Asymptomatic nonossifying fibroma-like lesions in neurofibromatosis type 1 patients

Aims: Neurofibromatosis type 1 (NF1) is genetic syndrome involving multiple tissues and organs including the skeleton. Because of prevalent tumours, NF1 patients often receive an MRI scan for the whole body. On MRI, skeletal findings resembling nonossifying fibroma (NOF) are frequently found. The clinical relevance of these lesions is unknown, so that diagnosis often leads to uncertainty for patients and physicians. The present study aims to explore the frequency of MRI-detectable NOF-like lesions and retrospectively evaluate associated clinical symptoms. Methods: A total of 333 NF1 patients who received at least one whole-body MRI were included. These MRI scans were assessed by a radiologist and an orthopaedic surgeon for NOF-like signals. For patients with NOF-like findings, medical records were re-evaluated to identify associated clinical symptoms. Results: A total of 127 NOF-like lesions were observed in 63 out of the 333 patients (19%). The most frequent region of the radiological lesions was the femur (57%), followed by the tibia (25%). Histology of two such lesions were NOF and fibrous dysplasia. For the majority (84%) of the patients with such NOF-like lesions, no associated symptoms were identified. Ten patients (16%) had mild transient symptoms in the proximity of their NOF-like lesions. However, extensive and follow-up examination excluded an association of these symptoms with the radiological lesions. Conclusion: NOF-like lesions are frequent on whole-body MRI scans of NF1 patients. However, there is no association with clinical symptoms. No specific treatment is indicated. These NOF-like lesions should be recognized as 'no-touch' lesions.