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Acoustic Neuroma Program

Acoustic neuroma is a non-cancerous tumor located at the base of the brain, originating from one of the balance nerves within the internal auditory canal. As it grows, it presses against several nerves and creates problems in hearing, balance, facial movement and facial sensation. Left unchecked, it may press on the brainstem and become life threatening.

Program Details


The cause of acoustic neuromas in most patients is unknown. According to the Acoustic Neuroma Association, estimates of the incidence of symptomatic acoustic neuroma vary from one in every 200,000 people to one in every 3,500 people. Other studies indicate a more frequent incidence, perhaps as high as 1.5% of the population. Most acoustic neuromas are diagnosed on patients between the ages of 30 and 60.

A multidisciplinary team of specialists, including neurosurgeons, otolaryngologists, neurologists, radiation oncologists, neuro-ophthalmologists and rehabilitation specialists provide diagnosis and treatment of acoustic neuromas. For most patients, partial or complete eradication of the tumor is necessary. Surgical options include microsurgery, stereotactic radiation therapy and fractionated radiosurgery.

Surgical Options

The most common option involves microsurgery, in which the tumor is surgically removed. The tumor is accessed through one of three approaches (translabyrinthine, retrosigmoid [suboccipital], or middle cranial fossa). The selection of the approach is based on tumor size and location, as well as the amount of hearing that the patient has before surgery.

Microsurgery is performed using high-powered microscopes and delicate surgical instruments. The surgery usually lasts between 4 to 12 hours and involves an experienced neurosurgeon and otolaryngologist (neuro-otologist) team who perform the surgery together. Hospital stays range from four to seven days, with an average of four to six weeks recovery time.

The second surgical option is radiosurgery, or stereotactic radiation therapy, a non-invasive procedure that uses high-dose-rate radiation to destroy the tumor. Unlike conventional radiation therapy, in which multiple doses of radiation are delivered over several weeks of treatment, radiosurgery involves only a single dose-delivered to the precise location of the tumor.

The third option is fractionated radiosurgery, in which multiple fractions of radiation-delivered at varying angles-are focused on the tumor site. The Froedtert & the Medical College of Wisconsin Neuroscience Research Center is the first in Wisconsin to have advanced Gamma Knife technology available for this use. The Gamma Knife unit is the world standard for superselective irradiation of tumors and uses advanced imaging technology to identify the exact size, shape and location of the tumor. Once the tumor has been pinpointed, the Gamma Knife directs 201 converging beams of radiation on the site, sparing adjacent tissue of clinically significant radiation.

An important characteristic of the Acoustic Neuroma Program is that a surgical team approach is used not only for the microsurgical removal of tumors but also for the stereotactic radiosurgical treatment of tumors.

This collaborative approach utilizing the expertise of a neuro-otologist and neurosurgeon team is designed to enhance clinical outcomes.

In addition to the Gamma Knife, the surgical team has access to a LINAC-based radiosurgery system. In this system, a relocatable, mask-based, stereotactic head ring is used to direct the fractionated radiation beams. The system uses the same stereotactic localizing technique as used for Gamma Knife treatments, thereby assuring that the radiation dose tightly conforms to the shape of the targeted tumor. The fractionated LINAC-based system is typically used for tumors that are too large to be treated using Gamma Knife technology.

All three surgical options are available within the Froedtert & the Medical College of Wisconsin Neuroscience Center. Medical and surgical specialists are available to consult with patients and help them choose the most appropriate treatment option.

Additional Information

Gamma Knife Treatment

The Gamma Knife has been in use worldwide for more than a decade and has been proven to be an effective tool in more than 80,000 radiosurgical treatments. Most often, it is used to treat brain tumors (malignant and nonmalignant), acoustic neuromas and blood vessel abnormalities in the brain.

The Leksell Gamma Knife® is an effective, non-invasive alternative or supplemental treatment to traditional brain surgery. This highly sophisticated technology precisely directs focused radiation to specific targets in the brain. Typically performed in a single outpatient treatment session without general anesthesia, this proven stereotactic radiosurgical procedure helps patients avoid incisions, blood loss, scarring, and long hospital stays while minimizing surgical complications. For many conditions, Gamma Knife treatment is the most accurate form of stereotactic radiosurgery available.

