A vestibular schwannoma, or acoustic neuroma is a type of noncancerous tumor that presses against the nerves in a person’s inner ear. Its name derives from the fact that it results from an overgrowth of Schwann cells, which insulate the nerves in the ear. Though it can strike at any age, vestibular schwannomas usually affect people in middle age. The tumor impairs a person’s sense of balance and can cause hearing loss. A large vestibular schwannoma can press on the brain or the facial nerves.
Definition & Facts
There are two kinds of vestibular schwannomas. The first one, the unilateral acoustic neuroma, is found in only one ear and is the most common sort of schwannoma. The second type, the bilateral acoustic neuroma, is found in both ears. This is an inherited condition caused by a disease called neurofibromatosis type II, or NF2. About 1 in 100,000 people develop a vestibular schwannoma.
Symptoms & Complaints
They suffer headaches and mental confusion. There is numbness and tingling in the face, and in rare cases the facial nerve may be paralyzed. The symptoms of vestibular schwannoma resemble several other diseases of the inner ear such as Ménière's disease, so diagnosis can be difficult.
Scientists believe that vestibular schwannomas can happen when there is a mutation of a gene that is found on chromosome 22. This is true of both unilateral and bilateral vestibular schwannomas. People who have undergone radiation therapy around their neck or face are also at higher risk for vestibular schwannoma. Studies exploring the link between occupational noise exposure and the incidence of vestibular schwannomas have been inconclusive.
Diagnosis & Tests
First, the doctor examines the patient’s ears and gives them a hearing test, or audiometry. It is a common test where the patient is fitted withe earphones and listens to sounds and someone speaking. The earphones are connected to a machine that measures how well the patient responds to what they’re hearing.
Another diagnostic test is the brainstem auditory evoked response, or BAER. This measures how the patient’s brain waves react to different sounds. The patient also wears earphones during this test, and electrodes are attached to their scalp to monitor how the brain reacts to the sounds.
A magnetic resonance imaging (MRI) scan of the patient’s head helps find the tumor and reveal its size. MRIs use magnets and radio waves instead of radiation to look inside of the skull and generate very detailed, three-dimensional pictures of the tumor. The patient is first injected with a contrast dye. The vestibular schwannoma takes up more of this dye than the surrounding tissue, which allows it to be seen more clearly. It shows up as a patch of brightness within the patient’s ear.
Treatment & Therapy
The physician can opt to surgically remove the tumor, but sometimes it is so tiny that the doctor will take an approach of watchful waiting. This is most often done with older or very sick patients where the tumor isn’t expected to grow very much in the time they have left to live.
The larger the tumor is, the more difficult and dangerous it is to remove. Surgery on a large vestibular schwannoma puts the patient at risk for damage to their hearing, their facial nerves, and their balance. Nonetheless, there are several types of surgery that can be used to remove a large vestibular schwannoma. These surgeries are types of craniotomy, though they have different approaches.
One type of surgery is the keyhole brain surgery, or retrosigmoid craniotomy. In this surgery, the doctor makes an incision behind the ear to access the tumor. Keyhole brain surgery causes less pain, less scarring, and a faster recovery time for the patient.
In a translabyrinthine craniotomy, the surgeon also makes an incision behind the ear, but removes the mastoid bone and the semicircular canals of the ear to get access to the tumor. This operation is done when there is no longer hearing in the ear or the patient has agreed to have their hearing sacrificed. Removing the ear’s semicircular canals results in complete deafness in that ear, though the translabyrinthine craniotomy reduces the risk of damage to the patient’s facial nerve.
Large vestibular schwannomas can be treated with radiosurgery. This is a precise use of radiation to destroy an area of diseased tissue. Radiosurgery can be given in several small doses as opposed to one large dose. The smaller dose option, which is also called fractionated stereotactic radiosurgery, lets the doctor have more control of the procedure and seems better at preserving the patient’s hearing and the integrity of their facial nerve.
If patients suffer hearing loss after their vestibular schwannoma surgery, they can be helped with a BAHA, or bone-anchored hearing aid that the doctors implant beneath the skin around the ear. This device osseointegrates into the skull and helps transmit sound waves to the ear.
People who have suffered from bilateral acoustic neuroma can benefit from cochlear implants, which send sound waves directly to the hearing nerve, which then passes those sound waves to the hearing centers of the brain.
Sometimes, patients who have had surgery to remove a vestibular schwannoma suffer a leak of cerebrospinal fluid. This can happen when there’s a tear in the dura mater, the tough membrane (meninges) that protects the brain.
Prevention & Prophylaxis