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ACOUSTIC TUMOR
GENERAL COMMENTS
Acoustic tumors are fibrous growths originating from the balance
nerve and are not malignant. They do not spread to other parts
of the brain, other than by direct extension. They constitute
approximately 10% of all brain tumors. They are located between
the brain and the inner ear, adjacent to vital brain centers.
As they grow, they cause involvement of the surrounding nerves.
If they are allowed to grow over a long period time, they
press into the vital brain centers, and will eventually cause
pressure on the brain and ultimately this could be fatal.
In most cases, these tumors grow slowly. However, in other
people the growth is quite rapid and multiple symptoms may
develop. At times there may be bleeding into one of these
tumors causing sudden new symptoms. The cause of most acoustic
neuromas is unknown. There is a small group of patients who
have acoustic tumors as a result of having neurofibromatosis
Type II, which in genetically determined.
Acoustic tumors usually displace normal tissue as they grow,
yet remain within their lining (encapsulated). An acoustic
neuroma first distorts the eighth nerve, and then presses
on the seventh (facial) nerve. The slowly enlarging tumor
protrudes from the internal auditory canal and as mentioned
will ultimately press into the brainstem. The tumor also may
press on adjacent nerves, such as the fifth, or trigeminal
nerve, which is the nerve providing facial sensation. Pressure
on the brainstem, caused by tumor growth, can be life threatening.
Many diagnostic procedures are used to be as certain as possible
of an accurate diagnosis, and to determine the extent of the
tumor growth. When treating these tumors, the preservation
of life is the most important objective. When the tumors are
small, the morality rate (i.e., loss of life) is less than
1%. When they are middle or large sized, the mortality rate
is approximately 3%. The second objective of surgery is to
preserve as many vital structures as possible. In many cases,
a completely normal life results following surgery and in
others, minimum or even maximum degrees of handicap may result.
The first symptom from the tumor is usually some disturbance
in hearing, such as inability to hear on the telephone, fullness
in the ear, and/or tinnitus. This is due to pressure on the
cochlear portion of the eighth nerve but also due to involvement
of the blood supply to the hearing structure. The cochlear
nerve is more sensitive to pressure than most other cranial
nerves. The ability to hear requires not only an intact nerve
but adequate blood supply to the hearing structure. The blood
supply to the cochlear nerve and to the cells receiving the
sound in the ear comes from the internal auditory artery.
This artery originates inside the head and passes through
the internal auditory canal with the nerves, and therefore
is involved with the tumor. Sudden deterioration or fluctuation
in hearing may relate to pressure on this artery.
DIAGNOSIS OF ACOUSTIC NEUROMA
The diagnosis of an acoustic neuroma begins with a complete
history, physical examination, and conventional audiologic
evaluation. Following this, if there are any indications
of tumor, an auditory brainstem response (ABR) test maybe
done with a computerized audiometer. This uses a sophisticated
computerized audiometer to analyze the electrical activity
of the hearing nerves on both sides to determine if there
is normal conduction of the signals to the brain. If the conduction
is slowed down on one side, this may indicate a tumor. CAT
scanning or Magnetic Resonance Imaging (MRI) scans are sophisticated
imaging methods used to determine (by picture) the cerebellopontine
angle region of the brain to determine if there is an acoustic
neuroma present. At times, an electronystagmagram (test of
the balance system) may be used to determine the involvement
of the tumor with the balance nerves.
TREATMENT
At this time, the only treatment that can cure the patient
with an acoustic neuroma is surgical removal. The main goal
is the preservation of life, with a minimum of future physical
disturbances. To accomplish this, a team consisting of a Neurotologist,
Neurosurgeon, as well as an Internist, surgery as well as
the pre and post operative care. The Neurotologist and the
Neurosurgeon are co-surgeons during this surgical procedure.
