Nerve Sheath Tumor
A nerve sheath tumor is a growth that arises from the cells that make up the protective covering, or sheath, around a peripheral nerve or spinal nerve root. The two most common types are schwannomas and neurofibromas, both of which are usually benign and slow-growing. In the spine, nerve sheath tumors can appear along the nerve roots inside or just outside the spinal canal and may cause pain, numbness, tingling, or weakness if they compress nearby nerves or the spinal cord. Less commonly, nerve sheath tumors can be malignant and require more involved evaluation and treatment.
What is it?
Peripheral nerves and spinal nerve roots are surrounded by a protective layer of specialized cells, the most important being Schwann cells, which produce the myelin coating that helps nerves send signals efficiently. A nerve sheath tumor is a growth that develops from these supporting cells rather than from the nerve fibers themselves. Most nerve sheath tumors are benign and grow slowly, although they can produce symptoms by pressing on adjacent nerves, the spinal cord, or other nearby structures.
The most common nerve sheath tumors are schwannomas and neurofibromas. Schwannomas arise from Schwann cells and typically form a well-defined, encapsulated mass attached to one side of a nerve, often allowing the underlying nerve fibers to be preserved at surgery. Neurofibromas also arise from nerve sheath cells but tend to grow within and around the nerve fibers, which can make them more challenging to remove. Both are usually benign. In some cases, nerve sheath tumors are associated with inherited conditions such as neurofibromatosis type 1 (which predisposes to multiple neurofibromas and other features), neurofibromatosis type 2 (which is associated with schwannomas, particularly in the cranial and spinal nerves), or schwannomatosis. A small minority of nerve sheath tumors are malignant—called malignant peripheral nerve sheath tumors (MPNST)—and behave more aggressively, often arising in patients with neurofibromatosis type 1.
In the spine, nerve sheath tumors typically appear along the spinal nerve roots, either inside the dural sac (intradural-extramedullary) or extending through the neural foramen into the surrounding soft tissues, sometimes producing a characteristic “dumbbell” shape. Many small nerve sheath tumors cause no symptoms and are discovered incidentally on MRI. When symptoms occur, they depend on the location and size of the tumor and may include localized back or neck pain, radiating arm or leg pain that follows a specific nerve distribution, numbness or tingling, weakness, or muscle wasting. Larger tumors can compress the spinal cord and cause more widespread symptoms, including gait or balance difficulty, or, when located in the lower lumbar spine, features of cauda equina compression.
MRI of the spine with contrast is the preferred imaging test for evaluating a suspected nerve sheath tumor because it provides detailed views of the tumor’s size, shape, and relationship to surrounding nerves, the spinal cord, and bone. Nerve sheath tumors typically show characteristic features on MRI, although other lesions can sometimes look similar. CT may help evaluate associated bony changes, such as enlargement of a neural foramen or scalloping of a vertebra. Electrodiagnostic studies (EMG and nerve conduction) and, in some cases, biopsy may be used to clarify the diagnosis and guide treatment, particularly when malignancy is a concern.
Important to Know
Treatment depends on the type, location, size, and symptoms associated with the tumor. Small, asymptomatic benign nerve sheath tumors are often monitored with periodic MRI to assess for growth, particularly when they are stable in size and not causing symptoms. Surgical removal is the main treatment for benign tumors that are symptomatic, growing, or compressing the spinal cord or nerve roots, with the goal of relieving symptoms while preserving as much nerve function as possible. Many patients experience significant improvement after surgery for benign tumors. Malignant peripheral nerve sheath tumors are managed in specialized centers and typically involve a combination of surgery, radiation, and, in some cases, chemotherapy.
Patients with multiple nerve sheath tumors or other features suggestive of an inherited syndrome may benefit from genetic evaluation and coordinated care with specialists in genetics, neurology, neurosurgery, and oncology.
Red flag symptoms include rapidly worsening pain, progressive weakness or numbness, gait or balance difficulty, loss of bowel or bladder control, rapid growth of a known mass, or new neurological deficits, particularly in patients with neurofibromatosis. These warrant prompt medical evaluation, as they may indicate significant compression, transformation of a benign tumor to a malignant form, or another serious underlying condition.