Surgery Basics

Physicians may choose surgery for people with large tumors or tumors that are causing serious problems with balance, persistent headaches or facial pain, or hydrocephalus, a buildup of fluid in the brain.

Hydrocephalus occurs when an acoustic neuroma grows large enough to press on the brain stem, the lower portion of the brain that connects to the spinal cord. This blocks the flow of cerebrospinal fluid—the liquid that surrounds and cushions the brain and spinal cord—from draining properly.

Very small tumors can also be treated with surgery when doctors observe growth or when preservation of hearing is a goal.

Surgery to remove an acoustic neuroma is often guided by computer software that incorporates MRI scans and CT scans, which create three-dimensional images of the brain. The imaging tests help surgeons remove tumors with great precision, while avoiding damage to nerves responsible for hearing, balance, and facial movement.

Surgical Approach Overview

How do you decide which type of surgery is right for you? The surgical approach your doctor uses depends on the tumor size and location and whether preserving your hearing is a priority or an option. All procedures require general anesthesia.

The surgery is performed by a team of physicians including a neurotologist (ear and skull base surgeon) and a neurosurgeon. There are three main microsurgical approaches for the removal of an acoustic neuroma: translabyrinthine, retrosigmoid/sub-occipital and middle fossa. The approach used for each individual patient is based on several factors such as tumor size, location, skill and experience of the surgeon, and whether or not hearing preservation is a goal. The surgeon and the patient should thoroughly discuss the reasons for a selected appoach. Each of the surgical approaches has advantages and disadvantages, and excellent results have been achieved using all three of the techniques.

Figure 2. Three surgical approaches to an acoustic neuroma: retrosigmoid/sub-occipital, translabyrinthine and middle fossa. 

(Printed with permission of the Mayfield Clinic - www.mayfieldclinic.com) 

Translabyrinthine Approach

Doctors may use translabyrinthine surgery for any size of tumor that has caused significant hearing loss or where hearing preservation is not possible. During this procedure, the surgeon makes an incision behind the ear and opens the mastoid bone, as well as a portion of the inner ear, which contains structures important for hearing and balance. This gives the surgeon access to the tumor in the internal auditory canal, which acts as the passageway for the eighth cranial nerve—the nerve that runs from the brain to the inner ears—and provides a good view of the nerves so the surgeon can preserve facial function.

The surgeon removes the entire tumor, or as much of it as is safely possible. To reach the tumor, surgeons occasionally remove the cochlea, the part of the inner ear that processes sound, or the otic capsule, which is the bony structure that surrounds the inner ear.

Because a portion of the inner ear is removed during this procedure, hearing is lost in that ear. Balance is usually not a problem because the opposite ear can take over this function, although rehabilitation therapy may be necessary to help you compensate for some loss of balance.

In general, the translabyrinthine approach is the best option when hearing has already been severely affected from the tumor or when tumors are large and hearing preservation is not possible.

Retrosigmoid Approach

Surgeons may use a retrosigmoid approach for smaller acoustic neuromas when hearing preservation is possible. They use this approach for tumors that are growing out of the internal auditory canal and approaching the brainstem.

During this surgery, a surgeon makes an incision further behind the ear to open a portion of the skull called the occipital bone, located behind the mastoid. The cerebellum, a part of the brain located above the brain stem, falls back out of the way, and surgeons remove the bone over the internal auditory canal to fully access the tumor. The surgeons can view the facial nerve, the hearing nerve, and the brainstem.

If removing the entire tumor could damage nerves or brain tissue, the doctor may leave some small bits of the tumor behind. The section of the skull opened to perform this surgery is replaced after tumor removal. Fat from the periumbilical region, meaning the area surrounding the belly button, may be removed and used to seal the closure to prevent spinal fluid leaks.

Middle Fossa Approach

The middle fossa approach is an option for smaller tumors that have not grown beyond the internal auditory canal. As with the retrosigmoid approach, it is used to help preserve hearing. The surgeon makes an incision above the ear in the lateral skull bone, and then uncovers the internal auditory canal, and removes the acoustic neuroma. Then surgeons replace the skull bone and use fat from elsewhere in the body to help close the opening. This approach is the best for saving hearing, which is possible in the majority of people who have the procedure.

