Neurofibromas are nerve sheath tumors, or tumors of the layer of insulation that surrounds nerve fibers. Neurofibromas arise from Schwann cells, which produce the insulating sheath for all nerves outside the brain and spinal cord.
At The Spine Hospital at The Neurological Institute of New York, we specialize in neurofibromas of the spine. Note that these tumors do not arise in the spinal cord, which is part of the central nervous system. These tumors arise instead on the nerves that leave the spinal cord to branch out to the rest of the body, known as nerve roots or peripheral nerves.
Nerve roots leave the spine through small openings in the spinal canal called the foramen. The neurofibromas that grow along nerve roots are therefore often dumbbell shaped. That is, one part of the mass is inside the spinal canal and one part is outside; they are connected by a narrow section that passes through the foramen.
The vast majority of neurofibromas–90 to 95%–are benign (noncancerous) tumors. But even benign neurofibromas can present a problem when they compress important structures like spinal nerves or the spinal cord.
Symptoms result when a growing tumor encroaches on the surrounding structures. Common symptoms that occur when a neurofibroma compresses the spinal cord or nerve roots include:
- Changes in sensation (pain, numbness, tingling)
- Changes in movement (clumsiness in the hands, trouble walking)
- Changes in bowel or bladder function (a sense of urgency when urinating, bowel or bladder incontinence)
An abnormal curvature of the spine, called a scoliosis, can also result if the tumor creates muscular imbalance or erodes bones of the spine.
Causes and Risk Factors
Neurofibromas most often occur in people who have a genetic condition called neurofibromatosis. Two forms of this condition, NF1 and NF2, cause neurofibromas throughout the body.
Neurofibromatosis I (NF1) is less likely to cause spinal tumors. Neurofibromatosis II (NF2) is likely to cause multiple neurofibromas, meningiomas of the brain or spinal cord, and ependymomas of the spinal cord.
Neurofibromas can also occur in people without neurofibromatosis. These are called sporadic cases. People with sporadic neurofibromas are likely to have only a single tumor–not multiple tumors, as with NF2.
Tests and Diagnosis
Neurofibromas can be identified on MR (magnetic resonance) and CT (computed tomography) scans. MR scans use magnets, radio waves, and computer technology to produce images of organs and tissues like the brain and spinal cord. CT scans use a combination of X-rays and computer technology to produce detailed images of bones and soft tissues.
On these scans, neurofibromas resemble schwannomas, another type of nerve tumor. These tumor types may be impossible to distinguish on imaging and often require tissue biopsy for pathologic evaluation in the laboratory. Neurofibromas are the more difficult type of tumor to remove because they are more intimately involved with the nerve fibers. However, with meticulous surgical technique, most can be removed safely.
The treatment of spinal neurofibromas depends on the size, location, and symptoms of the tumor. Small tumors producing no pressure on nearby structures in patients with no symptoms can often be observed over time with yearly MR scans.
For larger or symptomatic tumors, or tumors showing growth over time, surgical removal is usually recommended. In most patients, complete removal of these tumors can be safely achieved using a surgical microscope, an array of microsurgical techniques, and with the experience of doctors like those at The Spine Hospital at the Neurological Institute. In many cases, patients experience an improvement in neurological function (see video). In some patients with large dumbbell tumors, spinal stabilization and fusion may be performed following complete tumor removal (see video).