Evaluation of intratumoural heterogeneity on ¹⁸F-FDG PET/CT for characterization of peripheral nerve sheath tumours in neurofibromatosis type 1.

Purpose: The aim of the study was to evaluate the potential usefulness of intratumoural tracer uptake heterogeneity on (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT as compared to a cut-off maximum standardized uptake value (SUVmax) for characterization of peripheral nerve sheath tumours (PNSTs) in neurofibromatosis type 1 (NF1).

Methods: Fifty patients suffering from NF1 were examined by (18)F-FDG PET/CT. Intralesional tracer uptake was analysed qualitatively and semi-quantitatively by measuring the mean and maximum SUV. Uptake heterogeneity was graded qualitatively using a three-point scale and semi-quantitatively by calculating an SUV-based heterogeneity index (HISUV). Cohen's κ was used to determine inter- and intra-rater agreement. Histopathological evaluation and clinical as well as radiological follow-up examinations served as the reference standards.

Results: A highly significant correlation between the degree of intratumoural uptake heterogeneity on (18)F-FDG PET and malignant transformation of PNSTs was observed (p < 0.0001). Semi-quantitative HISUV was significantly higher in malignant PNSTs (MPNSTs) than in benign tumours (p = 0.0002). Both intralesional heterogeneity and SUVmax could be used to identify malignant tumours with a sensitivity of 100 %. Cohen's κ was 0.86 for inter-rater agreement and 0.88 for intra-rater agreement on heterogeneity.

Conclusion: MPNSTs in patients with NF1 demonstrate considerable intratumoural uptake heterogeneity on (18)F-FDG PET/CT. Assessment of tumour heterogeneity is highly reproducible. Both tumour heterogeneity and a cut-off SUVmax may be used to sensitively identify malignant PNSTs, but the specificity is higher for the latter. A combination of both methods leads to a non-significant improvement in diagnostic performance.