Ossification of neurofibroma in neurofibromatosis type 1, a case report of a rare presentation

Introduction: Although musculoskeletal involvement of Neurofibromatosis type 1 (NF1) has been well documented, bone formation, or ossification, within neurofibroma, has been scarcely documented in literature. Here, we report a rare case of ossified neurofibroma in a patient with long history of NF1. Presentation of case: 73-Year-old female with childhood-onset NF1 and surgical history of resection for multiple neurofibromas, presented with right ptosis and eyebrow ptosis. A growing tumor on the right eyebrow was surgically resected. Microscopically, the dermal tumor consists of bland spindle cells with thin, wavy nuclei, without atypia, showing S100 immunoreactivity, consistent with neurofibroma. Multiple metaplastic bone formation composed of mature bone trabeculae surrounding adipose tissue were apparent. Discussion: Up to date, ossification of neurofibroma has been scarcely reported in literature. The etiology is unclear but might involve the response to chronic stress and tissue damage over the years, and/or might indicate the potential differentiation plasticity of mesenchymal stem cell-like population. Conclusion: The unusual presentation of ossification provides insights on the pathogenesis and differentiation plasticity of neurofibroma.