Overview

A neuroma is a benign tumor that grows from nerve cells. The term acoustic neuroma is a misnomer. These tumors grow from Schwann cells that form the sheath covering a nerve  and are more accurately called schwannomas. Benign (not cancerous) tumors do not spread to other parts of the body. Neuromas generally grow slowly and most often arise from the fifth (trigeminal) and eighth (vestibulocochlear) cranial nerves, but can arise from any of the 12 cranial nerves.

What is an acoustic neuroma?

An acoustic neuroma is a tumor that grows from the sheath (covering) of the eighth cranial nerve. The eighth cranial nerve, also known as the vestibulocochlear nerve, is a bundle of nerves responsible for hearing and balance. This bundle consists of the cochlear nerve (responsible for hearing) and the superior vestibular and inferior vestibular nerves (responsible for balance). Acoustic neuromas arise from the vestibular nerves and are therefore more accurately termed vestibular schwannomas. The vestibulocochlear nerve lies next to the facial nerve within the bony internal auditory canal (Fig. 1). The facial nerve (seventh cranial nerve) controls the muscles of the face. The close relationship of the vestibulocochlear nerve to the facial nerve explains why facial weakness can occur when the tumor grows large.

Acoustic neuromas are classified according to their size as small (less than 1.5 cm), medium (1.5 to 3 cm), or large (more than 3 cm). As the tumor grows it expands from its origin within the internal auditory canal into the space known as the cerebellopontine (CP) angle. Within the CP angle the tumor can enlarge to compress the brainstem and the trigeminal nerve, which is responsible for facial sensation.

What are the symptoms?

The most common first symptom is hearing loss in the affected ear, which may often go unrecognized or mistaken as a normal change of aging. 

The symptoms associated with acoustic neuromas follow the size and growth of the tumor. Small intracanalicular tumors are typically limited to the eighth nerve causing hearing loss in one ear, tinnitus (ringing in the ears), and unsteadiness. As the tumor grows and expands into the cerebellopontine angle, hearing loss may worsen and vertigo gradually becomes replaced by dysequilibrium. Large tumors can compress the brainstem causing trigeminal symptoms of facial numbness, initially in the mid-facial region. As brainstem compression becomes severe, the fourth ventricle collapses and hydrocephalus results. Chronic hydrocephalus frequently results in persistent headache and visual loss.

What are the causes?

What causes a tumor to grow is largely unknown. Acoustic neuromas can be sporadic or caused by an inherited condition called neurofibromatosis type 2 (NF-2) (also known as van Recklinghausen's disease). Sporadic tumors occur 95% of the time while 5% of acoustic neuroma patients are discovered or known to be NF-2 patients. NF-2 is a rare disease characterized by multiple tumors in various sites, especially the skin, and can cause bilateral acoustic tumors. 

Who is affected?

Acoustic neuromas affect about 10 people in one million. More women than men are affected and are usually diagnosed between the ages of 30 and 60 years. 

How is a diagnosis made?

First, the doctor will ask about your personal and family medical history and perform a complete physical examination. In addition to checking your general health, the doctor performs a neurological exam. This includes checks for mental status and memory, cranial nerve function (sight, hearing, smell, tongue and facial movement), muscle strength, coordination, reflexes, and response to pain. The doctor may order diagnostic tests such as:

Audiogram is a test performed to effectively evaluate hearing in both ears. This test is important to begin the diagnosis of acoustic neuroma. 

Computed Tomography (CT) scan is a safe, noninvasive X-ray to review the anatomical structures within the brain.  It is especially useful for viewing changes in bony structures. The characteristic finding of an acoustic neuroma is widening of the bony internal auditory canal.

Magnetic Resonance Imaging (MRI) scan is a safe, noninvasive test that gives a more detailed view of the brain structure. A contrast agent called gadolinium is sometimes injected into the bloodstream during scanning to make tumors more visible. The scanning can be confining and noisy to some patients. Metal objects need to be removed before having the scan done because of the magnetic signals produced by the scan. An MRA (Magnetic Resonance Angiogram) is the same noninvasive study, except it is also an angiogram, which means it also examines the blood vessels, as well as the structures of the brain. 

What treatments are available?

