A schwannoma is a tumor of the Schwann cells that serve as the protective covering of the nerves of the peripheral nervous system. The Schwann cells play a role in conducting electrical impulses along the nerve fibers. These tumors most often develop along the cranial nerve that controls hearing and are commonly referred to as vestibular schwannomas. These tumors can also develop along the nerves of the arm, lower back, and legs.
Definition & Facts
Most schwannomas occur by chance and are not inherited. Most patients with the condition only develop one tumor. Between 5 and 10 percent of patients will develop multiple schwannomas. This is usually the result of inherited conditions such as neurofibromatosis type II or schwannomatosis. Both of these conditions are autosomal dominant, which means that the individual only has to receive one copy of the mutated gene to develop schwannomas.
A person with schwannomatosis or neurofibromatosis type II has a 50 percent chance of passing the genetic mutation to their offspring. The majority of schwannomas are benign; however, there have been instances of malignant schwannomas.
Symptoms & Complaints
- Ringing in the ears
- Difficulty hearing on the side affected by the tumor
- Difficulties with balance
- Facial numbness,
- Dizziness or vertigo, and
If the peripheral nerves controlling motor function are affected, the patient may experience muscle weakness, numbness, or tingling along the affected nerve. Most patients with a schwannoma also experience a shock-like sensation, referred to as Tinel’s sign, when the area around the nerve is touched. Although rare, schwannomas can affect the nerves between the legs, which can cause bowel and bladder dysfunction.
Patients with neurofibromatosis type II also typically develop additional brain tumors and spinal cord tumors. Schwannomas normally grow slowly, so the symptoms develop gradually. Anyone experiencing a sudden onset of similar symptoms should seek immediate medical attention as they could indicate a stroke or other life-threatening condition.
It is believed that most cases of schwannoma are due to a mutation in a gene on chromosome 22 that produces the protein that controls the growth of Schwann cells. The mutation causes the cells to grow uncontrollably, which results in a tumor. In patients with neurofibromatosis type II or schwannomatosis, this mutation is inherited. In other cases, it is unclear what triggers the mutation.
Scientists are working to gain a better understanding of how this gene works. The hope is that this research will lead to the development of new treatments to control the production of Schwann cells. The only identifiable risk factor for schwannomas is a family history of neurofibromatosis type II and schwannomatosis.
Diagnosis & Tests
Since symptoms of a schwannoma can be subtle and often do not appear during the early stages of tumor growth, the condition can be difficult to diagnose. A doctor may suspect a schwannoma if the patient develops unilateral hearing loss or ringing in the ears along with dizziness or loss of balance. A physical examination, neurological evaluation, and balance testing can help rule out other potential causes of the symptoms. A complete hearing examination may also be performed. This may include
- An audiogram to measure hearing threshold at different frequencies,
- Electronystagmography can assess the function of the cranial nerves that control hearing, balance, and eye movements, and
- Auditory brainstem response tests that measure brain activity in response to sound.
Magnetic resonance imaging (MRI), which uses radio waves and a magnetic field to produce images of various body structures, can be used to identify the precise size and location of the tumor. Early detection of schwannomas is critical to prevent serious consequences, including permanent nerve damage. Treatment also becomes more difficult as the tumor grows and the risk of damaging nearby nerves increases.
Treatment and Therapy
The treatment of a schwannoma depends on its size, location, and the severity of the patient’s symptoms. If the tumor is small and asymptomatic, a doctor may recommend periodic observation and monitoring until the tumor starts to cause symptoms.
Most schwannomas do eventually require surgical excision. A variety of surgical approaches may be used depending on the location of the tumor. A schwannoma can recur if even a microscopic trace of the tumor is left behind. This is most likely to occur if the location of the tumor makes it difficult to access for complete excision. Recurrent schwannomas can be difficult to treat and may require a second surgery. Researchers are working on robotic technology to make it easier for surgeons to remove vestibular schwannomas successfully.
Radiation therapy may be used to reduce the size of the tumor or slow its growth. This is often the preferred treatment for patients who are elderly, in poor health, have vestibular schwannomas affecting both ears, or who have a schwannoma affecting their only functioning ear.
In patients with malignant schwannomas, chemotherapy may be used to shrink the size of the tumor; however, the treatment is unlikely to cure the condition. Malignant schwannomas tend to respond better to radiotherapy than chemotherapy. Since these tumors normally grow slowly, these treatments may be enough to control symptoms for many years.
Prevention & Prophylaxis
The outlook for patients with schwannomas varies based on individual factors. The size, location, and whether the tumor is operable are key factors that determine a patient’s prognosis. Treatments are successful in controlling symptoms in many patients; however, there is a chance for recurrence even with aggressive treatment.