In the later stages, acoustic neuroma may affect the nerves of the cerebellum and brainstem, and it can increase pressure in the brain, which can be life-threatening.
Acoustic neuroma is also known as acoustic neurinoma, vestibular schwannoma, and auditory tumor.
A layer of cells, called Schwann cells, covers nearly all healthy nerves. Schwann cells provide insulation and support for nerve impulses; if they begin to multiply too quickly, acoustic neuroma occurs. Between 2,000 and 3,000 new cases are diagnosed each year in the United States, or around 10 per million people.
Treatment for acoustic neuroma depends on several factors, including the patient's age and general health, and the location and size of the tumor. In some cases, watchful waiting is recommended, and if the tumor is small or slow-growing, no further action may be taken.
Treatment options include:
Stereotactic radiosurgery - the doctor can deliver radiation precisely to the tumor without having to cut into the patient. A lightweight head frame is attached to the patient's scalp, which has been numbed. The tumor is precisely located with the help of imaging scans - the scans help determine where exactly to apply the radiation beams. The patient may experience neck stiffness and nausea.
Microsurgical removal - this involves removing a tumor through an incision in the skull. It is carried out under general anesthesia. In about 95 percent of cases, surgery controls the tumor. If the tumor is very small and nerve damage is minimal, hearing may be saved and symptoms improve.
Rarely bits of the tumor may be left behind if the surgeon believes there may be a risk of nerve damage. If this is the case, radiotherapy may be used to finish them off.Radiation therapy - radiotherapy may be used instead of conventional surgery, to reduce the size or limit the growth of the tumor. It is sometimes used after surgery, to remove any remaining traces of the tumor. The radiation is carefully targeted to minimize damage to healthy tissue surrounding the tumor.
Radiosurgery - this type of treatment delivers radiation directly to the tumor. Imaging scans are used to locate the tumor. A frame is attached to the patient's scalp to achieve this treatment, which can cause stiffness or nausea.
Monitoring and MRI - as many acoustic neuromas do not grow, continuous monitoring may mean treatment is not required. In this case, MRI (magnetic resonance imaging) scans can determine the growth of the tumor.After surgery, a doctor will monitor the patient's recovery and check for recurrence of symptoms.
Potential for hearing loss
Some patients have a degree of permanent hearing loss after surgery. This usually depends on the size of the tumor. The risk is higher if a tumor is over 1.5 centimeters across.
If a patient has neurofibromatosis type 2, and if tumors have developed on both acoustic nerves, the patient may be unable to hear with either ear after surgery.
In this case, doctors prefer to delay surgery for as long as possible.
Acoustic neuroma symptoms commonly include hearing loss.
The location of the tumor in the inner ear means there are a range of potential symptoms. These include:
- Hearing loss - one of the first symptoms of an acoustic neuroma is gradual hearing loss in one ear, while hearing in the other ear remains normal. Unilateral hearing loss occurs in 90 percent of patients with the condition.
- Tinnitus - over 80 percent of patients will also have tinnitus, or ringing in the affected ear.
- Earache - there may be an earache in some cases.
- Dizziness, loss of balance and vertigo - the person may experience these symptoms is the tumor is affected the inner ear.
- Loss of sensation - if a large tumor develops and compresses a part of the brainstem, local cranial nerves may be impacted. The trigeminal nerve may be affected, leading to loss of sensation on one side of the face and mouth. The back half of the tongue may lose its sense of taste.
- Headaches - larger tumors can increase the pressure in the brain, leading to headaches, vomiting, and altered consciousness.
- Vision issues - in rare cases vision problems occasionally occur.
Acoustic neuroma is a slow-growing tumor, but without treatment, it can push against vital brain structures and become life threatening.
Acoustic neuroma size grading
Tumors are classified as small when they are under 1.5 centimeters in size, medium when they are 1.5 to 2.5 centimeters, and large if they measure 2.5 centimeters or more. A person with a small tumor may not experience symptoms, but this is not always the case. It depends on where the tumor is located.
Family history and genealogy is a significant risk factor for acoustic neuroma.
The exact cause of acoustic neuroma is unclear. According to the American Hearing Research Foundation, around 95 percent of cases are sporadic, with no known cause.
Risk factors appear to include:
- Age - most people develop acoustic neuroma between the ages of 30 and 60 years.
- Family history of neurofibromatosis type 2 - around 5 percent of people with acoustic neuroma have neurofibromatosis type 2 (NF-2), in which a person develops acoustic neuromas on both auditory nerves.
- Radiation exposure - there is a small chance that low-dose exposure to radiation to the head and neck during childhood may increase the risk.
Some studies have suggested that it may be related to cell phone use or long-term exposure to loud noise, but other research has not confirmed this.
If a physician suspects an acoustic neuroma, they may request an MRI or CT scan of the head.
To rule out other causes of dizziness, hearing loss, or vertigo, the patient may undergo a hearing test, a balance test, and a test for brainstem function.
There are several complications of acoustic neuroma including:
- Hearing loss - this can undermine the individual's quality of life, leading to work and social problems. Sometimes, hearing loss persists after treatment.
- Lifestyle impact - dizziness and loss of balance can make daily activities difficult to do.
- Facial palsy - If the patient's facial nerve, which is very close to the acoustic nerve, is damaged during surgery, they may experience facial palsy, where the face droops on one side. Swallowing and speaking clearly may be difficult.
- Hydrocephalus - a large tumor may press against the brainstem. This can interfere with the flow of fluid between the spinal cord and the brain. As the 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.