Comprehensive anatomical and functional imaging in patients with type I neurofibromatosis using simultaneous FDG-PET/MRI

Purpose To demonstrate the clinical use of FDG-PET/MRI for monitoring enlargement and metabolism of plexiform neurofibromas (PNF) in patients with neurofibromatosis type 1 (NF1), in whom the development of a malignant peripheral nerve sheath tumor (MPNST) is often a life limiting event. Methods NF1 patients who underwent a simultaneous FDG-PET/MRI examination in our institution from September 2012 to February 2018 were included. Indication was suspicion of malignant transformation of a PNF to MPNST. A maximum of six peripheral nerve lesions per patient were defined as targets. Standardized uptake values (SUV) and apparent diffusion coefficients (ADC) were measured. The presence of target sign and contrast-medium enhancement was visually recorded. Growth rates were estimated comparing prior or follow-up examinations and correlated with FDG uptake and ADC values. The presence of CNS lesions in cerebral T2 weighted images was recorded. Results In 28 NF1 patients a total number of 83 peripheral nerve tumors, 75 benign PNFs and eight MPNSTs, were selected as target lesions. The SUVs of MPNSTs were significantly higher than the SUVs of PNF (3.84 ± 3.98 [SUV mean MPNSTs] vs. 1.85 ± 1.03 [SUV mean PNF], P