Brain Tumors

What is an acoustic neuroma?

Acoustic Neuromas are benign, usually slow growing tumors that arise from the balance or hearing nerve (eighth cranial nerve) and do not spread to other parts of the body. They make up 6-10% of all brain tumors and there are approximately 2280 new cases per year in the United States.

What causes it to grow?

The cells which form an acoustic neuroma are called schwann cells and make up the lining of the eighth cranial nerve as it passes through a canal which connects the inner ear to the brain. What causes these cells to reproduce rapidly is unknown. As they multiply, they form a small tumor which can fill the canal.

What are the signs and symptoms of an acoustic neuroma?

They include unilateral hearing loss, tinnitus or ringing in the ear, and balance problems. As they get larger they can produce other symptoms including headaches, unilateral facial numbness and tingling, unilateral facial weakness and fullness in the ear.

What damage can it cause if untreated?

As the tumor grows, it can cause permanent unilateral hearing loss or facial paralysis. The tumor can extend into the brain putting pressure on a vital brain structure called the brain stem. If allowed to continue to grow over a long period of time, this pressure on the brain can be ultimately fatal. Because these are usually very slow growing tumors, fortunately, this rarely occurs.

How is it found?

The diagnosis of AN is made after performing many tests. They include:
A. Audiogram - a hearing test demonstrates unilateral hearing loss and poor speech discrimination.
B. Brainstem auditory evoked response (BAER)- predicts potential for salvaging hearing postoperatively.
C. Electronystagmography (ENG).
D. CT and MRI scans with contrast demonstrate the tumors, make the final diagnosis.

What are my treatment options?

A. Do nothing.

This option is typically reserved for patients who:
1) Refuse any treatment
2) Have a very small tumor and are without many signs or symptoms.
3) Are elderly with many medical complications and have a small or medium sized tumor.
These patients need to understand that with time, the tumor will probably take the hearing in their affected ear. Periodic MRI scans are performed to follow the size of the tumor.

B. Surgery

Is the best treatment option for most patients because it is the only option that has an excellent chance of curing the lesion.

C. Gamma Knife (Radiation Treatment)

This treatment option is typically reserved for patients who:
1) Have residual tumor after a craniotomy.
2) Are elderly.
3) Have multiple medical problems making surgery too risky.
4) Must have a tumor <3 cm. in size.

The goals of the gk treatment are to prevent the tumor from getting any larger. This occurs in 85% of the patients. The tumor may shrink in size but usually does not disappear.

The risks of gamma knife treatment for AN include:
1) Delayed temporary or permanent facial weakness
2) delayed temporary or permanent hearing loss in the affected ear.
3) possible surrounding brain damage from the radiation.

What are the different surgical approaches and how does the surgeon decide on which one would be best for me?

The choice of which approach to use is very patient specific. It depends on location and size of the tumor, level of residual hearing, results of the speech discrimination and Baer tests, patients goals, and the surgeon's operating preference.

It is possible to save hearing only in a minority of cases. If hearing preservation is successful, the preserved hearing is not better that the preoperative level and most of the time is a little worse. The larger the tumor, the lower the chances for hearing preservation. In some cases with poor preoperative hearing or a large tumor, it is better to sacrifice the hearing in order to remove the whole tumor.

The surgical approaches include:
1) Translabyrinthine
With this approach, the hearing and balance mechanism of the inner ear are sacrificed. Therefore, the affected ear is made permanently deaf and your balance may be "off" for approximately 1-4 months. This is the amount of time it typically takes for the balance mechanism in the opposite ear to take over. This approach is typically reserved for patients who have a large tumor and/or have poor hearing in their affected ear.

Benefits:
(a) best if able to remove the whole tumor.
(b) best if able to preserve the facial nerve.
Downfalls:
(a) permanent hearing loss in the affected ear.
(b) may have temporary imbalance.
(c) possibly higher rate of cerebrospinal fluid csf leak.
(d) with this approach you will have some fat taken from your abdomen to close the surgical defect.

