Discrimination of benign, atypical, and malignant peripheral nerve sheath tumours in neurofibromatosis type 1 – intraindividual comparison of positron emission computed tomography and diffusion-weighted magnetic resonance imaging

Abstract Background To intraindividually compare the diagnostic performance of positron emission computed tomography (F-18-FDG-PET/CT) and diffusion-weighted magnetic resonance imaging (DW-MRI) in a non-inferiority design for the discrimination of peripheral nerve sheath tumours as benign (BPNST), atypical (ANF), or malignant (MPNST) in patients with neurofibromatosis type 1 (NF1). Results In this prospective single-centre study, thirty-four NF1 patients (18 male; 30 ± 11 years) underwent F-18-FDG-PET/CT and multi-b-value DW-MRI (11 b-values 0 – 800 s/mm²) at 3T. Sixty-six lesions corresponding to 39 BPNST, 11 ANF, and 16 MPNST were evaluated. Two radiologists independently assessed the maximum standardized uptake value (SUVmax) and mean and minimum apparent diffusion coefficient (ADCmean/min) as well as the ADC in areas of lowest signal intensity in each lesion (ADCdark). The AUCs of DW-MRI and F-18-FDG-PET/CT were compared to determine whether the ADC is non-inferior to SUVmax (non-inferiority margin equal to -10%). Follow-up of ≥ 24 months (BPNST) or histopathological evaluation (MPNST + ANF) served as diagnostic reference standard. Both SUVmax and ADC parameters demonstrated good diagnostic accuracy (AUCSUVmax 94.0%; AUCADCmean/min/dark 91.6% / 90.1% / 92.5%). However, non-inferiority could not be demonstrated for any of the three ADC parameters (lower limits of the confidence intervals of the difference between the AUC of ADCmean/min/dark and SUVmax -12.9% / -14.5% / -11.6%). Inter-rater reliability was excellent for both imaging techniques (Krippendorff’s alpha all > 0.94). Conclusions Both PET/CT-derived SUVmax and MRI-derived ADC allow sensitive and non-invasive differentiation of benign and (pre)-malignant peripheral nerve sheath tumours. Nevertheless, DW-MRI cannot be considered as non-inferior to F-18-FDG-PET/CT in this prospective single-centre study.