A neurofibroma is a benign tumor that grows on or around nerves. It develops from a mix of cell types found in the nerve’s protective sheath, including the cells that insulate nerve fibers, connective tissue cells, and immune cells called mast cells. Neurofibromas can appear anywhere in the body where nerves exist, from just beneath the skin to deep inside the chest or abdomen.
Most neurofibromas cause mild symptoms or none at all. They become a concern when they press on nerves, grow large enough to affect appearance, or carry a risk of turning cancerous. Understanding the type of neurofibroma you’re dealing with is key, because treatment options and long-term outlook vary significantly depending on where the tumor is and how it behaves.
What Causes a Neurofibroma
Neurofibromas form because of a mutation in a gene called NF1, located on chromosome 17. This gene provides the blueprint for a protein called neurofibromin, which acts as a built-in brake on cell growth. When the gene is mutated, that brake fails, and cells in the nerve sheath begin multiplying in an uncontrolled way. The result is a slow-growing mass made up of several cell types that normally surround and support nerve fibers.
Neurofibromas can be either sporadic or syndromic. Sporadic neurofibromas occur as isolated, one-off tumors in people who are otherwise healthy. In these cases, the NF1 mutation exists only in the tumor cells themselves. Syndromic neurofibromas are linked to a genetic condition called neurofibromatosis type 1 (NF1), where the mutation is inherited and present in every cell of the body. People with NF1 typically develop multiple neurofibromas over their lifetime, sometimes dozens or more.
Three Main Types
Localized (Cutaneous) Neurofibroma
This is the most common type. It appears as a soft, painless bump on or just under the skin, usually skin-colored, pink, or tan. Localized neurofibromas most often show up in adults between the ages of 20 and 40. They’re typically small, grow slowly, and rarely cause problems beyond cosmetic concerns. A person without NF1 might develop a single one and never get another.
Diffuse Neurofibroma
Rather than forming a distinct lump, diffuse neurofibromas spread through a broader area of tissue, creating a thickened, plaque-like growth. They tend to occur in the skin and the fatty layer beneath it, and they’re less common than localized types. Because they blend into surrounding tissue, they can be harder to define on physical exam and may require imaging to fully characterize.
Plexiform Neurofibroma
Plexiform neurofibromas involve multiple nerve branches at once, growing along the nerve in thick, irregular bundles that can become quite large. They’re strongly associated with neurofibromatosis type 1 and are considered a hallmark of that condition. Unlike localized neurofibromas, plexiform tumors infiltrate surrounding normal tissue, making them difficult or impossible to remove completely. They also carry the highest risk of complications, including pain, disfigurement, and malignant transformation.
Symptoms and What They Feel Like
Many neurofibromas produce no symptoms at all and are discovered incidentally during a physical exam or imaging scan done for another reason. When symptoms do occur, they depend largely on the tumor’s size and location.
Skin-level neurofibromas usually present as a visible or palpable bump. Some people notice mild tenderness if the area is pressed, and occasionally the overlying skin can bleed if irritated. Deeper neurofibromas or those growing within a nerve can cause tingling, numbness, weakness, or pain in the area the nerve supplies. A plexiform neurofibroma on the face can alter appearance as it enlarges, and one growing near the spine can compress the spinal cord or nerve roots, leading to more significant neurological symptoms.
Pain is more common with plexiform neurofibromas than with smaller cutaneous ones. Rapid growth, a sudden increase in pain, or new neurological deficits in a previously stable tumor are warning signs that should be evaluated promptly, as they can indicate malignant change.
How Neurofibromas Are Diagnosed
Diagnosis typically starts with a physical examination and a detailed personal and family history, particularly to assess whether NF1 might be present. Imaging is the next step for tumors that can’t be fully evaluated by touch alone.
MRI is the primary tool for characterizing neurofibromas, especially plexiform types. On MRI, neurofibromas often display what radiologists call a “target sign”: a central dark area surrounded by a bright rim on certain scan sequences. This pattern is considered a hallmark of plexiform neurofibromas and reflects the internal structure of the involved nerve bundles. The tumors also tend to appear lobulated and show high signal intensity on fluid-sensitive sequences. Ultrasound can reveal a similar target pattern and is sometimes used as a first-line imaging tool for superficial tumors.
When imaging alone isn’t enough to confirm the diagnosis or rule out malignancy, a biopsy is performed. Under the microscope, neurofibromas have a distinctive appearance: wavy, spindle-shaped cell nuclei interspersed with collagen fibers, often set in a loose, gel-like background. Pathologists use specific staining techniques to confirm the cell types present and distinguish neurofibromas from other nerve sheath tumors like schwannomas.
Risk of Becoming Cancerous
Most neurofibromas remain benign throughout a person’s life. The concern lies primarily with plexiform neurofibromas in people who have NF1. These tumors are considered precancerous lesions that can progress into a malignant peripheral nerve sheath tumor (MPNST), an aggressive form of cancer.
The estimated lifetime risk of this malignant transformation for people with NF1 is about 4.6%. While that number may sound low, MPNST is a serious cancer with limited treatment options, so monitoring is critical. People with cutaneous neurofibromas and NF1 also face a roughly threefold increased risk of developing MPNST compared to the general population. Signs that raise suspicion for malignant change include rapid tumor growth, escalating pain, and new neurological symptoms. Surgical biopsy is often the only way to confirm or rule out malignancy in a suspicious lesion.
Treatment Options
Surgery
Surgical removal is the standard treatment for neurofibromas that cause symptoms, are cosmetically bothersome, or show concerning features. For localized neurofibromas, surgery is usually straightforward and curative. The tumor is well-defined, and a skilled surgeon can typically remove it while preserving nerve function.
Plexiform neurofibromas are a different story. Because they infiltrate surrounding tissue and involve multiple nerve branches and blood vessels, complete removal is often impossible. Surgeons aim to reduce the tumor’s size and relieve symptoms, but even after resection, 40 to 50% of plexiform neurofibromas regrow. Cervical (neck) lesions are particularly challenging, as they span multiple spinal levels in about 85% of cases, making only partial removal feasible. The decision to operate on a plexiform neurofibroma depends on its location, growth rate, whether it’s compressing vital structures, and the patient’s overall health.
When a plexiform neurofibroma can’t be safely removed but malignant transformation is suspected, a biopsy remains essential for guiding the next steps in care.
Medication for Inoperable Tumors
For plexiform neurofibromas that cause symptoms but can’t be surgically removed, a targeted drug called selumetinib (brand name Koselugo) is now FDA-approved. It works by blocking a specific signaling pathway that drives tumor cell growth, essentially restoring part of the braking system that the NF1 mutation disables. Selumetinib is taken by mouth twice daily and has been shown to shrink inoperable plexiform neurofibromas in both children and adults with NF1. Its approval marked a significant shift in how these tumors are managed, offering a non-surgical option for the first time.
Living With a Neurofibroma
For people with a single, small neurofibroma and no family history of NF1, the outlook is excellent. The tumor can often be removed if desired, and recurrence after complete removal is uncommon. No special monitoring is typically needed afterward.
For people with NF1 and multiple neurofibromas, management is more involved. Regular imaging, usually with MRI, helps track tumor size and detect any changes that might signal malignant transformation. The frequency of monitoring depends on the number, size, and behavior of the tumors. Many people with NF1 live full lives with careful surveillance and timely intervention when tumors become problematic. Support from a multidisciplinary team that includes neurologists, surgeons, geneticists, and oncologists provides the most comprehensive care for complex cases.