A vestibular schwannoma is a noncancerous tumor on the main nerve leading from the inner ear to the brain. This vestibulocochlear nerve has branches that influence your balance and hearing. When a tumor, also called an acoustic neuroma, forms on this nerve, it can lead to symptoms like one-sided hearing loss, tinnitus, and dizziness. Stereotactic radiosurgery is a non-invasive treatment that uses highly focused radiation beams to manage the tumor and is a primary option for many patients.
The Radiosurgery Procedure Explained
Stereotactic radiosurgery (SRS) is not a traditional surgical operation and involves no incisions. The process begins with detailed planning, where imaging tests such as Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scans are used to create a precise, three-dimensional map of the tumor’s exact size and location. This mapping allows clinicians to target the tumor with a high degree of accuracy while protecting surrounding brain structures.
To ensure the radiation is delivered exactly as planned, the patient’s head must be kept perfectly still during treatment. This is accomplished through immobilization. One method involves a lightweight stereotactic head frame, which is secured to the head under local anesthetic. Another technique uses a non-invasive, custom-fitted mesh mask that molds to the patient’s face and is secured to the treatment table.
During the treatment itself, which is a single outpatient session, the patient is awake and the procedure is painless. Specialized equipment delivers many small, focused beams of radiation to the tumor from hundreds of different angles. While each individual beam is too weak to harm the healthy tissue it passes through, the point where all beams converge receives a high, cumulative dose of radiation. This energy damages the DNA of the tumor cells, preventing them from dividing and growing.
Several technologies can be used to perform radiosurgery, including Gamma Knife, CyberKnife, and systems based on linear accelerators (LINAC). Gamma Knife uses about 200 small beams of gamma rays simultaneously, while LINAC-based systems and CyberKnife use a single, computer-guided beam that moves around the patient to deliver radiation from many positions. Although the delivery mechanisms differ, all these technologies operate on the same principle of directing a precise radiation dose to the tumor and minimizing exposure to adjacent healthy tissues.
Determining Candidacy for Treatment
Deciding if a patient is a suitable candidate for radiosurgery involves evaluating several factors. A primary consideration is the size and location of the vestibular schwannoma. Radiosurgery is most effective for tumors that are small to medium in size, typically less than 2.5 to 3 centimeters in diameter. For larger tumors causing significant pressure on the brainstem, microsurgery might be recommended first.
Patient-specific factors, including age and overall health, also play a role in the decision. Radiosurgery is often a preferred treatment for older individuals or for patients who have other medical conditions that could make open surgery riskier. Because it is a non-invasive outpatient procedure, it avoids potential complications associated with general anesthesia and a prolonged hospital stay.
The level of hearing a person has in the affected ear is another element in determining the best course of action. Treatment decisions are often made with the goal of preserving whatever hearing function remains. If a patient has good, serviceable hearing, the team will weigh the potential for hearing preservation with radiosurgery against other options.
Ultimately, the choice of treatment is a shared decision between the patient and their medical team. After an explanation of all available options—which may include observation, microsurgery, or radiosurgery—the patient’s preferences are taken into account. This process ensures the chosen path aligns with the patient’s health, lifestyle, and personal goals.
Goals and Long-Term Outcomes
The primary objective of radiosurgery is not to remove the tumor, but to control its growth by stopping the tumor cells from multiplying. Following treatment, the tumor does not disappear immediately. It may shrink over a period of 18 months to two years or, more commonly, remain stable in size, preventing further growth. Studies show that radiosurgery successfully stops or shrinks the tumor in over 96% of cases.
A focus of long-term outcomes is the preservation of neurological function, particularly hearing. While tumor control is the primary goal, a secondary aim is to preserve existing hearing. The success of hearing preservation can vary, but studies found that serviceable hearing was maintained in nearly 60% of cases. Factors that favor better hearing outcomes include younger age, better hearing status before treatment, and smaller tumor volume. Some degree of hearing loss can still occur, sometimes developing gradually years after the procedure.
Preserving the function of other nearby cranial nerves is an advantage of radiosurgery. The facial nerve, which controls facial expression, and the trigeminal nerve, responsible for facial sensation, are located close to the tumor. The precision of radiosurgery minimizes radiation exposure to these adjacent nerves, so the risk of permanent facial weakness or numbness is very low, with rates of facial nerve deficits reported to be around 1.3% and trigeminal nerve issues around 3.2%.
For a small percentage of patients, the tumor may show a temporary increase in volume in the months following treatment before it stabilizes or shrinks. This transient swelling is a known response to the radiation and does not signify treatment failure. Long-term follow-up confirms that even with this initial response, the vast majority of tumors are successfully controlled.
Recovery and Potential Side Effects
The recovery period following radiosurgery for a vestibular schwannoma is brief. Since the procedure is non-invasive and performed on an outpatient basis, most individuals can go home the same day. Patients are often able to return to their normal activities within a day or two. This contrasts with the longer recovery period required after traditional open surgery.
Immediately after the procedure, some patients may experience mild and temporary side effects, including fatigue, headaches, or nausea. Because the tumor is located on the balance nerve, some individuals may experience new or worsened dizziness or imbalance. These vestibular symptoms are common, but for most, these symptoms resolve over time.
While the risk of serious complications is low, some side effects can develop months or years after treatment. Delayed hearing loss is a possibility and tends to progress slowly over several years. Hydrocephalus, a buildup of fluid in the brain, is an infrequent complication that can be caused by the tumor itself or a reaction to the treatment that blocks fluid circulation.
To ensure the treatment has been successful, long-term monitoring is a standard part of post-procedure care. Patients will undergo periodic MRI scans to track the size of the tumor and confirm that it is not growing. This regular follow-up allows the medical team to manage any late-emerging side effects.