Following surgery, the patient is usually admitted to the
intensive care unit for 24-48 hours post operatively for close
observation. After that period, the patient is transferred
to the floor or to an intermediate unit. Patients are usually
in the hospital for 7-10 days. Within the last several decades,
microsurgical techniques have been pioneered and refined.
With the use of an operating microscope and lasers, the Neurotologist
and Neurosurgeon are able to remove the tumor with an extremely
low mortality rate. Damage to the surrounding nerve tissue
is markedly decreased. Routinely facial nerve function is
monitored during surgery. In some situations the cochlear
nerve is also monitored when it appears feasible to preserve
hearing. The size of tumor, hearing status, patient's age,
and health determine which approach is utilized for removing
the tumor, when surgery is contemplated. When the tumor is
confined within the internal auditory canal, or just outside
the canal, and there is useful hearing, the middle fossa or
retrosigmoid approaches are generally preferred. Both approaches
allow the possibility of hearing preservation. When the hearing
is poor the translabyrinthine approach is preferred. The translabrythine
approach is very effective for tumor removal and preservation
of the facial nerve; however, there is no chance for hearing
preservation. For larger tumors occasionally the retrosigmoid
approach may be utilized, and occasionally a combined approach
such as middle fossa and retrosigmoid approach have been utilized
when one is trying to preserve hearing.
The treatment of vestibular schwanomas must be individualized
to each patient by an experienced team of doctors. Microsurgical
removal of these tumors remains the treatment of choice as
determined by the National Institute of Health (NIH) Consensus
Development Conference. Further research is needed on the
advantages and risks of other management options, which include
careful observation and stereotactic radiation.
The natural history of acoustic neuromas is not known. Each
tumor has its own biology and growth characteristics. In general,
acoustic neuromas are regarded to be slow growing averaging
2mm per year (range 1mm - 12mm/year). The critical question
to be answered when observation is considered is whether the
acoustic neuroma will cause any problems during the natural
course of the patient's remaining life span.
Another form of treatment which has recently developed is
the use of stereotactic radiation therapy (i.e., gamma knife).
Stereotactic radiation therapy is a technique based upon the
principle that a single high dose of radiation delivered precisely
to a small area of tumor could arrest the growth of the tumor
and not damage surrounding brain tissue and/or function. In
this technique, under a light general anesthesia, the head
is secured in a special device to hold it in a proper position
and a single dose of radiation is applied (stereotactically)
by the therapist. The dose is calculated to injury/kill tumor
cells yet minimize side effects or risks. There is no incision.
Almost all patients are discharged from the hospital the same
day or the following day. Life long follow up with MRI scans
is currently recommended. Unlike microsurgery which would
remove the tumor, stereotactic radiation therapy "controls"
the tumor growth. The tumor does not disappear but persists,
allegedly, in a "harmless" state. The risks of microsurgical
removal are well defined, short term and consistently quantified
in thousands of patients over 30 years. No such data exists
for acoustic neuroma treatment by stereotactic radiation therapy.
Short term risks of stereotatic radiation therapy appear comparable
to surgery in many areas. The real risk of stereotatic radiation
therapy may be ongoing, long term and, as yet, undetermined.
Tumor regrowth has been seen in 6 - 24% of stereotactic radiation
therapy patients. The long term growth control rates for stereotactic
radiation therapy have not been established. Serious complications
can also occur as a result of stereotactic radiation therapy.
Cost for microsurgery includes the operation, approximately
a seven day hospital stay, and a MRI scan at and three to
five years. The patient is also cured; disease free. Cost
for stereotactic radiation therapy includes the treatment
and MRI scans are required at 6, 12, 24, 48, 96, etc. months
as the tumor persists. There are medical costs associated
with this follow up. When the tumor regrows, the substantial
cost of salvage surgery must be factored. There is also evidence
that suggest salvage surgery in a patient who has had prior
stereotactic radiation therapy is much more difficult with
increased risk to facial nerve preservation. Radiation therapy
represents an alternative for patients who are elderly, or
have medical problems such as cardiac or pulmonary disease
and are at high risk for surgical removal.