(2) Middle Fossa or Retrosigmoid
With these approaches, every effort is made to preserve the hearing and still remove the tumor. In about 50% of the cases, the tumor involves the hearing nerve or artery leading to the inner ear and total loss of hearing results. This approach is typically reserved for patients who have a small tumor and who have good hearing and speech discrimination in their affected ear.

Benefits:
(a) attempt at preserving pre-op hearing level.

Downfalls:
(a) may not be able to remove the whole tumor.
(b) 50% of the time will not be able to preserve hearing.
(c) more of a chance of potentially harming the facial nerve.
(d) risk of csf leak.

(3) Suboccipital

For larger tumors where hearing is thought to be preservable.

Benefits:
(a) chance of preserving hearing especially in cases of small tumors.
(b) equivalent rate of facial nerve preservation.

Downfalls:
(a) increased risk of leaving residual tumor.
(b) possibly more post op headaches.

What if the whole tumor cannot be removed?

The goal of the management of acoustic neuromas is total removal of the tumor without complications. Premature termination of the operation may be necessary based on the surgeon's judgment because of intraoperative signs of vital brain center disturbance or significant swelling of the brain. If this occurs, you will be informed by your surgeon as to approximately how much of the tumor remains. Options at this point include repeat surgery at a later date, gamma knife, or to follow tumor size with MRI scans. Your surgeon will discuss risks and benefits of all of these options specific to your case.

Who are the members of the surgical team?

The team is made up of a neurosurgeon (brain surgeon), an otolaryngologist (ear surgeon), two neurosurgery residents, two otolaryngology residents, a neurosurgical physician assistant and a neurosurgical nurse coordinator.

What are the risks and complications of acoustic neuroma surgery?

A. Hearing Loss
In small tumors it is sometimes possible to save the hearing by removing the tumor. In large tumors or with the translabyrinthine approach, hearing is lost in the affected ear only.

B. Tinnitus (ringing in the ear)
Tinnitus in the affected ear may be the same or worse postoperatively. Very rarely is it improved after surgery.

C. Dizziness and balance disturbance
During surgery it is necessary to remove part or all of the balance nerve and, in the translabyrinthine approach to remove the inner ear balance mechanism . Because the tumor usually damages the balance system, tumor removal sometimes can result in improvement in any preoperative unsteadiness. Dizziness is common following surgery and may be severe for a few days. Imbalance or unsteadiness on head motion is prolonged until the normal balance mechanism in the opposite ear compensates for the loss in the operated ear. This usually takes one to four months. A few patients notice unsteadiness for several years, especially when they are fatigued.

D. Facial paralysis
Acoustic tumors are in intimate contact with the facial nerve which closes the eye and controls the muscles of facial expression. Temporary paralysis of the facial nerve is common following removal of an acoustic tumor and usually results from nerve swelling or damage. Careful tumor removal with the help of an operating microscope and a facial nerve monitor, usually results in the preservation of the nerve. But nerve stretching may result in swelling of the nerve, which may cause temporary paralysis. Facial weakness may persist for 6-24 months. A few patients experience permanent residual weakness or complete paralysis. With patients who experience complete paralysis, occasionally a facial nerve graft can be performed in attempt to recover some facial nerve function.

E. Postoperative cerebrospinal fluid (csf) leak
Acoustic tumor surgery results in temporary leak of cerebrospinal fluid. This leak is closed prior to the completion of surgery with fat removed from the abdomen. Occasionally this leak reopens with fluid leaking either from the nose or out of the wound. Repair of this leak is achieved by either a pressure dressing, a lumbar drain (a drainage of csf from the low back region) placement, or further surgery.

F. Other risks and complications
These include eye complications only if facial paralysis is present, taste disturbance, mouth dryness, other cranial nerve weakness, post-operative headache, brain swelling, post-operative bleeding, post-operative infection, blood transfusion reaction, other medical complications, and death. Fortunately, these complications are extremely rare (they occur less than 3% of the time).

Your neurosurgeon or neurosurgical physican assistant would be more than happy to discuss the risk percentages specific to your situation.

For further information or to schedule an appointment please contact the Neurosurgery Clinical Office at (323) 442-5720