurofibromas at high risk of malignant transformation to peripheral nerve sheath tumor?

Introduction: <InvalidTag charset="UTF-8" />To critically review the most recent literature pertaining to FDG PET/MRI’s utility in identifying neurofibromas with higher risk of progression to malignant peripheral nerve sheath tumors (MPNST) and evaluate the use of SUV max as a predictor for malignant transformation.

Methods: Several large scientific databases, including PubMed, Web of Science, and Google Scholar, were used to accumulate review articles and scientific communications relating to the clinical FDG PET/MRI practices in imaging neurofibromas. Next, review articles and scientific studies were compiled from the databases to accumulate a comprehensive body of literature. Specifically, articles will encompass today’s knowledge of neurofibromas as derived from FDG PET/MRI studies and reflect the most recent innovations in the molecular imaging of plexiform neurofibromas.

Results: FDG-PET MRI is considered ‘safer’ than FDG PET/CT due to the reduced radiation hazards in this population of patients whose underlying disease results from a knockout of tumor suppressor. FDG PET MRI is favorable in this sense compared to FDG PET CT, however, diagnostic sensitivity for PN with high risk of transformation to MPNST using FDG PET/MRI has not been explored extensively. Studies have found that FDG PET/MRI has been useful to help differentiate plexiform neurofibroma from both lymphoma and MPNST. These studies have suggested that the SUV max parameter to a be a reliable marker that can distinguish between pathologies. <w:sdt id="-106584202" sdttag="goog_rdk_0"></w:sdt><w:sdt id="-1338299735" sdttag="goog_rdk_1"></w:sdt>Furthermore, several studies have concluded to support the notion that an ideal SUV max threshold that can be a reliable predictor of progression of NF to MPSNT, with many corroborating studies suggesting a threshold of SUV max value greater than 3.5 be used to identify plexiform neurofibromas with high risk of malignant transformation.

Although SUV max has been proposed by some studies to be of value, this method may be suboptimal as arbitrarily creating a dichotomous classification of ‘benign’ and ‘malignant’ using SUV max may not be valid as FDG uptake and tumor aggressiveness can be placed on a continuous spectrum. Another reason why simply using a cutoff value of SUV MAX of 3.5 is that SUV measurements are affected by several physical, biological, and technical parameters, so if standardized protocols are not adopted by various institutions, SUV max values can result in vastly different interpretations and clinical decisions. The potential issues with using an SUV max value of >3.5 to predict malignant transformation of plexiform neurofibromas warrants further research into more accurate measurement values such as SUV peak or delta-SUV mean that may more properly assess prognosis of plexiform neurofibromas.

Review of literature suggests that Quantitative FDG PET/MRI parameters can augment, and even potentially serve as alternatives to, invasive biopsies in the future, however, further studies are needed to support these assertions. Additionally, other semi quantitative parameters that can serve as reliable predictors of increased risk of malignant transformation, aside from SUV max, should also be considered and require further investigation if clinicians wish to truly adopt FDG PET/MRI in the clinical management and care of neurofibroma patients.

Conclusions: Review of literature suggests that Quantitative FDG PET/MRI parameters could serve as alternatives to invasive biopsies, but further studies are needed to support these assertions. FDG PET MRI semi quantitative parameters have been suggested to help predict patient prognosis and risk of malignant transformation of PN to MPNST. Further evidence through well designed prospective studies is needed to lend support for further incorporation of FDG PET/MRI in neurofibroma cases. These studies should also look FDG PET/MRI parameters beyond SUV max as potential biomarkers for malignant transformation of plexiform neurofibromas.