SIZE OF TUMOR
Risks and complications of surgery vary with the size of the
tumor. Larger tumors have more serious complications, and
more likelihood of complications. In addition, the approach
to remove the tumor may differ, depending upon the size the
tumor, the patient's medical status, age of the patient, and
the status of the hearing. The removal of an acoustic tumor
is a major surgical procedure, entailing a craniotomy (opening
into the skull), with possibilities of serious complications,
even death, whether the tumor is large or small. Different
approaches are used as indicated above to minimize the complications
and, at the same time, remove the entire tumor. Tumors are
classified as small, medium, or large canal extending from
the inner ear toward the brain. Contained in this canal are
the hearing and balance nerves, as well as the facial nerve,
which enables the face to move on that side. In addition,
there are numerous blood vessels which supply the inner ear.
The operation for acoustic tumors is performed under general
anesthesia, using an operating microscopic. The surgical approach
to a small tumor may be the middle fossa approach, through
an incision in front of and above the ear; by the suboccipital
approach, with an incision toward the back of the head; or
a translabyrinthine approach may be used. The approach is
determined by the amount and quality of hearing in each patient.
In the vast majority of cases of small tumors, the tumor is
totally removed. Every effort is made to preserve the hearing
in small tumors by one of the first two approaches, and still
remove the tumor. However, it is imperative that tumor removal
take precedence over hearing preservation. In approximately
35% of the cases, serviceable hearing may be preserved. If
the tumor involves the hearing nerve, or an artery leading
to the inner ear, total loss of hearing will result in the
operated ear.
Medium Tumor
The treatment of vestibular schwanomas must be individualized
to each patient by an experienced team of doctors. Microsurgical
removal of these tumors remains the treatment of choice as
determined by the National Institute of Health (NIH) Consensus
Development Conference. Further research is needed on the
advantages and risks of other management options, which include
careful observation and stereotactic radiation.
In a medium tumor, this is an extension from the bony canal
towards the brain, but there is not yet pressure on the brain
itself.
Again, the surgery is performed under general anesthesia,
utilizing an operating microscope and surgical team. A translabyrinthine
approach is made through an incision behind the ear, over
the mastoid bone. The mastoid and inner ear structures are
removed to expose the tumor. The tumor is then totally removed,
in the vast majority of cases. The mastoid bone defect is
closed with fat taken from the abDombn. This approach sacrifices
the hearing and balance nerves in the operated ear, and the
patient is made permanently deaf on that side. This approach
has been developed to provide maximum safety to the facial
nerve, and allow complete removal of the tumor. The balance
mechanism of the opposite ear will provide stability for the
patient in approximately one to four months.
Large Tumor
The large acoustic tumor has extended out of the bony canal,
and into the brain cavity, producing pressure on the brain
and vital structures. The approach to a large acoustic tumor
requires more extensive removal of the bone, to expose the
tumor and control large vessels, which obstruct access to
the tumor. Occasionally special vascular studies are required
prior to surgery to help diagnose the location of larger vessels.
The surgical approach, the translabyrinthine-suboccipital
approach, is done through an incision behind the ear. The
mastoid bone, inner ear structures, and a portion of the skull
are removed to expose the tumor. The tumor is then totally
removed, unless vital sign changes prevent its removal from
the brainstem. If there are changes in blood pressure, pulse
rate, or respiratory rate, the surgery may have to be terminated
before the tumor is totally removed. In this instance, it
would be necessary to have a second operation to completely
remove the tumor. The surgical defect is closed with fat taken
from the abDombn. The translabyrinthine-suboccipital approach
causes the patient to be permanently deaf in the operated
ear. The balance mechanism is removed, but the balance mechanism
of the opposite ear will provide stabilization of the patient
in one to four months.