The larger the tumor -- the more complex the treatment. Therefore, early recognition, diagnosis, and treatment are essential. Generally, the recommended treatment for an acoustic neuroma is surgical removal by a neurosurgeon and an otologist. 

Observation
Sometimes the best treatment may be no treatment. Acoustic tumors that are small and have few symptoms may be observed with routine MRI scans every year until the tumor growth or symptoms necessitate surgery. Observation may be the best option for older patients with other health conditions or patients with a tumor in their only hearing ear. 

Surgery
The priorities in surgery are first the preservation of life, second the maintenance of facial nerve function, and third the preservation of socially useful hearing in the tumor ear when possible. There are several surgical approaches to remove the tumor. The choice of a particular approach depends on several factors, including tumor size, tumor position, hearing status, and general health of the patient. 

Stereotactic Radiosurgery
Stereotactic radiosurgery uses a single highly concentrated and precisely directed beam of radiation to treat brain tumors safely, effectively, and without an incision. The procedure is performed on an outpatient basis. A metal frame is attached to the patient's head by four pins. While wearing the frame the patient is scanned in the MRI. Using the frame as reference points, the exact location of the tumor is determined three-dimensionally in a computer. Surgeons then use highly focused beams of radiation to damage the tumor and stop its growth. 

Currently there are two types of radiosurgery technologies: the LINAC and Gamma Knife. The Gamma Knife, a hemispheric device that surrounds the patient's head, targets 201 beams of cobalt-60 radiation on the tumor. Each beam travels through a different area of the brain. By itself, it is weak enough not to harm the tissue it passes through. The beams overlap in the target area, and where they intersect, they create a lesion. The other type, LINAC, is a typical linear accelerator that rotates around the patient, producing multiple beams of radiation; each arcs toward the target on the tumor through different tissue. Where the beams converge, they cause slight damage. 

The effects of radiation treatment occur over a period of time so the tumor will not show immediate results. Gradually, the lesion stops growing and in some cases may shrink in size.

What happens before surgery?

You may be scheduled for presurgical tests (e.g., blood test, electrocardiogram, chestX-ray) several days before surgery.An audiologist will perform a hearing test and a presurgical assessment of cranial nerve function. Your tumor ear may be temporarily painted with a dye to ensure that the correct ear is identified for surgery. In the doctors office you will sign consent forms and fill out paperwork so that the surgeon knows your medical history (allergies, medicines/ vitamins, bleeding history, anesthesia reactions, previous surgeries). You may wish to donate blood several weeks before surgery. You should stop taking all non-steroidal anti-inflammatory medicines (Naproxin, Advil, etc.) and blood thinners (coumadin, aspirin, etc.) one week before surgery. Additionally, stop smoking, chewing tobacco, and drinking alcohol one week before and 2 weeks after surgery as these activities can cause bleeding problems.

• Middle fossa approach is generally used for small intracanalicular tumors where preservation of facial nerve function and hearing is optimal.
• Suboccipital approach (also called the retrosigmoid) allows the surgeon to remove small and large tumors while preserving facial nerve function and a degree of functional hearing if possible.
• Translabyrinthine approach is usually used if patients already have hearing loss or the tumor size and position indictate removing the labyrinth.

What happens during surgery?

Step 1: Preparing the patient
You will be taken to the operating room and transferred to an operating table. The anesthesiologist will begin an intravenous line in your arm, insert a urinary catheter, and have you breathe gas to put you to sleep. Once asleep, your body will be positioned for the surgery and your head secured in a head fixation device attached to the operating table. The audiologist will attach electrodes to your face and ear to monitor the facial nerve, hearing, and brainstem functions (hearing is not monitored during the translabyrinthine approach).

Step 2: Opening the skull  (Fig. 3)

Suboccipital approach (retrosigmoid)
A skin incision is made at the back of the head behind the ear to expose the skull. Next, a high-speed drill is used to cut a bone flap, or craniotomy, in the skull. The tough outer covering of the brain, called the dura mater, is opened with scissors to expose the cerebellum. Retractors are used to hold back the cerebellum, allowing the surgeon to see the acoustic neuroma and the seventh-eighth cranial nerves. Facial nerve function and hearing are monitored during surgery.