Conditions treated with Gamma Knife Radiosurgery
  • Malignant tumors – metastatic tumors (cancer spread to the brain), gliomas, chondrosarcoma
  • Benign tumors – acoustic neuromas(vestibular schwannomas), meningiomas, pituitary adenomas
  • Vascular abnormalities – arteriovenous malformations (AVMs)
  • Functional disorders – trigeminal neuralgia (also known as tic douloureux or chronic facial pain)
Frequently Asked Questions

What is the Gamma Knife®?

The Gamma Knife is not actually a knife at all. It is a stereotactic radiosurgical device that non-invasively treats malignant and benign brain tumors, vascular malformations and trigeminal neuralgia in a single patient visit. Patients are treated on an out-patient basis or may require an overnight hospital stay.

How does the Gamma Knife work?

Utilizing advanced diagnostic imaging and three-dimensional treatment planning software, Gamma Knife delivers 201 precisely focused beams of gamma radiation to small targets inside the brain. Radiation is only delivered at a single, finely focused point where all 201 beams converge to treat the diseased tissue, while nearby healthy tissue is spared.

What are the benefits of Gamma Knife radiosurgery?

Gamma Knife treatment has many benefits. It is bloodless, virtually painless, no loss of hair and rapid return to pre-treatment activities. Gamma Knife treatment also has excellent, well-documented clinical outcomes for a variety of brain diseases and disorders. This single day procedure is usually covered by most major health insurance companies and Medicare. Due to these benefits, Gamma Knife treatment may replace traditional surgery or radiation therapy, where deemed appropriate by the treatment physicians. However, Gamma Knife treatment is also often used in conjunction with traditional surgery and radiation.

In some cases, Gamma Knife treatment may replace brain surgery or other traditional treatment methods in some patients with brain tumors, vascular malformations and facial pain. An individual who would be at risk for complications from conventional surgery may be a candidate for Gamma Knife radiosurgery. Gamma Knife treatment can be used when prior surgery or radiation therapy has failed to control the disease process. It can also be used in conjunction with conventional surgery in previously inoperable cases, with other forms of radiation therapy and chemotherapy.

While Gamma Knife radiosurgery is a form of radiation treatment, it has several differences from conventional radiation therapy for the brain. Gamma Knife treatment is only directed to targeted areas and spares unnecessary treatment of adjacent, normal brain tissue. Only a one-day treatment is required rather than many treatments over several weeks, and the treatment often can be repeated if necessary. Gamma Knife can also be used in combination with other forms of radiation therapy.

What if I'm older or have other medical conditions?

Gamma Knife radiosurgery is especially valuable for patients whose neurological disorders require a difficult surgical approach or may be impossible to treat using conventional neurosurgical techniques. Patients of advanced age or in poor medical condition can be at an unacceptably high risk for anesthesia and conventional surgery, making Gamma Knife treatment an ideal solution. Gamma Knife technology also is highly beneficial for patients whose lesions are situated in an inaccessible or functionally critical area within the brain. In addition, the treatment can be used as an adjunct to the care of a patient who has undergone conventional brain surgery, interventional neuroradiology or conventional radiation therapy or chemotherapy.

What conditions can be treated by the Gamma Knife?

Conditions that can be treated by the Gamma Knife include:

Malignant tumors such as:

  • Metastases (cancer that has spread to the brain)
  • Malignant gliomas

Benign tumors such as:

  • Meningiomas
  • Acoustic neuromas (vestibular schwannomas)
  • Pituitary tumors
  • Low-grade glioma and skull-based tumors

Vascular malformations such as:

  • Arteriovenous malformations (AVMs)
  • Cavernous angiomas (cavernous malformations)
  • Functional disorders such as:
  • Trigeminal neuralgia

How are patients referred for Gamma Knife treatment?

Most patients are referred to the Gamma Knife program by their doctors. However, some make self-referrals. The Gamma Knife team reviews each patient’s records to determine if Gamma Knife treatment would be advantageous for each patient.

What information is used to determine if Gamma Knife treatment is appropriate?

The Gamma Knife team uses the following information to make its recommendations:

  • Medical and surgical history
  • Clinical examinations
  • Imaging studies, such as MRI, CT and/or PET scans

Is Gamma Knife treatment effective?

