Neurofibroma
A neurofibroma is a benign (non-cancerous) tumor that develops from the cells that form the protective sheath around peripheral nerves. These tumors are composed of Schwann cells, fibroblasts, and other supporting cells that normally surround nerve fibers. Neurofibromas can occur as isolated lesions in otherwise healthy individuals, but multiple neurofibromas are characteristic of neurofibromatosis type 1 (NF1), a genetic disorder. They can develop anywhere in the body where peripheral nerves are present, including skin, soft tissues, and along nerve pathways.
What is it?
Neurofibromas are soft, rubbery tumors that arise from the peripheral nerve sheath—the protective covering around nerves outside the brain and spinal cord. They develop from an overgrowth of cells that normally support nerve function, including Schwann cells (which produce myelin), fibroblasts (connective tissue cells), perineural cells, and mast cells. Unlike schwannomas (another type of nerve sheath tumor), neurofibromas are intimately intertwined with nerve fibers, making them more challenging to remove surgically without damaging the nerve.
There are three main types of neurofibromas: cutaneous neurofibromas, which are small bumps on or just under the skin; subcutaneous neurofibromas, which develop deeper in soft tissues along peripheral nerves; and plexiform neurofibromas, which are larger, more diffuse tumors involving multiple nerve branches, occurring almost exclusively in NF1 and carrying a small risk of malignant transformation. Neurofibromatosis type 1 is caused by mutations in the NF1 gene, which normally produces a protein (neurofibromin) that regulates cell growth. Loss of this regulation leads to tumor development. In individuals without NF1, sporadic neurofibromas may develop due to spontaneous genetic changes. Most neurofibromas are discovered during adolescence or young adulthood, and their number may increase over time, particularly in NF1 patients.
Important to Know
Many neurofibromas are asymptomatic and discovered incidentally during physical examination or imaging. When symptoms occur, they typically include visible or palpable soft lumps under the skin, tingling or numbness along the nerve distribution if the tumor compresses nerve fibers, pain or tenderness (especially with larger tumors or plexiform types), and cosmetic concerns when numerous or large cutaneous neurofibromas are present. Diagnosis is often made clinically based on appearance and characteristic soft, mobile texture. MRI is the preferred imaging modality for evaluating deeper neurofibromas, showing their relationship to nerves and surrounding structures. Biopsy may be performed if there is concern for malignant transformation, particularly with rapid growth, hardening, or new pain. Most neurofibromas are benign and slow-growing, requiring only observation. Treatment is indicated for symptomatic tumors causing pain, neurological deficits, or significant cosmetic concerns. Surgical excision is the primary treatment but can be challenging due to the tumor’s integration with nerve fibers, potentially causing nerve damage. Complete removal may not be possible for plexiform neurofibromas without sacrificing nerve function. For NF1-associated plexiform neurofibromas, the medication selumetinib has shown promise in shrinking tumors. Regular monitoring is important, particularly for plexiform neurofibromas, as approximately 8-13% may undergo malignant transformation into malignant peripheral nerve sheath tumors (MPNSTs). Warning signs include rapid growth, new or worsening pain, change in texture from soft to firm, and neurological symptoms.