Subtotal, Near Total and Total Removal

Subtotal Removal:

Subtotal removal is indicated when anything further risks life or neurological function. In these cases the residual tumor should be followed for risk of growth (approximately 35%). If the residual tumor grows further, treatment will likely be required. Periodic MRI studies are important to follow the potential growth rate of any tumor. 

Older patients with large tumors causing a threat to life may elect to have their surgeon sub-totally remove their tumor. Partial tumor removal has also been advocated in some patients who have large tumors in their only hearing ear. This surgical management will reduce the tumor in size, so that it may cause no threat to the patient's health during his or her life expectancy. This approach may reduce the probability of facial nerve dysfunction as a result of the surgery.

Near Total Tumor Removal:

This approach is used by experienced centers when small areas of the tumor are so adherent to the facial nerve that total removal would result in facial weakness. The piece left is generally less than 1% of the original and poses a risk of regrowth of approximately 3%. Periodic MRI studies are important to follow the potential growth rate of any tumor.

Total Tumor Removal:

Many tumors can be entirely removed by surgery. Microsurgical techniques and instruments, along with the operating microscope, have greatly reduced the surgical risks of total tumor removal. Preservation of the facial nerve to prevent permanent facial paralysis is the primary task for the experienced acoustic neuroma surgeon. Preservation of hearing is an important goal for patients who present with functional hearing. Both facial nerve function and hearing is electrically monitored during surgery. This is a valuable aid for the surgeon while the tumor is being removed.

Figure 1. Comparison of partial and total tumor removal. Every effort is made to remove the tumor without damaging the adjacent nerves or vital brainstem functions. Sometimes it may be best to leave small pieces of tumor capsule attached to critical structures rather than risk damage. If over time the tumor remnant grows, futher treatment is warranted. (Printed with permission of the Mayfield Clinic – www.mayfieldclinic.com)

Preparing for AN Surgery (pdf)

Preparing for AN Surgery

What to Expect after Surgery

After surgery, you may spend a few days recovering in the hospital while your doctor monitors you and manages any pain, dizziness, and other symptoms you may be experiencing. If your hearing has been affected by the surgery, your doctor can work with you to explore your options for hearing rehabilitation. Balance is recovered slowly, and most people can return to work in 8 to 12 weeks.

 
This presentation was part of our ANAwareness Week event hosted by UC San Diego. View the rest of this presentation and many others in our Video Library.

Acoustic Neuroma Surgical Options

Translabyrinthine Approach

Doctors may use translabyrinthine surgery for any size of tumor that has caused significant hearing loss or where hearing preservation is not possible. During this procedure, the surgeon makes an incision behind the ear and opens the mastoid bone, as well as a portion of the inner ear, which contains structures important for hearing and balance. This gives the surgeon access to the tumor in the internal auditory canal, which acts as the passageway for the eighth cranial nerve—the nerve that runs from the brain to the inner ears—and provides a good view of the nerves so the surgeon can preserve facial function.

The surgeon removes the entire tumor, or as much of it as is safely possible. To reach the tumor, surgeons occasionally remove the cochlea, the part of the inner ear that processes sound, or the otic capsule, which is the bony structure that surrounds the inner ear.

Because a portion of the inner ear is removed during this procedure, hearing is lost in that ear. Balance is usually not a problem because the opposite ear can take over this function, although rehabilitation therapy may be necessary to help the patient compensate for some loss of balance.

In general, the translabyrinthine approach is the best option when hearing has already been severely affected from the tumor or when tumors are large and hearing preservation is not possible.

Pros:

• Oldest approach - longest history
• Approach facilitates identification of facial nerve for preservation
• Allows for excellent exposure of the internal auditory canal and tumor
• Any size tumor can be removed with this approach.

Con:

• Results in permanent and complete hearing loss on tumor side

Retrosigmoid Approach

Surgeons may use a retrosigmoid approach for smaller acoustic neuromas when hearing preservation is possible. They use this approach for tumors that are growing out of the internal auditory canal and approaching the brainstem.

