Acoustic Neuroma( Vestibular Schwannoma ) Acoustic neuroma is a benign tumor that grows in the internal auditory canal and affects the hearing, facial, and balance nerves.
Outcomes for Acoustic Neuroma
What are the consequences of losing hearing in one ear?
When you are unable to hear from one ear, the ability to localize sounds or tell where a sound is coming from is lost. It is the minute time difference between when a sound enters one ear and the other that allows the brain to perceive the direction from which the sound is originating.
There are certain types of hearing aids called CROS and BICROS aids that are helpful when hearing is lost in one ear. These hearing aids take sound that normally would have entered the non-hearing ear and re-route the signal to the hearing ear. It involves wearing at least an ear mold in both ears.
The BAHA implant works especially well in patients with single-sided deafness.
What are the chances of saving hearing?
In the best of circumstances, when there is hearing present, when waveforms are present on the auditory brainstem response, and when there is a small tumor involving the internal auditory canal, the chances of preserving any hearing are about 70% with the middle fossa approach. In all other situations, the chances of hearing preservation are lower.
What happens to tinnitus?
It is attractive to believe that an acoustic neuroma involving the vestibular nerves and the cochlear nerve might be causing the tinnitus that many patients experience as an initial symptom. After an acoustic neuroma is removed and even when the cochlear nerve has been removed, tinnitus may persist. We now believe that the presence of an acoustic neuroma may permanently sensitize nerve cells or neurons along the auditory pathway within the brainstem.
For more information about treatment of tinnitus, refer to Tinnitus.
Of note, we have not had any patients with worsening tinnitus following surgery.
What will happen to the balance function?
When an acoustic neuroma is excised, the superior and inferior vestibular nerves are usually removed. The balance information that was being transmitted from the inner ear to the brainstem comes to an immediate stop. Consequently, it is not unusual after surgery for patients to experience some disequilibrium.
The degree of disequilibrium experienced depends on how much balance information was reaching the brainstem prior to surgery. If the tumor had destroyed the vestibular nerves so that no balance information was reaching the brainstem, then the brain will have already compensated for the lack of balance information from that inner ear. In this case, the patient will not experience any disequilibrium after the operation. If the tumor only partially destroyed the vestibular nerves so that some information was still reaching the brainstem, then the brain will have only partially compensated. In this case, the patient will experience some disequilibrium after the operation.
Following surgery, the brain needs time to compensate for and adapt to the lack of balance information it is getting from the operated ear. The time this adaptation takes is variable and generally unpredictable. It is generally assumed that older patients take longer to compensate than their younger counterparts. Patients experience the most disequilibrium immediately after the operation. Usually 2-3 days after the operation, they are able to walk with some assistance. Approximately 1-2 weeks after the operation, head motions may trigger transient disequilibrium. Several months after the operation, only the most sudden head motion may lead to momentary disequilibrium. About six months after surgery, this momentary disturbance usually resolves.
Vestibular rehabilitation is an integral part of treatment of balance dysfunction. Our vestibular physical therapist, Dr. Stacey Buckner, PT, DPT, has an individualized program for patients with vestibular dysfunction. For more information, visit Balance Center of Maryland.
Facial nerve function following acoustic neuroma surgery
As mentioned previously, acoustic neuromas are benign tumors that arise from the vestibular nerves and may secondarily invade the cochlear nerve and impair hearing. These tumors usually push the facial nerve aside.
In most instances, the tumor can usually be dissected off the facial nerve. In these cases, some facial weakness seen soon after surgery will usually return to normal with time. The degree of facial nerve dysfunction after surgery cannot be reliably predicted. Generally, the larger the tumor is, the greater the chance of facial nerve dysfunction after surgery. On occasion, the tumor can be found to invade the facial nerve. If this is found, my preference has been to leave a small fragment of tumor on the facial nerve. I have not seen growth of these small fragments left on the nerve over time. Perhaps this is because most of the blood supply to the tumor has been lost.
On rare occasions with large tumors, the facial nerve can become disrupted during the course of tumor dissection. The facial nerve can be repaired at the time of surgery, in which case facial nerve recovery would begin 18 months following surgery. Another option is to divert some of the nerve fibers headed for the tongue toward the facial nerve in a separate operation.
It is very important to prevent dryness of the eye. With facial nerve weakness, it might be difficult to completely close the eye, leaving the cornea exposed. A feeling as though there is a particle of sand in the eye or redness of the conjunctiva indicates that the cornea is drying. Frequent use of artificial teardrops is a necessity. Lacrilube ointment can be used at nighttime. Occasionally, it becomes necessary to implant a small gold weight in the upper eyelid. The weight is heavy enough to allow the eye to close completely but light enough to be able to open the eye and have useful vision. The gold weight can always be removed later once facial nerve recovery occurs.
The role of facial nerve rehabilitation involving exercises and electrical stimulation is controversial. The true efficacy has yet to be determined.
Spinal fluid leakage following surgery
An uncommon complication of acoustic neuroma surgery is leakage of spinal fluid.
In all three approaches, spinal fluid can leak through the wound. This can usually be managed by placing another stitch under local anesthesia directly at the site of leakage.
Spinal fluid leaks from the nose
Spinal fluid may also enter the middle ear and drain down the Eustachian tube and out the nose. When this occurs, a pressure dressing with a lumbar drain is used for several days. The lumbar drain is placed in the back similar to a spinal tap; however, here, a small plastic tube is left in place. Spinal fluid is drawn out periodically over several days, and then the drain is removed. This causes lowered pressure in the spinal fluid space, which allows time for healing at the operative site. On rare occasion, exploration of the wound may become necessary to close the site of leakage.