Use of
Gamma Knife technology for acoustic neuroma

An acoustic neuroma (vestibular schwannoma) is a rare benign tumor that originates in the vestibular and auditory nerves. One in 50,000 people suffer from this disease annually; the causes are unknown. Women are affected slightly more often than men.

The tumor starts to develop in the internal auditory canal. From here it grows slowly toward the cerebellar tissue and widens the bone of the inner auditory canal over time. People aged between 40 and 60 years old are most often affected. With small tumors the patient often has no symptoms whatsoever for many months to years. This kind of tumor grows around 1–5 mm a year – it is normally not hereditary.

One exception is neurofibromatosis type II disease. This extremely rare form with bilateral acoustic neuromas and meningiomas affects young people. Inheritability has been proven with this condition.

Initial symptoms include tinnitus in one ear, hearing loss or occasionally sudden loss of hearing, as well as the occurrence of dizziness or slight unsteadiness, particularly with a rapid change of position and when walking in the dark.

Diagnosis

MRI provides the best examination procedure to diagnose an acoustic neuroma. This provides important information, such as tumor size and location in relation to the cranial nerves and brain stem. A contrast-enhanced thin-slice MRI (1–1.5 mm) is performed.

The three relevant cranial nerves are the cochlear nerve, the vestibular nerve, and the facial nerve. Individual nerve tracts of these cranial nerves can usually no longer be imaged clearly with a tumor located in the internal auditory canal.

More than 90% of all patients with acoustic neuroma lose hearing on the affected side within 10 years of diagnosis if left untreated. An ENT physician should carry out regular hearing tests (audiometry) to assess hearing impairment. Once tumor pressure damages the hearing, treatment can no longer restore the hearing loss.

Wait-and-see

With very small tumors, i.e. less than 1 cm, the spontaneous course can be observed using MRI checkups (wait-and-see). However, you should not wait too long as otherwise permanent hearing damage, i.e. deafness, may occur.

Surgery

Surgery is the primary procedure for large tumors over 2.5–3 cm in diameter. Surgery removes the tumor and eliminates the compression on the brain tissue. The operation is performed under full anesthesia and lasts on average 3–5 hours. Risks primarily consist of hearing impairment through to loss of hearing. In the initial period, significant balance problems and sometimes also facial weakness occur. Serious risks (5%) of this kind of operation include bleeding, secondary bleeding, infection, accumulation of cerebrospinal fluid, or tissue injuries.

Following surgery, the vestibular nerve is destroyed and the patient has balance problems for 2–3 months.

Facial paralysis (facial nerve) is more likely following surgery than following radiosurgery. Permanent facial paralysis may occur with nerve damage.

Radiation therapy

Radiosurgery is an alternative to surgery for smaller acoustic neuromas. Here the tumor is not removed, but killed. Unlike surgery, the skull is not opened. Whether radiosurgery is possible will depend on the size and location of the tumor.

Radiation therapy

Single-dose ultra precise radiosurgery has become the solution of choice for small and medium-size tumors. Unlike fractionated radiation therapy over several weeks, our Gamma Knife therapy targets the tumor with pinpoint accuracy. It also optimally protects the area surrounding the tumor thanks to the very steep dosage reduction.

Outcome

Our radiation therapy aims to stop the tumor. This is possible in around 90–95% of patients. Treated tumors shrink substantially in approximately 40–60% of cases 1–2 years after radiosurgery.

In around 20–25% of irradiated acoustic neuromas this can cause slight swelling temporarily. In the initial MRI checkups the tumor may therefore appear slightly enlarged despite the lack of actual growth. This swelling spontaneously goes down.

Risks

There is a 20–40% risk of hearing impairment or deafness in the affected ear. This will depend on the size and location of the acoustic neuroma.

Weakness of the facial nerve is extremely rare (1–2%). Balance problems are a common temporary symptom following radiation therapy (5%). Training and compensation from the healthy side will usually help relieve dizziness.

Reliable radiosurgery with pinpoint accuracy on the brain requires fixation of the head during treatment. Either using a stereotactic ring or a thermoplastic mask.

There is normally no need to stay in hospital when using the Gamma Knife for radiosurgery. Exceptions occur whenever the patient requires in-hospital care and monitoring due to comorbidity. In these cases, this involves a short hospital stay. There is no need for convalescent care or rehabilitation.

Following surgery on an acoustic neuroma, the patient will be unfit for work for 2–3 months and should avoid physical exertion in this period. But after radiation therapy with our Gamma Knife patients can normally return to work after 2–3 days, perform everyday household chores, and exercise again after a week or so.

Necessary aftercare following radiosurgery includes MRI checkups every 4–6 months initially and later annually. Regular hearing tests (audiometry) by the ENT physician are recommended to check hearing in future.

Aftercare aims to detect renewed tumor growth or a residual tumor early on, as well as detecting subsequent side effects. This applies to radiosurgery and to conventional surgery.

Gamma Knife as a safe alternative to surgery

Radiosurgery with our Gamma Knife is a very effective, safe therapy as an alternative to surgery in the case of an acoustic neuroma, particularly for small and medium-sized tumors.