Translabyrinthine approach
A curved skin incision is made behind the ear to expose the skull. Next, a drill is used to remove the bone of the mastoid region, exposing the semicircular canals of the labyrinth. The labyrinth is removed with a drill and the dura of the auditory canal is identified. The dura is opened exposing the eighth nerve and tumor. Facial nerve function is monitored during surgery. This approach destroys the hearing and balance organs of the affected ear. However, balance control in the opposite ear usually provides stabilization for the patient within 1 to 4 months.

Middle fossa approach
A horseshoe-shaped skin incision is made starting in front of the ear and then arching behind it. A drill is used to remove the bone above the ear in the temporal area. The dura covering the temporal lobe of the brain is retracted. Bone overlying the auditory canal is removed to expose the tumor and seventh-eighth cranial nerves. Facial nerve function and hearing are monitored during surgery.

Step 3: Removing the tumor
Once the tumor is exposed, the surgeon assesses the tumor's origin and its attachment or involvement of other brain structures (Fig. 4). Acoustic tumors, depending on their size, can be attached to the seventh nerve, fifth nerve, ninth nerve, brainstem, or the anterior inferior cerebellar artery. The surgeon uses a variety of tools such as scissors, knife, cautery, ultrasonic aspirator, and laser to dissect and remove the tumor. If the tumor is large or is wrapped around the eighth nerve, the nerve may be cut to remove the tumor. Tumor attachment to the seventh nerve is carefully dissected to preserve the nerve because the seventh nerve is responsible for facial movement. Damage to the seventh nerve may result in facial palsy. Throughout the tumor removal, the audiologist monitors the function of the cranial nerves and the brainstem. Every effort is made to totally remove the tumor without damaging hearing, facial nerve function, and vital brainstem functions. In some cases it may be necessary to remove only part of the tumor, leaving small remnants of tumor attached to critical structures. Because these tumors grow slowly, yearly follow-up examinations will watch for regrowth and accordingly a decision made regarding another surgical removal.

Step 4: Repair of the facial nerve (if necessary)
In some cases it may be necessary to cut the facial nerve to remove the tumor. When this happens it is possible to repair the cut nerve with several techniques. If the two cut ends of the nerve are long enough, they may be reattached to each other - this is a direct nerve repair. If the two cut ends are not long enough, a section of another nerve may be grafted between them - this is an interposition nerve graft. The graft usually comes from a nerve in the neck that innervates the earlobe. Sometimes it is not possible to repair the facial nerve at the time of surgery, in these cases other surgical options are available as a second procedure after recovery from tumor removal.

Step 5: Closing the craniotomy
After the tumor has been removed, the dura is closed and biologic glue is applied to reduce cerebrospinal fluid (CSF) leakage. The bone flap is put back in place and secured with plates. The muscles and skin incisions are then rejoined and sutured together. 

What happens after surgery?

You will be taken to the neurointensive care unit for 24 hours and remain in the hospital for 5 days. Following surgery, you may experience headache, nausea, unsteadiness, or lack of coordination. These symptoms usually reside over a period of weeks. Your physician will discuss whether physical or occupational therapy is indicated. 

What are the results of treatment?

Removing the tumor will hopefully restore your balance, facial function and sensation, eyelid function, and tear production. Hearing loss is usually permanent because the tumor is wrapped around the eighth cranial nerve (the nerve responsible for hearing). The results of your surgery are directly related to the size of the tumor and the surgical approach used to remove the tumor. The Acoustic Neuroma Association collects and publishes outcome data from member surveys and can be obtained from them.

What are the side effects of treatment?

• Hearing loss is the most common complication and is usually permanent in the affected ear because the tumor is wrapped around the eighth cranial nerve (the nerve responsible for hearing). In small tumors it is possible to save hearing by removing the tumor. Larger tumors usually have already caused a variety of hearing problems prior to surgery. Understanding speech in difficult listening situations may be helped with a CROS (contralateral routing of sound) aid. The CROS aid is an instrument that receives sound on the deaf side, amplifies it, and then routes it to the good hearing ear. A small aid is worn on each ear.

