Vestibular schwannoma, also known as acoustic neuroma, is a benign growth on the eighth cranial nerve. This nerve transmits sound and balance information from the inner ear to the brain. Though not cancerous, these slow-growing tumors can cause issues by pressing on nerves and brain structures. Gamma Knife radiosurgery offers a non-invasive, focused radiation treatment to manage these tumors without traditional surgery.
Understanding Vestibular Schwannoma
A vestibular schwannoma is a non-cancerous, slow-growing tumor developing from Schwann cells, which insulate nerves. These tumors arise on the vestibulocochlear nerve (eighth cranial nerve), responsible for hearing and balance. As the tumor enlarges, it can exert pressure on this nerve and adjacent brain structures.
Common symptoms include progressive hearing loss, often in one ear, and tinnitus (a ringing or buzzing sensation). Patients may also experience balance issues like dizziness or unsteadiness, and a feeling of fullness in the ear. While the exact cause for most sporadic cases is unknown, some instances link to neurofibromatosis type 2 (NF2), a genetic disorder.
How Gamma Knife Radiosurgery Works
Gamma Knife radiosurgery is a specialized radiation therapy that precisely targets abnormal growths within the brain. It uses highly focused gamma radiation beams to deliver a concentrated dose to a specific target area, without a surgical blade or incisions.
The system converges multiple individual radiation beams at a single point: the tumor. Each beam is low intensity, minimizing damage to healthy brain tissue it passes through. Only at the precise focal point, where all beams intersect, does the radiation dose become high enough to affect tumor cells.
This precision is achieved through advanced imaging (MRI or CT scans) that maps the target’s exact location and shape. The focused radiation damages tumor cell DNA, preventing growth and reproduction. Over time, this cellular damage leads to gradual shrinkage or cessation of growth. Gamma Knife technology delivers an intense radiation dose while sparing surrounding delicate brain structures.
The Gamma Knife Procedure for Vestibular Schwannoma
The Gamma Knife procedure for a vestibular schwannoma begins with placing a stereotactic head frame. This frame temporarily attaches to the patient’s skull with pins, under local anesthesia, to keep the head still during imaging and treatment. The frame also guides precise radiation targeting.
Once the head frame is in place, high-resolution MRI scans pinpoint the tumor’s exact location, size, and shape. These images provide the medical team with detailed information for treatment planning. A neurosurgeon, radiation oncologist, and medical physicist collaborate to create a customized plan.
This planning determines the precise angles and intensities of gamma radiation beams to ensure the tumor receives the prescribed dose while minimizing exposure to surrounding healthy brain tissue and nerves. The plan defines how multiple radiation “shots,” or small spheres of radiation dose, will be strategically delivered to cover the entire tumor volume.
During treatment, the patient lies on a movable couch, and the head frame secures to the Gamma Knife unit. The machine delivers the precisely planned radiation beams. The patient does not feel the radiation during the session, which can last from several minutes to a few hours depending on tumor characteristics. Most Gamma Knife procedures for vestibular schwannoma are performed in a single outpatient session, allowing patients to return home the same day after the head frame is removed.
Effectiveness and Patient Experience
Gamma Knife radiosurgery aims to halt vestibular schwannoma growth, with many tumors showing subsequent shrinkage. Studies indicate high tumor control rates, ranging from 90% to 99%, meaning the tumor stops growing or decreases in size. This gradual response occurs as irradiated tumor cells are damaged and eventually reabsorbed by the body.
A key goal is to preserve existing neurological functions, particularly hearing. While hearing preservation rates vary, some studies report serviceable hearing preservation in 50% to 78.2% of patients, especially with lower radiation doses. Functional preservation also extends to other cranial nerves, with facial nerve preservation rates exceeding 96%.
Patients may experience short-term side effects like mild headaches, nausea, or fatigue, which are manageable with medication. Acute effects like new or worsened vertigo and gait disturbance have been reported in a minority of patients, resolving within six months. Delayed or rarer side effects, including facial numbness or increased balance issues, can occur but are less common compared to traditional surgical approaches. The full effects of Gamma Knife treatment become apparent gradually over several months to years.
Life After Gamma Knife
Following Gamma Knife radiosurgery, regular follow-up appointments and imaging scans are part of patient care. MRI scans are performed at regular intervals to monitor the tumor’s response. Initially, these scans might be scheduled every 6 to 12 months.
While initial swelling or a temporary increase in tumor size (pseudoprogression) can occur in the first one to two years, this is a normal part of healing and resolves. The long-term goal of follow-up imaging is to confirm sustained tumor control, with scan frequency potentially decreasing if the tumor remains stable.
Most patients can resume normal daily activities quickly after Gamma Knife radiosurgery due to its non-invasive nature. Full recovery from mild, short-term side effects occurs within days or weeks. Any persistent or new symptoms, like residual balance issues or changes in sensation, are monitored and managed by the healthcare team, including neurosurgeons, radiation oncologists, and audiologists.