A Schwann cell tumor is a growth that develops from Schwann cells, which form the protective lining around nerves in the peripheral nervous system. This system includes nerves outside of the brain and spinal cord. These tumors are generally slow-growing and, in most instances, are non-cancerous, or benign.
The Nature of Schwann Cell Tumors
Schwann cells are responsible for producing the myelin sheath, a fatty substance that insulates nerves and allows for the efficient transmission of electrical signals. When these cells proliferate abnormally, they form a tumor known as a schwannoma. These tumors are almost always encapsulated and grow on the surface of a nerve, often displacing the normal nerve fibers as they expand.
While the term “Schwann cell tumor” is broad, it most commonly refers to the benign schwannoma. In rare cases, these tumors can be cancerous, at which point they are classified as malignant peripheral nerve sheath tumors (MPNSTs). The vast majority of schwannomas, about 90%, occur sporadically without a known cause. A small percentage are linked to genetic disorders, most notably Neurofibromatosis type 2 (NF2), an inherited condition that disrupts the body’s ability to suppress tumor growth.
Common Symptoms and Locations
Symptoms of a Schwann cell tumor are tied to its size and location, arising from pressure the mass exerts on an adjacent nerve. Many small schwannomas may not produce any symptoms and are discovered incidentally. As a tumor enlarges, it can lead to a noticeable lump under the skin, localized pain, a burning or tingling sensation often described as “pins and needles,” and muscle weakness or numbness in the area controlled by the affected nerve.
These tumors can develop on almost any peripheral nerve in the body. Common locations include the nerves in the arms and legs, as well as those along the spinal column. When a schwannoma grows on a nerve root where it exits the spine, it can cause symptoms that mimic a herniated disk, such as radiating pain and weakness. A specific example is the vestibular schwannoma, also known as an acoustic neuroma. This tumor develops on the vestibular nerve, which connects the inner ear to the brain, and can lead to hearing loss, ringing in the ear (tinnitus), and balance problems.
Diagnostic Process
Diagnosing a Schwann cell tumor begins with a physical examination and a review of the patient’s medical history. A doctor may assess muscle strength, reflexes, and sensation in the affected area. Because symptoms can be similar to more common conditions, imaging tests are necessary for an accurate diagnosis.
Magnetic Resonance Imaging (MRI) is the preferred imaging method for identifying these tumors. An MRI provides detailed pictures of soft tissues, allowing doctors to visualize the tumor’s size, location, and its relationship to surrounding nerve structures. Computed Tomography (CT) scans may also be used. While imaging can strongly suggest a schwannoma, a biopsy is the definitive method to confirm the diagnosis and determine whether it is benign or malignant.
Treatment Approaches
The treatment for a Schwann cell tumor depends on its size, location, rate of growth, and whether it is causing symptoms. For small, slow-growing, and asymptomatic benign tumors, the initial approach is often observation, or “watchful waiting.” This involves monitoring the tumor with regular MRI scans to track any changes over time.
For tumors that are large, growing, or causing significant symptoms like pain or muscle weakness, surgical removal is the standard treatment. The goal of surgery is to remove the entire tumor while preserving the function of the affected nerve. Because schwannomas grow on the nerve sheath without deeply infiltrating the nerve fibers, complete removal is often possible without causing permanent nerve damage.
In situations where a tumor is located in a surgically difficult or high-risk area, such as near the brainstem, radiation therapy may be recommended. Stereotactic Radiosurgery is a highly focused form of radiation used to deliver a precise dose of radiation to the tumor. This non-invasive treatment aims to halt the tumor’s growth or shrink it, offering an alternative to open surgery.