Atypical plexiform neurofibroma in NF1 with high standardised uptake value (SUV) in positron-emission tomography (PET) expressing podoplanin.

A 19-year-old female with established neurofibromatosis type 1 (NF1) diagnosis and history of malignant peripheral nerve sheath tumour (MPNST) of the lower extremities showed a tumour of her right upper extremity with a maximum standardised uptake value (SUV) of 5.7 on positron emission/computerised tomography (PET/CT) scan. The extirpated tumour proved to be an atypical plexiform neurofibroma. Immunohistochemical investigations revealed a strong positive reaction of tumour cells for S-100 protein. Epithelial membrane antigen (EMA)-positive perineural cells were demonstrated at the border of the tumour. Scattered nerve fibres were labelled with neurofilament antibodies within the tumour. The maximum Ki-67 labelling index reached 9%. Slight to moderate podoplanin expression of the tumour cells was noted in areas of fibrillary growth. Podoplanin expression has been proposed as a differentiation marker for schwannomas and neurofibromas. This atypical neurofibroma showed a high SUV on PET that is indicative for MPNST. It appears likely that subtypes of Schwann cells express podoplanin. This marker may be useful in distinguishing different Schwann cell populations in neurofibromas.