• Facial paralysis is the loss of muscle control on one side of the face caused by nerve swelling or damage; it may be temporary or permanent. Postoperative facial nerve paralysis is usually directly related to the size of the tumor. Temporary facial paralysis is common after surgical tumor removal and weakness may persist for 6 to 12 months. Permanent facial paralysis is less common (usually in large tumors) and results in an inability to close the eye, loss of facial expression, and facial droop. Facial reanimation procedures attempt to restore facial tone. One option is a facial-hypoglossal nerve anastomosis, which the facial nerve in the neck is connected to the hypoglossal nerve (controls the tongue and swallowing) (Fig. 5). Another option involves repositioning a portion of the temporalis muscle (responsible for chewing) and attaching it to the sagging facial muscles. Other strategies include plastic surgery to suspend the face, and placement of a gold weight in the eyelid to facilitate eye closure.
  
  A facial-hypoglossal nerve anastomosis can be performed in the neck to achieve facial re-animation. After the procedure partial voluntary movement can return and is initiated by tongue movement. This technique is recommended as soon as there is no possibility of facial nerve function. After several years of facial paralysis the facial nerve may become filled with scar tissue and unresponsive. A side effect of this procedure is the possibility of tongue paralysis or atrophy on the affected side.

• Eye problems are usually the result of facial paralysis allowing the eye to become dry and unprotected. Care by an eye specialist may be indicated. Artificial tears, eye lubricants, protective glasses, bandage contact lenses, and taping the eye shut are all options to protect the cornea. When prolonged facial nerve paralysis is expected, various surgical procedures may be performed to protect the cornea and improve one's appearance. For example to improve eyelid position and closure, a canthoplasty which is the bringing together of the tendon arms in the corners of the eye may be performed. To simulate blinking, a palpebral spring device may be inserted in the upper eyelid to provide a blink reflex synchronous with the other eye or a silastic elastic prosthesis may be secured through and around the upper and lower eyelids. Alternatively, a gold weight may be implanted in the upper eyelid to enhance lid closure or the upper and lower eyelids may be sewn shut (tarsorrhaphy).

• Dizziness and balance disturbances are usually cured by tumor removal. However, if the labyrinth was removed during surgery (translabyrinthine approach), dizziness is common until the opposite ear can compensate and usually provides stabilization for the patient within 1 to 4 months. Compensation may never be perfect particularly in darkness, when a person is fatigued, or during a sudden change in body position.

• Cerebrospinal fluid (CSF) leakage is the escape of cerebrospinal fluid from around the brain through small holes in the dura and may occur in some cases. This usually occurs as a constant nasal drip of clear fluid that is particularly noticeable when bending over. Often leakage is temporary and will close off on its own. If not, a second operation may be necessary. New closure techniques and use of biologic glue greatly reduces CSF leakage.

• Headache is common immediately after acoustic neuroma surgery and usually subsides within several weeks. Persistent headache more often occurs because of two factors: the surgical approach (suboccipital) used and the tumor size.

If you have more questions, please contact the Mayfield Clinic at 800-325-7787 or 513-221-1100. Additional information is available on the web.

Support groups are available through the Acoustic Neuroma Association, 600 Peachtree Pkwy, Suite 108, Cumming, GA 30041, Phone: (770) 205-8211 or on the web at www.anausa.org and www.ANarchive.org.

American Brain Tumor Association www.abta.org or 1.800.886.2282

National Brain Tumor Foundation www.braintumor.org or 1-800-934-CURE

Glossary

acoustic nerve: the eighth cranial nerve, also known as the vestibulocochlear nerve, is responsible for hearing and balance.
 
audiogram: a test of hearing acuity.

brainstem: connects the upper brain to the spinal cord; responsible for autonomic functions such as breathing and heart rate.

cerebrospinal fluid: a watery fluid which flows within the ventricles and around the surface of the brain and spinal cord.

craniotomy: a surgical opening in the skull.

facial nerve: the seventh cranial nerve, responsible for movement of the face. 

facial palsy: paralysis of the facial muscles on one side.
 
labyrinth: part of the internal ear responsible for balance.
 
neuroma: tumor originating from nerve cells; also called neurinoma, schwannoma.
 
neurofibromatosis: an inherited condition characterized by multiple tumors in various sites, especially the skin; can cause bilateral acoustic tumors. 

tinnitus: ringing in the ears. 

vertigo: dizziness. 

updated: 6.2004
reviewed by > John Tew, MD and Nancy McMahon, RN