During this surgery, a surgeon makes an incision further behind the ear to open a portion of the skull called the occipital bone, located behind the mastoid. The cerebellum, a part of the brain located above the brain stem, falls back out of the way, and surgeons remove the bone over the internal auditory canal to fully access the tumor. The surgeons can view the facial nerve, the hearing nerve, and the brainstem.

If removing the entire tumor could damage nerves or brain tissue, the doctor may leave some small bits of the tumor behind. The section of the skull opened to perform this surgery is replaced after tumor removal. Fat from the periumbilical region, meaning the area surrounding the belly button, may be removed and used to seal the closure to prevent spinal fluid leaks.

Pros:

• Possible preservation of hearing 
• Approach provides a good view of the AN in relation to brainstem
• Possible preservation of facial nerve
• Any size tumor can be removed with this approach.

Cons:

• Hearing preservation decreases if the tumor is large.
• Headaches are a more prevalent post-op side effect.

Middle Fossa Approach

The middle fossa approach is an option for smaller tumors that have not grown beyond the internal auditory canal. As with the retrosigmoid approach, it is used to help preserve hearing. The surgeon makes an incision above the ear in the lateral skull bone, and then uncovers the internal auditory canal, and removes the acoustic neuroma. This approach is the best for saving hearing, which is possible in the majority of people who have the procedure. Then surgeons replace the skull bone and use fat from elsewhere in the body to help close the opening.

Pro:

• Possible preservation of hearing with small tumors in the right location, typically confined to the internal auditory canal

Con:

• Most often used only with small tumors, typically confined to the internal auditory canal.

Radiation Treatment Options

Stereotactic radiation can either be delivered as single-fraction radiosurgery (SRS) or by dividing the radiation dose over multiple sessions which is termed fractionated stereotactic radiotherapy (FRS). Both forms of radiation (SRS and FSR) work similarly by damaging the DNA within the tumor cells. The cells can no longer divide and eventually die over time, a process called necrosis. Both techniques are performed in the outpatient setting and do not require either general anesthesia or a hospital stay.

Over the last several decades, as the technologies for delivering stereotactic radiation have improved, an increasing number of patients have chosen to receive stereotactic radiosurgery as the primary treatment for their acoustic neuroma. There are several different commercially-available machines that are used to treat acoustic neuromas with the technologies differing in their source of radiation and how the radiation is precisely delivered.

• Gamma Knife® machines derive their radiation from a fixed-array of Cobalt-60 sources. These machines are typically used to deliver SRS in a single-session, although the newest platform (Leksell Gamma Knife® Icon™) allows for fractionated delivery (FRS).
• Linear Accelerator (LINAC) machines work by accelerating electrons to produce high-energy X-rays. The beam of X-rays (photons) is then shaped to the tumor as it exits the machine using a series of collimators and by rotating either the patient or the machine. LINAC machines are produced by a variety of different manufacturers with common trade names including CyberKnife®, Trilogy®, Novalis Tx™, and TrueBeam™ among others, with each machine available for both single-session (SRS) and multi-session (FSR) treatment.
• Proton Beam machines use a particle accelerator to generate radiation energy in the form of protons which can be delivered as either SRS or FSR.

Despite their differences, similar results in terms of effectively treating acoustic neuromas and avoiding side effects have been reported for each of the stereotactic radiation machines. The treatment team should consist of a neurosurgeon and/or a neurotologist and a radiation oncologist. The patient and the treatment team typically consider a number of factors before determining whether radiation therapy is appropriate including the size of the acoustic neuroma and the rate at which it is growing, the patient’s age and overall health, and the patient’s symptoms including the degree of hearing loss, balance problems, and vertigo. Typically, acoustic neuromas that are greater than 2.5 – 3cm in size are not considered ideal candidates for radiation therapy as these larger tumors often compress the surrounding brainstem and the potential for side effects from the radiation is increased.

