Overview of Acoustic Neuroma Treatment

An acoustic neuroma, also known as a vestibular schwannoma, is a benign growth that occurs on the vestibulocochlear nerve of the brainstem. Though these growths are always non-cancerous, they can lead to symptoms such as hearing loss, tinnitus, and balance problems. In addition, acoustic neuromas can eventually press against your surrounding brain tissues, nerves, and brainstem. Fortunately, they grow very slowly. 

Despite their slow growth rate and generally favorable prognosis, discussing treatment with your physician and surgeon is vital. Several options for treating an acoustic neuroma include surgery, radiation therapy, chemotherapy, and observation. The approach will depend on circumstances such as your age, general health, the size of the tumor, and your personal preference.

Knowing these treatment options will allow you to understand what to expect from each option. This article aims to provide an overview of each treatment approach so you can make informed decisions.

There are three main types of surgeries (craniotomies) for removing (resecting) an acoustic neuroma. A craniotomy is any procedure where a small window of bone is temporarily removed from the skull to access the brain for an operation. Due to the acoustic neuroma's location, surgeries to remove it are often performed around the ear. There are three main approaches to accessing the tumor:

• A retrosigmoid craniotomy involves creating an incision behind the ear to remove larger tumor. By placing the incision behind the ear, the surgeon can access both the internal auditory canal and the cistern, which is the area where the auditory nerves connect to the brain. When performed successfully, this procedure allows the patient to retain their hearing and the function of their facial nerves.
• A middle fossa craniotomy occurs when the surgeon makes an incision above the ear. This method is primarily used for smaller acoustic neuromas and is optimal when the growth is mainly found in the internal auditory canal rather than in the cistern. This approach may also preserve hearing.
• For a translabyrinthine craniotomy, an incision is made behind the ear. However, unlike with a retrosigmoid craniotomy, the surgeon must remove some of the inner ear bone during this procedure to reach the tumor. This type of craniotomy is only performed in cases of larger acoustic neuromas and when hearing is already significantly compromised.

As with many tumors, radiation therapy for acoustic neuroma is an option available to patients. Recent advancements in radiation technology have made radiation therapy more powerful and precise than ever. Stereotactic radiation can either be delivered as single-fraction stereotactic radiosurgery (SRS) or by dividing the radiation treatment over multiple sessions, also called fractionated stereotactic radiotherapy (FRS). Both types of radiation (SRS and FSR) work similar to each other by damaging the DNA of the tumor cells. Both SRS and FSR are conducted in the outpatient setting and do not require either general anesthesia or a hospital stay.

Small and even some of the mid-size tumors are reasonable candidates for this mode of treatment. In such cases, radiotherapy is effective and associated with long-term control of the tumor. Therefore, an increasing number of patients have chosen to use stereotactic radiosurgery as the primary treatment for their acoustic neuroma.

The common approaches to radiation therapy for acoustic neuromas include:

• Stereotactic radiosurgery: Also known as GammaKnife®, this minimally invasive procedure delivers radiation beams directly to the tumor with little effect on the surrounding tissues.
• Linear Accelerator (LINAC) systems work by accelerating electrons to produce high-energy X-rays. The beam of X-rays (photons) is then conformed to the tumor. The LINAC machines are produced by a variety of different manufacturers with common trade names including CyberKnife®, Trilogy®, Novalis Tx™, and TruBeam™ among others.

Proton Beam systems use a particle accelerator to generate precise and accurate radiation energy in the form of protons which can be delivered to the tumor.

It is important to note that all systems have relatively similar outcomes, and the patient should not be confused or frustrated by the different choices. The treatment team consists of a neurosurgeon and a radiation oncologist. Acoustic neuromas that are greater than 2.5 – 3 cm in size are not ideal candidates for radiation therapy and surgery is usually the preferred option.

In very rare cases, if surgery and radiation therapy aren't viable for treatment, chemotherapy and medical management of acoustic neuromas may be considered. Chemotherapy and medications are not as effective as other options. Because acoustic neuromas tend to be benign and slow-growing, chemotherapy isn't commonly used to treat them. However, some patients develop a rare hereditary form of vestibular schwannoma where the tumor either doesn't stop growing or grows in both ears. Physicians may choose chemotherapy as a treatment method for these very rare tumors.

Some drugs have been used to treat acoustic neuroma with varying degrees of efficacy. Two such drugs, bevacizumab and erlotinib, are the most commonly used medications. Bevacizumab received FDA approval for fighting certain cancers, and it may stabilize the size of acoustic neuromas in cases where removal isn't advisable or possible. Erlotinib has been shown to reduce the growth of schwannoma cells in mice. Still, the results for use on human patients have only been effective for those with acoustic neuromas not caused by hereditary conditions such as neurofibromatosis type 2. 

Many small acoustic neuromas don't cause symptoms and grow at a slow rate, so monitoring tumor growth in select patients suffering from an acoustic neuroma is another viable option. This is often referred to as the "watch and wait" approach. In addition, patients who cannot tolerate surgery, radiation therapy, or chemotherapy are candidates for observation. 

Sometimes, surgical intervention isn't enough to thoroughly remove an acoustic neuroma, and part of the tumor that is attached to the facial nerve is left behind to avoid the risk of permanent facial weakness. The follow-up to these procedures is observation to determine whether the growth will recur. The residual tumor is often monitored every 6-12 months via MRI scans and stereotactic radiosurgery is advised if tumor regrowth is encountered.

There are several methods for treating an acoustic neuroma once one is diagnosed. Your neurosurgeon, otologist (ear doctor), and radiation oncologist will consult with you and perform the necessary tests to help determine the best course of treatment, while respecting your preferences. We recommend a consultation both with a neurosurgeon and a radiation oncologist before final treatment decision is reached. Knowing all the options available for treatment is critical for you to choose the one that is best for you.

• Acoustic neuromas are most commonly treated via surgery or radiation.
• Asymptomatic and residual tumors after surgery may undergo observation and monitoring for tumor growth and regrowth, respectively. Radiation is a reasonable option in these cases.

• Acoustic Neuroma Association 
• Acoustic Neuroma Association of Canada 
• British Acoustic Neuroma Association 
• Vestibular Disorders Association 
• Children’s Tumor Foundation 
• The Alexander Graham Bell Association for the Deaf and Hard of Hearing 
• Hearing Health Foundation 
• American Tinnitus Association