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An acoustic neuroma is a benign (non-cancerous), slow-growing tumor. The tumor tends to grow at a rate of only 1-10mm each year. As it is benign, it will not spread to other tissue. Acoustic neuromas arise from the major nerve that is associated with balance and hearing. The nerve is located in the brain, and is known as the vestibulocochlear nerve, which is the eighth (out of twelve) cranial nerve.
Usually the tumor originates from the cells that wrap around the the nerve; the specific cell of origin is called a Schwann cell. Therefore, the tumor is more accurately referred to as a "vestibular schwannoma".
Typically, the tumor is located in an area of the brain called the cerebellopontine angle (CPA). This area is extremely close to the brainstem, a vital section of the brain The brainstem functions to regulate many important systems, such as breathing.
These tumors account for 6-8% of all intracranial tumors. One out of every one-hundred thousand persons is affected. Females are twice as likely to be affected than males. 95% of the time only one side is involved (right or left). The tumor is sometimes associated with a genetic disorder called Neurofibromatosis Type 2. In this case, there are usually tumors on both sides (right and left}.
The three most common symptoms are hearing loss, ringing in the ears, and disequilibrium (loss of balance and dizziness). Hearing loss is usually slow and gradual. High frequency sounds are difficult to hear and people usually complain of difficulty with telephone conversations. About ten percent of patients have sudden hearing loss. Researchers believe this is due to an infarction of the nerve or occlusion (obstruction) of an artery supplying the inner ear (cochlear artery). The ringing is usually high-pitched.
Some patients experience facial numbness, facial weakness, ear pain, and taste changes. These symptoms are due to the tumor pushing on nearby nerves. When discovered, the tumor is usually greater than 2 centimeters in diameter. With larger tumors there can be pressure on the brainstem. If this happens the patient may experience headache, nausea, vomiting, double vision, and, in rare cases, even coma or death.
A magnetic resonance image (MRI) is the best imaging study for this condition. The MRI will reveal the size and exact location of the tumor. These details are extremely important for the neurosurgeon.
In addition, all patients should have a formal hearing test. Other useful tests that might be used to differentiate the condition form other causes of dizziness and vertigo include:
The surgeon takes into account the size and location of the tumor, the patient’s hearing quality, the patient’s age and medical condition, and of course the patient’s wishes. The three treatment options are observation, surgery, and radiation.
Your neurosurgeon may choose to watch the tumor with serial MRI scans and periodic exams if he feels your symptoms and other medical issues do not warrant surgery. Some authorities say that if the tumor grows greater than 2 millimeters per year, then more aggressive treatment is indicated.
Another treatment option is stereotactic radiosurgery, often called Gamma Knife radiosurgery. This is a form of focused radiation to the tumor. This form of therapy can be considered in small to medium sized tumors that are not causing any brainstem compression. The goal of radiosurgery is tumor control and not tumor removal. The attraction of this option is that it avoids some of the potential complications associated with a surgical approach, while effectively reducing the size of the tumor or at least slowing its growth.
The most common treatment for patients with symptoms is surgical resection (removal) of the tumor. The approach to the tumor depends on its size and the patient’s quality of hearing (as surgery can risk further hearing loss).
Most experts agree that young patients should have early intervention. The goal of surgery is long-term tumor control. Complete removal of the tumor results in a less than 1% recurrence rate. Partial resection (removal) usually does not require another future operation.
The most common complication of surgery is a leak of cerebrospinal fluid, the liquid that nourishes the brain. If there is a leak after surgery, the neurosurgeon will treat the problem accordingly. Other risks of surgery include injury to other nerves. One of the most common nerves that suffers injury is the facial nerve. The facial nerve controls the muscles in the face. Many surgical outcomes are based on the facial nerve’s function after surgery (House-Brackman Scale). Typically, 1 out of 5 patients will have noticeable facial weakness.
Recovery and Prognosis
Brain surgery results in complete removal of the tumor in more than 95% of cases. Of those patients with relatively small tumors, about 95% will have no permanent facial paralysis following surgery. However, roughly two-thirds of patients with large tumors will have some permanent facial weakness following surgery.
Preservation of a patient’s hearing will depend in part on the size of the tumor when it was discovered and treated. If a tumor is removed when it is very small, approximately 50% of patients will retain useful hearing in the affected ear. Any hearing that is lost prior to surgery will not be regained. Large tumors usually result in total loss of hearing on the affected side.
Reference: Long-Term Outcomes after Radiosurgery for Acoustic Neuromas
Douglas Kondziolka, M.D., L. Dade Lunsford, M.D., Mark R. McLaughlin, M.D., and John C. Flickinger, M.D. | N Engl J Med 1998; 339:1426-1433 | November 12, 1998 DOI: 10.1056/NEJM199811123392003
LastUpdate: 2017-07-21 09:16:29