Advantages of Surgery

• Surgery removes the tumor for those who want it "out of their body."
• Some patients have a fear of very rare, long term effects of radiation, such as induced malignancy.
• Size and/or position of the tumor may make radiation inadvisable, due to post-treatment swelling.
• Radiation may not be recommended for tumors larger than 2.5 to 3 cm.
• Younger age is generally another determining factor for choosing surgery.
• Sub or near-total tumor resection followed by radiation may be considered.

Advantages of Radiation

• Good option for patients in their mid-50's and older or with health issues.
• Radiation is typically an outpatient procedure, though some patients may stay in the hospital overnight. The radiation session itself is relatively quick. Some procedures are done in one session and others take several sessions.
• There is usually no need to take time off from work. Some people are treated on their way to or from work when having multiple sessions.
• There is no recuperation or convalescence time immediately after treatment.
• There are usually no immediate complications. In the medium term, there may occasionally be complications as radiation takes time to fully present symptoms.

Advantages of Observation

• Good option for small tumors, especially in older individuals; AN may not grow and may not require treatment.
• Hearing may be preserved longer in cases where the tumor presents on the only hearing side.
• All medical treatments, surgical or radiation, carry some risks. As ANs are benign and grow very slowly, many physicians will recommend having a second MRI at least 6 months after the first, to establish the growth rate. If the tumor is not growing, avoiding treatment altogether is a possibility.
• In time, safer treatments for acoustic neuromas, other than surgery or radiation, may be found.
• There are no known ways to cure or shrink an acoustic neuroma naturally.

What To Expect

Due to expanded use of MRIs, many acoustic neuroma tumors are discovered when they are relatively small. Because of this and the fact that acoustic neuromas are non-cancerous, the patient and caregivers typically have time to do thoughtful research on treatment options and medical providers. The ANA recommends getting more than one medical opinion about treatment whenever possible. It is also important to learn how various treatments will affect short and long-term quality of life. Depending on a variety of factors, a patient may be more concerned with hearing preservation, facial function, or other side effects.

Surgery

Surgery for an acoustic neuroma is performed under general anesthesia and involves removing the tumor through the inner ear or through a window in your skull. The entire tumor may not be able to be completely removed in some cases. For example, if the tumor is too close to important parts of the brain or the facial nerve.

Surgery can create complications, including worsening of symptoms, if certain nerve or cranial structures are affected during the operation. These risks are often based on the size of the tumor and the surgical approach used.

After surgery, the patient may spend a few days recovering in the hospital while doctor monitor and manage any pain, dizziness, and other symptoms the patient may be experiencing. If hearing has been affected by the surgery, the doctor can work with the patient to explore their options for hearing rehabilitation. Balance is recovered slowly, and most people can return to work in 8 to 12 weeks. (Included with permission by NYU Langone www.nyulangone.com.)

Radiation

If the decision is made to move forward with radiation, the treatment process usually begins by defining the radiation target using an MRI with gadolinium to visualize the acoustic neuroma. The stereotactic radiation planning software is then used to create a 3-dimensional model of the tumor and the surrounding structures. The treatment team along with a radiation physicist then creates dosimetry maps showing the level of radiation to be received by the tumor and the normal tissues and the treatment plan is optimized to focus the radiation as precisely as possible to the acoustic neuroma. The patient’s head is then stabilized with either a molded mask shield or a metal frame that is pinned to the skull. The type of stabilization device and the length of treatment depend on the stereotactic radiation machine being used, but treatments generally last between 30 -120 minutes for SRS and approximately 10-15 minutes for each treatment fraction with FSR.

Once radiation has been used to treat the acoustic neuroma, surveillance imaging, typically with MRI scans, should be performed for at least 10 years after the treatment to ensure that the tumor does not continue to show any signs of growth that would require further treatment.

Observation

Observation has become an accepted ‘treatment’ option for acoustic neuroma when the tumor is small, the patient is asymptomatic, is elderly, or the patient is averse to treatment. Many patients choose to observe their tumor for some period of time before considering treatment.

Monitoring will likely continue with periodic MRIs and other tests; surgery or radiation treatment may be recommended if there is tumor growth and/or an increase in symptoms. Doctors may also recommend treatment to preserve hearing, facial function, or other factors.

The Newly Diagnosed Handbook patient booklet has more detailed information about treatment options.