RISKS AND COMPLICATIONS OF ACOUSTIC TUMOR SURGERY
It is not possible to list every complication that may occur
before, during, and following a surgical procedure. The following
discussion is included to indicate some of the risks and complications
peculiar to cerebellopontine angle tumor surgery. In general,
the smaller the tumor at the time of surgery, the less risk
of complications. However, all these operations are major
and may have significant complications.
Hearing Loss
Occasionally in small tumors it is possible to remove the
tumor and preserve hearing: however, in the vast majority,
it is not. There must be good hearing and the tumor must be
located in a precise position to allow hearing preservation.
In the majority of the time, total hearing loss results in
the operated ear from the surgery. Fortunately, the development
of the CROS hearing aid has allowed the transfer of sound
from the operated ear to the other ear, so that one may hear
for social or business purposes from the operated side.
Ear Noises
Ear noise (tinnitus) usually remains the same after surgery
as it did before surgery. In approximately 30% of patients
the tinnitus may be less, but in 10% it may be more noticeable.
Taste Disturbance and Mouth Dryness
In approximately 5% of the patients, this disturbance may
be prolonged. But in most, it lasts for a few weeks and then
disappears.
Dizziness and Balance Disturbance
In the vast majority of cases of acoustic tumors, it is necessary
to remove the balance nerve to remove the tumor. However,
in many cases the balance nerve has been damaged by the tumor
prior to surgery and is causing unsteadiness. In many of these
patients, there is an improvement in the preoperative unsteadiness.
Nevertheless, in most patients there is some temporary dizziness
following surgery, which may be severe for days to a few weeks.
Imbalance or unsteadiness on head motion is prolonged in 30%
of the patients. Some patients notice unsteadiness when fatigued
for several years. There are programs to enable the patient
to overcome the dizziness and imbalance. In a few cases, the
blood supply to the portion of the brain responsible for coordination
(the cerebellum or brainstem) is decreased by the tumor or
removal of the tumor. Difficulty in coordination and balance
may, therefore, last in these patients for years.
Although acoustic tumors do not arise from the facial nerve,
they are in intimate contact with it. This nerve controls
the movement of the muscles to the face, including those that
close the eye. It is very common to have a temporary paralysis
of the muscles of the face following the removal of acoustic
tumors. This weakness may persist for six to twelve months
and occasionally, there may be permanent residual weakness
or paralysis.
A facial paralysis may result from nerve swelling, or nerve
damage. If it is merely nerve swelling, it may return in a
short time (three weeks to three months). Swelling of the
nerve is common due to the fact that the nerve is compressed
and distorted by the tumor in the internal auditory canal.
Tumor removal with the use of the operating microscope usually
results in preservation of the nerve, but nerve stretching
may result in swelling of the nerve, with subsequent temporary
paralysis. Facial function is observed for approximately one
year following surgery. If it becomes certain the facial function
will not recover (approximately 15% of the cases), a second
operation may be performed to connect the facial nerve to
a nerve in the neck (facial-hypoglossal anastomosis).
Eye Complications
The major medical problem with facial paralysis following
this surgery is that the eye may become dry and unprotected.
It can then become infected or abraded. Care by an eye specialist
(ophthalmogist) may be necessary. It may be necessary to use
ophthalmic (eye) drops, or apply ointment to the eye frequently,
insert a gold weight beneath skin in the upper eye lid to
close the eye lids, or even to partially sew the eyelids closed.
The purpose of these efforts is to keep the eye moistened,
as well as provide comfort, and improve the appearance.
Other Nerve Weaknesses
Acoustic tumors may become involved with other nerves besides
the hearing and balance nerves, and the facial nerve. They
may be in contact with nerves which supply the eye muscles,
mouth, neck and throat. These nerves may be injured with resultant
double vision, numbness of the throat, and tongue, weakness
of the shoulder, weakness of the voice and difficulty swallowing.
In some cases these problems are permanent.
