Acoustic Neuromas

Vestibular Schwannoma (Acoustic Neuromas)

Acoustic Tumor

The diagnosis of a cerebellopontine angle tumor has been made.  Most likely, this is a vestibular schwannoma (also known as an acoustic neuroma or acoustic tumor).

General Comments

Vestibular schwannomas are benign growths originating from the balance nerve. Unlike cancer which can spread throughout the body and start growing, benign tumors do not spread. They grow where they are.  Since these tumors are deep inside the skull and are adjacent to vital brain centers, they may cause significant problems as they grow.

The first signs or symptoms one notices are usually related to ear function.  These include tinnitus (ringing in the ear), hearing loss, and balance issues.  As they continue to enlarge, they involve other surrounding nerves and the brainstem.  This may lead to numbness of the face, headache, problems walking, and increased pressure in the head.  If allowed to continue over a long period of time, it may be fatal.

In most cases, the tumors grow slowly over a period of years.  Typical growth rate is 1-2 millimeters a year.  In others, the rate of growth is more rapid. 

As imaging has improved, and screening, these tumors are being identified earlier while they are smaller.  This earlier diagnosis allows for more management options.  Initially, great effort was exerted just to preserve life following surgery.  As surgical techniques have improved, and with earlier diagnosis, the goal of surgery now is to preserve normal function of the cranial nerves.

Options

There are many factors which must be considering when determining the best way to manage vestibular schwannomas.  Size of the tumor, age of the patient, amount of hearing loss, presence of dizziness all must be considered.

Size of the Tumor

Risks and complications of acoustic tumors vary with the size of the tumor.  We classify tumors as small, medium and large.  The larger the tumor the more serious the complications and the higher likelihood complications will occur.

Small Tumor

A small vestibular schwannoma is still confined within the bony canal that extends from the inner ear to the brain.  It is through this canal that the hearing, balance, and facial nerves pass.

Medium Tumor

A medium sized tumor in one which has extended from the bony canal in the space between the brain and the skull.  But is not yet putting any pressure on the brain itself.

Large Tumor

A large vestibular Schwannoma is one that has extended out of the bony canal and into the space between the brain and skull.  It is sufficiently large enough to put pressure on the brain.

Options

Observation

Since these tumors are slow growing, it is occasionally possible to observe them with serial MRIs.  This will require an MRI every 6 months for the first two years, followed by annual MRIs.  If the patient has good hearing, it is possible that the hearing will decrease even if the tumor does not significantly change in size.  In younger patients, the odds of going throughout a lifetime without the tumor growing is fairly low.  40% - 60% of patients choosing observation will have growth that requires some other form of intervention.

Radiation Therapy

Radiation therapy works by killing rapidly dividing cells.  Since these tumors are slow growing, the radiation does not kill the tumor.  It is intended to keep the tumor from growing by damaging the blood vessels that supply the tumor.  Even after radiation, the tumor is viable so serial MRIs will still be required.  In addition, with radiation therapy the damaging affects to surrounding nerves (including hearing loss and facial weakness) may develop years after radiation.  Dizziness is a major problem for approximately a third of patients who undergo radiation therapy.

Surgical Approaches

The choice of surgical approaches depends up size and location of the tumor, level of residual hearing, and patient age.

Translabyrintine Approach

An incision is made behind the ear.  The mastoid and inner ear structures are removed to expose the tumor.  The tumor is removed.  The mastoid defect is filled with fat harvested from the abdomen and a titanium mesh plate if secured over the defect.  The translabyrinthine approach sacrifices the hearing and balance mechanisms of the inner ear.  Consequently, the ear is made permanently deaf.  Although the balance mechanism has been removed in the operated ear, the patient is able to compensate using the unoperated ear.  This compensation may take 3-4 months.  This approach is suitable for tumors of any size.  No brain retraction is required to remove the tumor.

Middle Fossa Approach

An incision is made above the ear and a window is made in the skull.  The temporal lobe of the brain is elevated and retracted.  Bone is removed to expose the tumor.  Every effort is made to preserve the hearing nerve while removing the tumor.  A small piece of abdominal fat is placed into the bony defect created.  The bone is repositioned and secured with titanium plates.  In 60% - 70% of cases it is possible to preserve some hearing following tumor removal.  This approach is limited to small and occasionally medium sized tumors.  In addition, it is not suitable for patients over 65 years old.

Retrosigmoid Approach

An incision is made behind the ear.  A small window is made in the skull and the cerebellum is retraced to expose the tumor.  The tumor is removed and every effort is made to preserve the hearing nerve.  In about 50% of the cases it is possible to preserve hearing in the ear.  This approach allows limited exposure of the portion of the tumor that lies within the bony canal.  It associated with a higher rate of persistent post-operative headaches.

