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Objective: The aim of this study is to evaluate neurofibromatosis type 1 (NF1) patients with whole-body MRI (WBMRI) to investigate the frequency of plexiform neurofibromas (pNFs), diffuse neurofibromas (dNFs), and malignant peripheral nerve sheath tumors (MPNSTs)., Materials and Methods: In this retrospective cross-sectional study, between the years 2015 and 2023, 83 consecutive patients with known NF1 underwent a total of 110 WBMRI screenings for MPNST using a standardized institutional protocol. The lesions are categorized as discrete lesions, pNFs, dNFs, and MPNSTs. Histopathology served as the reference standard for all MPNSTs., Results: Among the 83 patients analyzed, 53 (64%) were women and 30 were men (36%) of ages 36.94±14.43 years (range, 15-66 years). Of the 83 patients, 33 have a positive family history of NF1 and positive genetic studies. Seven of 83 (8%) have only dNF, 20/83 (24%) have pNF, 28/83 (34%) have both dNF and pNF, and 28/83 (34%) have neither. Of the 83 patients, eight (9.6%) were diagnosed with nine total MPNSTs. Age range for patients with MPNSTs at time of diagnosis was 22-51, with an average age of 33.4 years. Only one MPNST (11%) developed from underlying pNF 4 years after WBMRI along the right bronchial tree. Three of eight (37.5%) patients with MPNST died within 5 years of pathologic diagnosis., Conclusion: This study suggests the absence of a predisposition for development of MPNST from pNFs and dNFs in the setting of NF1. As such, these lesions may not need special surveillance compared to discrete peripheral nerve sheath tumors., (© 2023. The Author(s), under exclusive licence to International Skeletal Society (ISS).)

Clinical Problem: Neurofibromatosis type 1 (NF1) and tuberous sclerosis (TS) are among the most common genetic diseases. Bone and soft tissue manifestations are common disease manifestations., Standard Radiological Procedure and Evaluation: The standard radiological procedure is magnetic resonance imaging (MRI). All macroscopic disease manifestations can be diagnosed radiologically and observed during the course. Specific complications such as plexiform neurofibromas and malignant peripheral nerve sheath tumors (MPNST) in NF1 are readily visible on MRI. Differentiation of plexiform neurofibromas and MPNST is uncertain and requires follow-up., Recommendation for Practice: MRI is the most important procedure for the investigation of soft tissue and bone manifestations of NF1 and TS., (© 2021. Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Plexiform neurofibromas are an uncommon variant of neurofibromas that are described as being essentially pathognomonic of neurofibromatosis type 1 (NF1). Plexiform neurofibromas in the absence of NF1 are extremely rare. We present the case of a 38-year-old woman with a large multilobulated lumbosacral mass extending into the pelvis and proximal thigh. Histopathology of a CT-guided biopsy of the mass revealed it to be a neurofibroma. The imaging findings were consistent with a plexiform subtype. Further imaging and clinical workup showed that the patient had no other identifiable neurofibromas and did not meet criteria for the diagnosis of NF1.

Ossifying subperiosteal haematoma is an exceedingly rare manifestation of Neurofibromatosis type 1 (NF-1). We report an interesting case of plexiform neurofibroma causing a rapidly growing tibial mass as a result of subperiosteal haemorrhage, in an 11-year-old girl with previously undiagnosed NF-1. This reflects a precursor of the more mature periosteal ossification seen in cases traditionally termed "subperiosteal cysts". A previously well young girl was referred by her general practitioner with an increasingly large, mildly tender, soft lump on the anterior aspect of her right tibia. Plain radiographs demonstrated soft tissue thickening overlying the anterior tibia, without appreciable periosteal ossification. Magnetic resonance imaging (MRI) illustrated a single central fluid-fluid level and periosteal elevation with saucerisation of the anterior tibial cortex and mild surrounding oedema. Histopathology revealed a large plexiform neurofibroma. Interestingly, this was associated with haemorrhagic change and a peripheral rim of florid reactive new bone formation. This unusual presentation was discussed at a multidisciplinary bone and soft tissue tumour meeting, where in combination with the clinical history of café au lait spots and positive family history, a consensus diagnosis of NF-1 was made. To date, there have only been limited case reports of this rare pathological process. In summary, this case report accounts an acute presentation of this rare osseous manifestation of NF-1, being the first to clearly demonstrate a timeline of subperiosteal haematoma with subsequent subperiosteal bone proliferation. The clinical reasoning and radiological features for such a presentation are also described.