Brain Complications and Death
These tumors, as they grow, press on vital brain centers which
control breathing, blood vessel and heart function. As the
tumor enlarges it may begin to receive blood supply from the
brain centers. Usually careful dissection under the microscope
avoids complications. However, the blood supply to the vital
brain centers may be disturbed in the removal of the tumor.
If this occurs, serious complications result, including loss
of muscle control, stroke, paralysis, or death. In our experience,
death occurs rarely as the result of small tumors, less than
3% of medium sized tumors, and in about 5% of the large tumors.
Postoperative Spinal Fluid Leak
In all cases of acoustic tumor surgery, there is a temporary
leak of cerebrospinal fluid (fluid surrounding the brain).
This leak is closed prior to completion of surgery with fat
from the abDombn. However, approximately 5% to 10% of the
time this leak reopens and further surgery may be necessary
to close it. Most of the time, this leak can be closed by
placing a drain in the cerebrospinal fluid space through the
back. While this drain is in place the patient has to remain
in bed, but in the vast majority of cases this stops the leak
without further surgery.
Postoperative Bleeding and Brain Swelling
Brain swelling and bleeding may develop after tumor surgery.
If this occur, a subsequent operation may be necessary to
open the wound, stop the bleeding, and allow the brain to
expand. If the brain swelling is severe, it often results
in paralysis or death.
Postoperative Infection
Postoperative meningitis occurs in approximately 3% of the
patients. Meningitis is an infection of the fluid and covering
surrounding the brain. In a very small percentage of cases,
an infection may involve only the external portion of the
wound. When these complications occur, hospitalization is
prolonged, and treatment with high doses of intravenous antibiotics
is indicated. Occasionally, these antibiotics may cause an
allergic reaction, suppress the body's blood forming tissues,
or may produce hearing loss in the good ear. Fortunately,
antibiotic complications are rare.
Transfusion Reaction
Rarely, it is necessary to administer a blood transfusion
during surgery. Adverse reactions to transfusions are rare.
An occasional late complication is a viral infection of the
liver (hepatitis). An even more rare complication is AIDS.
Recent innovations in blood banking, however, have made this
an extremely rare complication. Blood transfusions, currently,
are not given unless there is bleeding of over two units of
blood. It is possible and advisable to donate blood for yourself
or have suitable family members donate blood for you. This
must be done in advance of surgery by at least two weeks.
PARTIAL VS. TOTAL REMOVAL OF ACOUSTIC TUMORS
The goal of acoustic tumor surgery is to remove the entire
tumor and preserve as much function as possible. Partial tumor
removal may be necessary if the patient's response to surgery
indicates disturbances of any vital brain centers, such as
respiration, blood pressure, or heart function. Most of the
time, if there is a disturbance in the brain center and surgery
is stopped, function can be restored. Occasionally, however,
once the vital brain centers are disturbed, they do not recover.
If termination of the operation is necessary without removal
of the entire tumor, the remaining portion of the tumor may
gradually enlarge to again produce symptoms. A subsequent
operation can often then be accomplished without a significant
change in vital signs, as there is a change in the relationship
of the tumor to the brain.
If the tumor is partially removed, you will be so informed.
As mentioned above, reduction of the size of the tumor often
allows it to separate from the vital brain centers, and it
can be removed at a later date. In most cases a wait of two
weeks to four months is indicated, depending upon the circumstances.
In other cases, the course of continued observation is determined
best for the patients. If this is necessary, x-ray imaging
techniques will be used to evaluate the tumor from time to
time for possible regrowth.
CONCLUDING REMARKS
There is no known "cure" for an acoustic neuroma,
except surgical removal, at the present time. The earlier
tumors are diagnosed and removed, the less likely the possibility
of serious complications.
It is important to face the problem of an acoustic neuroma
as it exists at the time of diagnosis, and accept whatever
risks are necessary to remove the tumor. Maintaining a positive
attitude before, during, and after the surgery is necessary
for all members of the team, as well as the patient, for the
best results.
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