Risks and Complications of Vestibular Schwannoma Surgery

In general, the smaller the tumor the lower the risk of complication. 

Hearing Loss

Current technology has made major improvements in hearing rehabilitation.  The unilateral hearing loss that results from vestibular schwannomas may be rehabilitated with a CROS (Contralateral Routing Of Sound) or an Osteointegrated Temporal Bone Implant.

Tinnitus

Ringing in the ear following surgery is difficult to predict.  In many cases, the tinnitus will decrease following surgery.  However, in some cases if increases or remains the same. 

Taste Disturbance and Mouth Dryness

Taste disturbance and mouth dryness is not uncommon for a few weeks following surgery.  In 5% of patients this disturbance is prolonged. 

Dizziness and Balance Disturbance

In vestibular schwannoma surgery it is necessary to remove a portion of the vestibular (balance) nerve and depending on the approach a portion of the inner ear may be removed.  Oftentimes, the tumor has already affected the balance system.  In many cases, dizziness and balance are improved following surgery.  Immediately following surgery, if the tumor has not affected the balance system, the patient may have severe dizziness for a few days following surgery.  Imbalance and unsteadiness may persist for several months until the balance system in the opposite ear, and the brain, are able to compensate.

Facial Paralysis

Vestibular schwannomas are in intimate contact with the facial nerve. The facial nerve is responsible for the movement of the muscles of the face and for closure of the eye.  Temporary partial paralysis of the facial nerve occurs in 10% - 15% of patients following vestibular schwannoma surgery.  This weakness may persist for 6-12 months.  Up to 5% of patients may have some permanent partial paralysis.

Facial paralysis may result from nerve swelling or nerve damage.  Swelling of the facial nerve is common due to the fact that the nerve is usually compressed and distorted by the tumor in the internal auditory canal.  Careful removal of the tumor with the help of a facial nerve monitor and an operating microscope usually result in preservation of the nerve.  However, nerve stretching during tumor removal may result in swelling of the nerve with subsequent temporary paralysis.  In these instances, facial function is observed for a period of months following surgery.  If it becomes certain that facial function will not recover additional procedures may be recommended to help.

In rare cases, the tumor may be found to originate from the facial nerve.  In those cases, the tumor may be removed or decompressed.  It is removed it may require that a portion of the facial nerve be removed along with it.  If that happens it may be possible to reconnect the facial nerve immediately or to take a portion of skin sensation nerve from the neck and replace the missing portion of the nerve.

If the nerve does not recover, other procedures may be recommended to help reanimate the face.

Eye Complications

Should facial paralysis occur the eye may become dry and unprotected.  During the period until facial function recovers, eye care is critical!  An eye specialist will be consulted and other procedures may be required to help protect the eye.  Taping the eye closed and applying drops will be necessary. 

Other Nerve Weaknesses

On rare occasions vestibular schwannomas may contact other nerves as they leave the brainstem.  These nerves may be damaged which may lead to problem with eye movements, swallowing, sensation of the throat, and changes to the voice. 

Post-operative Headache

Headache following vestibular schwannoma removal is common in the early post-operative period.  Generally, is resolves with time.

Brain Complications and Death

Vestibular schwannomas are located adjacent to vital brain centers which control breathing, blood pressure, coordinated movement, and heart function.  As the tumor enlarges it may become attached to these brain centers and may become intertwined with the blood vessels supplying these areas of the brain.  Careful tumor dissection with the help of an operating microscope usually avoids complications.  If the blood supply to vital brain centers is disturbed, serious complications may result.  Including: loss of muscle control, coordination of movement of arms and legs (ataxia), paralysis, even death.

Postoperative Cerebrospinal Fluid Leak

The brain lies within a dense fluid filled sac called the dura.  The fluid surrounding the brain is called cerebrospinal fluid.  The dura is opened to remove the tumor.  After the tumor is removed, the dura is closed and covered with fat from the abdomen.  Occasionally, the cerebrospinal fluid finds a way to leak out following surgery.  If this happens, a drain may be placed in the back to remove cerebrospinal fluid and reduce pressure at the area that is leaking.  Rarely, it may require a return to the operating room to repair the leak.

Postoperative Bleeding and Brain Swelling

Bleeding and brain swelling may develop after vestibular schwannoma surgery.  If this extremely rare complication occurs it will require a return to the operating room to stop the bleeding and allow the brain to expand.

Postoperative Infection

Very rarely, an infection may develop following surgery.  If this occurs it will require a prolonged hospitalization with high doses of antibiotics. 

Acoustic Neuroma Association

The Acoustic Neuroma Association is an organization to provide support and information for patients who have acoustic neuromas and to provide support to patients with tumor related disabilities.

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