The Gamma Knife’s success rate is impressive. Supported by more than two decades of clinical research, this neurosurgical tool has met with unprecedented results. Clinical applications continue to grow, and its many benefits as a non-invasive treatment modality continue to make it the treatment of choice for certain clinical conditions.

What happens during Gamma Knife treatment?

First, a lightweight frame is attached to the patient’s head. Local anesthesia is used before the frame is secured in place. The patient then has an MRI imaging study or, in the case of an arteriovenous malformation, angiography, may be needed in order to precisely locate the diseased area. Data from the imaging study is transferred into the sophisticated treatment planning computer. While the patient rests, the treatment team (a neurosurgeon, radiation oncologist and physicist) uses advanced software to determine the treatment plan. This planning usually takes one or two hours to complete, depending on the complexity and location of the disease. When the individual treatment plan is completed, the patient is placed on the Gamma Knife couch and precisely positioned. The patient is then moved automatically, head first into the machine, and treatment begins. Treatment typically lasts from 15 minutes to over an hour, depending upon the complexity of the case and location of the target. The patient does not feel or see the treatment. Following treatment, the patient is automatically moved out of the machine, and the head frame is removed.

What will I feel during Gamma Knife treatment?

During the actual treatment, the patient feels nothing unusual. The patient does not see or feel the radiation during treatment. Prior to the actual treatment, patients typically feel slight discomfort from the local anesthetic used when placing the head frame, and some patients have reported feeling pressure for a short time while the pins are inserted to fixate the head frame- but no pain is experienced during the treatment process.

Will I be awake during the procedure?

The patient remains conscious throughout the entire procedure and may communicate with the treatment team.

Will my head be shaved?

No, the head is not shaved. In rare cases the treatment may cause some hair loss.

What can I expect after treatment?

When the treatment is finished, the head frame will be removed. Sometimes there is a little bleeding from where the pins were placed on the head. In this case, gauze and pressure will be applied to stop the bleeding and keep the area clean. A temporary head dressing is placed to keep the pin sites clean. It is recommended that the patient take it easy over the next 12 to 24 hours. Pre-Gamma Knife activities can be resumed within a few days.

Is Gamma Knife treatment safe?

The Gamma Knife allows non-invasive brain surgery to be performed with extreme precision while sparing healthy tissues surrounding the targeted treatment area. Also, because neither a surgical incision nor general anesthesia is required, the risks usually involved with open brain surgery, such as hemorrhage or infection, may be reduced. Hospitalization is rarely required and recovery time is minimal. While individual patient outcomes may vary, patients may resume their normal pre-surgery lifestyle within a few days.

How quickly will the treatment work?

The effects of Gamma Knife radiosurgery occur over several days to several years, depending on the type of medical condition treated. The radiation alters the DNA of the tumor or lesion being treated so that the cells no longer reproduce, eventually rendering the lesion static. Some abnormalities dissolve gradually, eventually disappearing. Others simply exhibit no further growth. The effectiveness of the treatment is monitored by MRI scans at regular intervals. The goal of radiosurgery is tumor control, which is defined as stable tumor size or tumor shrinkage. For vascular malformations, control is generally considered total obliteration.

What are the complications of Gamma Knife treatment?

Early complications may include:

Common side effects:

  • Local pain and swelling in the scalp
  • Headache
Rare complications:
  • Skin reddening and irritation
  • Nausea
  • Seizure

Delayed complications may include:

Uncommon complications:

  • Local loss of hair in superficial lesions
  • Local brain swelling in the treatment site
  • Local tissue necrosis in the treatment site

Rare complications:

  • Visual loss (dependent on diagnosis and areas treated)
  • Hearing loss (dependent on diagnosis and areas treated)

When can I return to my normal activities?

Within a few days. The only restrictions you will have are the same you had prior to your treatment.

Is Gamma Knife treatment more or less expensive than traditional brain surgery?

Cost studies have shown Gamma Knife radiosurgery to be less expensive than conventional neurosurgery because it eliminates lengthy post-surgical hospital stays, expensive medication and potentially months of rehabilitation. Importantly, there are virtually no post-surgical disability and convalescent costs with this procedure.

Will my insurance cover this procedure?

Gamma Knife radiosurgery is reimbursed by most insurance companies, PPOs, HMOs and Medicare.



David R. Friedland, MD, PhD

Associate Director, Director, Chief, Professor


John S. Rhee, MD, MPH

Professor & Chair