An acoustic neuroma is a noncancerous or benign tumor that affects the nerves running from the inner ear to the brain.
In the later stages, an acoustic neuroma may affect the nerves of the cerebellum and brainstem and can increase pressure in the brain. These effects can be life-threatening. The tumor does not spread to other parts of the body, however.
Other names for acoustic neuroma are acoustic neurinoma, vestibular schwannoma, and auditory nerve tumor.
A layer of cells that doctors call Schwann cells covers nearly all healthy nerves in the body. Schwann cells provide insulation and support for nerve impulses. If they begin to multiply too quickly around the eighth cranial nerve, acoustic neuroma occurs.
The tumor usually grows slowly, over a number of years, but eventually, several symptoms may appear suddenly.
Acoustic neuroma is rare. According to the National Organization of Rare Diseases (NORD), it affects around 1 in every 100,000 people. There are around 2,500 new diagnoses each year in the United States, and it usually appears between the ages of 30 and 60 years.
Treatment depends on several factors, including:
- age of the affected individual
- general health of the person
- location and tumor size
In some cases, a doctor will recommend watchful waiting. If the tumor is small or slow-growing, no further action may be necessary.
If treatment is necessary, there are several options, as we describe here.
This is a type of radiation therapy that targets the tumor with radiation in a precise way. Doctors also call it the "gamma knife," and they consider it is a noninvasive treatment.
A doctor uses local anesthesia to numb the scalp and then attaches a lightweight head frame.
Imaging scans identify the location of the tumor and show the doctor where to apply the radiation beams.
The individual may need treatment over several sessions. It can also take weeks, months, or years to experience the effects of the treatment, and sometimes the tumor will return.
Radiosurgery is usually an option only if the tumor is 3 centimeters (cm) or less across.
This method allows a surgeon to remove all or part of the tumor through an incision in the skull, under general anesthesia, using special tools.
Sometimes, surgeons can only remove part of the tumor because removing all of it might cause damage to facial nerves. Damaging the facial nerves could lead to paralysis in the face.
A doctor may use radiosurgery to reduce the size or limit the growth of the tumor or to remove any remaining traces of the tumor after microsurgery. Carefully targeting the radiation enables the doctor to minimize damage to healthy tissue around the tumor.
After surgery, a doctor will monitor the person's recovery and check for recurrence of symptoms.
Sometimes, there is a high risk of hearing loss after surgery, especially if the person has a tumor on each acoustic nerve. In this case, the doctor may suggest delaying surgery for as long as possible.
Other side effects of treatment may include:
- facial weakness or numbness
- reduction in mental alertness if blood clots or a blockage of cerebrospinal fluid occur
- possible eye problems, including double vision or a drooping eyelid if treatment interferes with nerves
Researchers are currently looking into the following as possible future treatments aids:
- a role for aspirin in limiting tumor growth
- the use of new drugs to inhibit the cell mechanisms that cause the tumor to develop
Symptoms of an acoustic neuroma include:
- hearing loss in one ear in 90 percent of people with acoustic neuroma
- tinnitus, or ringing in the ears
- dizziness, loss of balance, and vertigo if the tumor affects the inner ear
- loss of sensation, sometimes affecting one side of the face and mouth
- loss of the sense of taste on the back half of the tongue
Headaches, vomiting, and altered consciousness can occur if a large tumor puts pressure on the brain. Vision problems can sometimes arise.
Acoustic neuroma is a slow-growing tumor, but it can push against vital brain structures and become life-threatening if not treated.
Acoustic neuroma size grading
An acoustic neuroma is:
- Small — when under 2 cm in size
- Medium — when 2 to 4 cm
- Large — when 4 cm or more
Precisely what causes Schwann cells to multiply and lead to an acoustic neuroma remains unclear. In most cases, there is no identifiable cause. However, there may be some risk factors, including:
Age: Acoustic neuroma tend to appear between the ages of 30 to 60 years
Family history: Neurofibromatosis type 2 can run in families. However, this accounts for only 5 percent of cases.
Radiation exposure: Significant exposure to radiation to the head and neck during childhood may increase the risk later in life.
Studies have suggested that some cases may be related to long-term exposure to loud noise. People have also speculated that cell phone use may contribute to the development of an acoustic neuroma, but research does not support this.
Neurofibromatosis type 2
People with NF2 usually have other tumors that affect the spinal cord and brain, and these can interfere with multiple nerves and body functions.
A doctor will carry out an examination and ask the person about their symptoms.
If they suspect an acoustic neuroma, they will probably request an MRI scan of the head. This imaging process will show if a tumor is present, where it is, and how big.
To rule out other causes of dizziness, hearing loss, or vertigo, the individual may undergo a hearing test, a balance test, and a test for brainstem function.
Other conditions with similar symptoms include:
- meningioma, a tumor that develops on the brain lining
- Meniere's disease
- neuritis, an inflammation of the nerves
- atherosclerosis, when the blood vessels narrow
Several complications can arise, including:
- Hearing loss: This may persist even after treatment.
- Dizziness and loss of balance: If this occurs, it can make daily activities difficult to do.
- Facial palsy: If surgery, or rarely, the tumor itself, affects the facial nerve, which is close to the acoustic nerve, the face may droop on one side, and swallowing and speaking clearly may be difficult. This is facial palsy, also known as Bell's palsy.
- Hydrocephalus: If a large tumor presses against the brainstem, this can affect the flow of fluid between the spinal cord and the brain. If fluid accumulates in the head, it can lead to hydrocephalus.
There is no way to prevent acoustic neuroma, but scientists are looking at ways of using gene therapy to control the overproduction of Schwann cells.
Anyone who is interested in clinical trials for acoustic neuroma can click here for more information.