What is a vestibular schwannoma (acoustic neuroma)?
A vestibular schwannoma (also known as
acoustic neuroma, acoustic neurinoma, acoustic schwannoma, or acoustic
neurilemoma) is a benign, slow-growing tumor that develops from the nerves that
control balance and hearing. Approximately one out of every 100,000 individuals
per year develops a vestibular schwannoma.
The tumor arises from an overproduction of
Schwann cells—the cells that normally wrap around the nerves to help support and
insulate nerves and transmit impulses. As the tumor grows, it affects the
hearing and balance nerves, usually causing hearing loss on that side, tinnitus
(ringing in the ear), and imbalance while walking. As the tumor grows, it can
interfere with the sensations over the face (the trigeminal nerve), causing
facial numbness. Vestibular schwannomas can also affect 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), which could be
life-threatening.
How
is a vestibular schwannoma diagnosed?
One sided hearing loss and/or tinnitus and
loss of balance/dizziness are early signs of a vestibular schwannoma.
Unfortunately, early detection of the tumor is sometimes difficult because the
symptoms may be subtle and may be ignored in the early stages of growth. Also,
these symptoms are commonly encountered in many middle and inner ear problems.
Once the symptoms appear, a thorough ear examination and hearing and balance
testing (audiogram) are essential for proper diagnosis. Magnetic resonance
imaging (MRI) scans are critical in the early detection of a vestibular
schwannoma and are helpful in determining the location and size of a tumor and
in planning its treatment.
How
is a vestibular schwannoma treated?
There are three options for managing a
vestibular schwannoma:
(1) surgical removal,
(2) radiation, and
(3) observation.
Sometimes, the tumor is surgically removed
(excised). 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 small, hearing
may be saved and accompanying symptoms may improve by removing it to prevent
its eventual effect on the hearing nerve. As the tumor grows larger, surgical
removal is more complicated because the tumor may have damaged the nerves that
control facial movement, hearing, and balance and may also have affected other
nerves and structures of the brain.
The removal of tumors affecting the
hearing, balance, or facial nerves can sometimes make the patient’s symptoms
worse because these nerves may be injured during tumor removal.
As an alternative to conventional surgical
techniques, radiosurgery (that is, radiation therapy—the “gamma knife” or LINAC
based Stereotactic Radiotherapy) may be used to reduce the size or limit the
growth of the tumor. Radiation therapy is sometimes the preferred option for
elderly patients, patients in poor medical health, patients with bilateral
vestibular schwannoma (tumor affecting both ears), or patients whose tumor is
affecting their only hearing ear. When the tumor is small and not growing, it
may be reasonable to “observe” the tumor for growth with periodic MRI scans.
Bilateral vestibular schwannomas affect
both hearing nerves and are usually associated with a genetic disorder called
neurofibromatosis type 2 (NF2). Half of affected individuals have inherited the
disorder from an affected parent and half seem to have a mutation for the first
time in their family. Each child of an affected parent has a 50 percent chance
of inheriting the disorder. 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 other nerves in
the brain or elsewhere in the body.
What
is the outcome of patients treated for vestibular schwannoma?
Most patients with vestibular schwannoma
that undergo treatment (surgery or radiosurgery) go on to lead a normal healthy
life with or without some morbidity pertaining to facial nerve function. The
outcome following successful vestibular schwannoma surgery is extremely good.
