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Disorders
We Treat
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Vestibular Schwannoma
(Acoustic Neuroma)
A vestibular schwannoma (also known as acoustic neuroma) is a benign,
usually slow-growing tumor that develops from the balance and hearing
nerves supplying the inner ear. The tumor comes from an overproduction
of Schwann cells--the cells that normally wrap around nerve fibers like
onion skin to help support and insulate nerves. As the vestibular schwannoma
grows, it presses against the hearing and balance nerves, usually causing
unilateral (one-sided) or asymmetric hearing loss, tinnitus (ringing in
the ear), and dizziness/loss of balance.As the tumor grows, it can interfere
with the face sensation nerve (the trigeminal nerve), causing facial numbness.
Vestibular schwannomas can also press on the facial nerve (for the muscles
of the face) causing facial weakness or paralysis on the side of the tumor.
If the tumor becomes large, it will eventually press against nearby brain
structures (such as the brainstem and the cerebellum), becoming life-threatening. |
What is the difference
between unilateral and bilateral vestibular schwannomas?
Unilateral vestibular schwannomas affect only one ear. They account for
approximately 8 percent of all tumors inside the skull; one out of every
100,000 individuals per year develops a vestibular schwannoma. Symptoms
may develop at any age but usually occur between the ages of 30 and 60
years. Unilateral vestibular schwannomas are not hereditary.
Bilateral vestibular schwannomas affect
both ears and are hereditary (inherited from one's parents). Bilateral
vestibular schwannomas occur in individuals with a genetic disorder known
as neurofibromatosis--type 2 (NF2). Affected individuals have a 50 percent
chance of passing this disorder on to their children. Unlike those with
a unilateral vestibular schwannoma, individuals with NF2 usually develop
symptoms in their teens or early adulthood. In addition, patients with
NF2 usually develop multiple brain and spinal cord related tumors. They
also can develop tumors of the nerves important for swallowing, speech,
eye and facial movement, and facial sensation. Determining the best management
of the vestibular schwannomas as well as the additional nerve, brain,
and spinal cord tumors is more complicated than deciding how to treat
a unilateral vestibular schwannoma. Further research is needed to determine
the best treatment for individuals with NF2.
Diagnosis: Early diagnosis of a vestibular
schwannoma is key to preventing its serious consequences. In more than
70% of the patients with vestibular schwannomas, hearing loss is the first
symptom. In most patients there is a gradual decrease in hearing with
difficulty in understanding spoken words often encountered. Ringing in
the ears, dizziness, vertigo and headache are less common symptoms. The
ringing or "tinnitus" may be constant or change with activity
such as exercise. In patients with very large tumors additional symptoms
may include weakness of facial muscles, double vision, hoarseness, facial
pain or numbness or difficulty swallowing.
Hearing loss
is shown in over 90% of patients the first time medical attention is sought.
The audiogram is important to determine the speech reception threshold
(SRT), speech discrimination (SD) and pure tone average (PTA). The
pattern of hearing loss may suggest nerve injury and include high frequency
hearing loss in excess of low frequency loss.
The appearance
of the vestibular schwannoma on the MRI is a rounded, enhancing mass with
extra-canalicular (outside the internal auditory canal of the skull) or
intra-canalicular or both components. Cysts may commonly be present within
the acoustic neuroma.
The diagnosis
is confirmed with a high degree of accuracy by the characteristic appearance
on MRI. As misdiagnosis is rare, confirmation by biopsy is not generally
needed.
Treatment:
There are three options for managing a vestibular schwannoma: 1. surgical
removal; 2. fractionated Stereotactic radiosurgery; 3. monitoring without
treatment.
Surgery:
The exact type of operation done depends on the size of the tumor and
the level of hearing in the affected ear. If the tumor is very small,
hearing may be saved. As the tumor grows larger, surgical removal
is more complicated because the tumor may have thinned-out the nerves
that control facial movement, hearing, and balance and may also have affected
other nerves and structures of the brain.
Surgery offers
immediacy but with higher up-front risk. The recurrence rate after surgery
is low, less than 5% confirmed with decades of follow-up. The risks of
surgery, however, include cerebrospinal fluid leak (5% to 17% risk), meningitis,
hydrocephalus and wound infection. Other common effects include a period
of headaches or balance difficulties. Other potential risks of surgery
include facial weakness. This risk increases with size of the tumor and
may range from 1% to 5% up to approximately 30% depending upon the size
(higher with larger size) and surgical procedure utilized.
Three surgical
approaches are commonly utilized. When there is a desire to attempt
to preserve useful hearing, the retrosigmoid or middle cranial fossa approaches
are often utilized. With these approaches hearing may be preserved
for a substantial proportion of patients (especially with smaller tumors)
but hearing loss remains a significant risk. When there is no useful
hearing or hearing is to be sacrificed, the translabyrinthine approach
is often considered. Although hearing is lost with the latter operation,
the risk of facial nerve injury may be reduced. The relative merits
of each of these approaches depends upon the individual anatomy, size
and location of tumor, presence of useful hearing, and individual patient
concerns about the particular risks of each approach.
Radiosurgery
offers effective treatment but takes longer to work when compared to surgery.
The risks of radiosurgery are also less than for surgery, and this is
the primary advantage of this approach. Radiosurgery can be given either
in a single session or in multiple sessions in which smaller daily doses
are given (fractionated stereotactic radiosurgery (FSR)). For single session
radiosurgery, the frame is "bolted" to the head, a scan is taken
and the radiation is given in one large "shot." For the FSR,
the patient has fitting of a special plastic mask that does not involve
incisions, drugs or hospitalization. A scan is taken, and the patient
then receives several smaller treatments, one per day. FSR is used
with the goal of further decreasing risks to nearby normal structures
and nerves as normal tissues are better able to resist fractionated radiotherapy
than tumor. With radiosurgery the tumor control rate is greater than
95% with maximum follow-up of 10-15 years.
Although
single shot Gamma Knife therapy is also offered at Johns Hopkins, we recommend
FSR for most patients. At Johns Hopkins, patients with neuromas smaller
than 3 cm will generally receive 5 treatments of FSR. Each treatment
lasts approximately 10 minutes. The acute side effects are minimal and
most patients can continue normal activity. In the months after treatment,
radiation related side effects may occur to a minority of patients, most
often headache, fullness of the ear, or decreased balance. These
effects, if they occur, are usually modest and resolve over a period of
months. There is a very high rate of facial nerve preservation with FSR. The
majority patients with good hearing will retain useful hearing in the
treated ear, but hearing loss is the most common permanent side effect. The
results of FSR at Johns Hopkins are summarized below.
Observation: As
acoustic neuroma may be slow growing, observation with delayed treatment
may be acceptable for some patients. This is especially the case
for elderly or infirm patients with mild symptoms where the risks of therapy
may be greater and where the tumor may not grow during their lifespan. Those
with smaller tumors may also decide upon watchful waiting, getting frequent
MRI’s and audiograms. In this situation it is highly likely that
treatment would eventually be needed, but there is potential to postpone
therapy for many years. Treatment would proceed when growth is confirmed
or symptoms worsen. For an individual considering this approach,
the risks of tumor growth causing symptoms or making later treatment more
difficult should be compared with the potential benefits of delaying treatment
along with its risks and side effects. Lifelong MRI and audiogram
follow-up are needed so that treatment might be given if the tumor grows.
Choosing
among the options:
Microsurgery
and radiosurgery are appropriate choices for the majority of patients,
and the decision must be quite individualized. We recommend consultation
both with specialists in microsurgery and radiosurgery prior to deciding
upon a treatment course.
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