[18F]FDG PET/CT in the diagnosis of malignant peripheral nerve sheath tumours in neurofibromatosis type-1.

The detection of malignant peripheral nerve sheath tumours (MPNSTs) in patients with neurofibromatosis 1 (NF1) remains a clinical challenge. The purpose of this study was to evaluate the use of [(18)F]2-fluoro-2-deoxy-D-glucose PET/CT (FDG PET/CT with early and delayed imaging) in patients with symptomatic neurofibromas, to revalidate current cut-off values for identification of malignant change within neurofibromas and to examine the relationship between SUV and tumour grade. Patients with symptomatic neurofibromas underwent FDG PET/CT imaging at 90 and 240 min. Semiquantitative analysis using maximum standardized uptake value (SUVmax) was performed and correlated with histology. In 69 patients, 85 lesions were identified for analysis, including 10 atypical neurofibromas and 21 MPNSTs. Sensitivity of FDG PET/CT in diagnosing NF1-associated MPNST was 0.97 (95% CI 0.81-0.99) and the specificity was 0.87 (CI 0.74-0.95). There was a significant difference in SUVmax between early and delayed imaging and in SUVmax between tumours identified as benign and malignant on PET/CT. There was also a significant difference in SUVmax between tumour grades. FDG PET/CT is a highly sensitive and specific imaging modality for the diagnosis of MPNST in NF1 patients. We recommend performing early (90 min) and delayed imaging at 4 h for accurate lesion characterization and using a cut-off SUVmax of 3.5 on delayed imaging to achieve maximal sensitivity.