Acoustic Neuroma
Jack M Kartush, MD

Hearing loss, ringing of the ears and dizziness are common complaints that are usually due to common causes. Occasionally, however, these symptoms may be due to a benign tumor that grows between the inner ear and the brain.

The most common inner ear tumor is an acoustic neuroma which originates on the hearing and balance nerves. It begins its growth within the inner ear but eventually grows in towards the brain. Although it is benign, it can cause serious problems for nerves, brain and life due to its size and location among vital structures.

Until recent years, it was very hard to diagnose these tumors until they became quite large. At that point removing the tumor had great risks. Today, sophisticated scans and computerized tests help find many tumors when they are small and much easier to remove. In addition, many technical breakthroughs have made surgery of even the largest tumors much safer.

There is no known cause for these tumors and they are not known to run in families. They tend to grow very slowly and are only rarely seen in children.

There is, however, an unusual variety that can run in families. This is called neurofibromatosis . Unfortunately, these people may have many tumors throughout their body and will often have two inner ear tumors. This can be readily diagnosed with scans.

I'd like to review some of the anatomy of the inner ear to give a better understanding of these tumors and how they are treated.

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Anatomy and Physiology

There are two parts of hearing: mechanical and electrical. The mechanical part picks up sound from the outer ear canal and then vibrates the ear drum and three tiny hearing bones in the middle ear.

The Eustachian tube is the natural connection between the ear and the nose and throat.

The inner ear looks a bit like a snail or a maze. Doctors refer to it as the labyrinth. It has two halves which are connected and are filled with fluid.

The coil or cochlea takes care of the nerve-part of hearing. Like a telephone, it takes the vibration and turns it into an electric signal that is relayed to the brain.

The other half of the inner ear is the balance or vestibular system. There are three fluid-filled balance canals.

In close association to the ear is the facial nerve. It helps move the face and also provides for some of the taste fibers to the tip of the tongue.

At the deepest level is the brain from where the hearing, balance and facial nerves originate.

Acoustic Neuroma

Acoustic neuromas begin within the internal auditory canal. This is a small opening which carries the hearing, balance and facial nerves. The tumor most commonly starts on the balance nerve but all of the nerves become involved as the tumor enlarges. There are three surgical approaches that can be used to remove these tumors. Each has its own pro's and con's that have to be weighed depending on tumor size, tumor location and whether or not there remains any usable hearing in the ear. Other important factors include the patient's age, health and occupation.

For many years, acoustic neuromas were removed exclusively by neurosurgeons through a standard approach called a suboccipital craniotomy. This entailed opening the back of the skull and moving the brain over until the tumor could be seen growing out of the inner ear. Because tumors were often not diagnosed until they were very large and because the suboccipital approach required a considerable amount of brain retraction before the tumor could even be seen, the risk of death , stroke and a paralyzed face was extremely high.

Acoustic neuromas have often been diagnosed by ear specialists (otologists) because the first signs of tumor growth are hearing loss, tinnitus and dizziness. Not until late does the tumor begin pressing on the brain to cause headaches, facial paralysis and loss of vision. Therefore, many otologists became frustrated that the patients whom they referred often developed serious complications following suboccipital removal of their neuroma.

In the late 1950's, otologists began working with neurosurgeons to develop safer ways of removing the neuromas. One of the greatest innovations was to use a microscope to do the delicate work adjacent to the brain and nerves. Like any new idea, this initially caused great controversy and emotion. Today, however, there is virtually no surgeon in the world who removes neuromas without a microscope.

Another innovation was to remove the tumor through a more direct approach. Because these tumors always originate adjacent to the inner ear, a surgical approach through the inner ear meant that much less brain manipulation would be required compared to suboccipital surgery.

Therefore, the safest treatment is to remove these tumors by a directly exposing the them by going directly through the inner ear . This approach is called translabyrinthine surgery. Its advantage is that it is the most direct exposure of the tumor with the least pressure on the brain. Its disadvantage is that, by going directly through the inner ear, any residual hearing is completely lost. Because most patients with acoustic neuromas have little or no usable hearing, this disadvantage is of little concern.

By the time the tumor is diagnosed most patients have little usable hearing.

If the tumor is found to be very small and lying within the internal auditory canal, a middle cranial fossa surgery can be used in an attempt to preserve the hearing nerve if useful hearing is present preoperatively. In order to spare the inner ear, this approach requires that the temporal lobe of the brain be lifted. Because acoustic neuromas always adhere to the hearing nerve, the success rate for preserving hearing with small tumors is about 50 to 60%. Once a tumor starts has grown to about one inch in size, the chance of being able to spare the hearing nerve is very poor even if hearing is good before surgery.

Today, the suboccipital approach has been refined to make it safer as well. It is now performed using the microscope and the skull opening is made much closer to the ear in order to minimize brain retraction. We refer to this refined approach as retrosigmoid surgery. It can be particularly helpful for very large tumors or for small tumors that originate close to the brain rather than the inner ear. Like the middle cranial fossa approach, this technique allows the possibility for hearing preservation in some patients.

Acoustic Neuroma Surgical Photos - SENSITIVE

Facial Nerve

Many factors must be considered in deciding which approach is most suitable for a given tumor. Although there is often much discussion regarding whether or not any hearing can be saved, of greater importance is minimizing risk to life, brain and the facial nerve. In early years using the suboccipital approach, virtually every patient awoke from surgery with a paralyzed face. It was just too difficult to peal the sticky tumor without tearing or stretching the facial nerve. Many neurosurgeons concluded that a paralyzed face was a reasonable price to pay for removing an acoustic neuroma.

Fortunately, microsurgery and improved approaches have dramatically improved our ability to save the facial nerve in the majority of patients. A major innovation has been the use of facial nerve monitoring. Pioneered here at the Michigan Ear Institute, monitoring the facial nerve with a special computer during surgery has allowed a dramatic improvement in preserving facial nerve function. The monitoring computer acts like an early warning system to alert the surgeon to pressure or stretching of the nerve. A videotape is available which describes this technique in detail.

SURGICAL APPROACH

  Translabyrinthine Middle Fossa Retrosigmoid
Brain retraction Least Moderate Most
Facial nerve safety Best Moderate Moderate
Hearing preservation None Moderate Moderate
Persistent headaches Occasional Rare Moderate
Recovery time Moderate Shortest Moderate

Emphasis on safety and function

Centers around the world that have the highest success rate and the lowest complication usually see a high volume of patients and establish a team ot otologists and neurosurgeons as has been done at the Michigan Ear Institute. The operation often takes the better part of a day to complete in order to do so safely underneath the operating microscope.

In some patients, the tumor may burrow into the facial nerve or brainstem. This may require that a small amount of residual be left behind in order to reduce the risk of facial palsy or stroke. Under these circumstances, there are two possibilities. If there is only a tiny fleck of tumor that remains, it may wither away from lack of a blood supply. A laser can sometimes be used to further shrivel up or char this last bit of tumor. In other patients, the remaining amount needs to be removed during a second operation which may not be needed for up to a year following the initial surgery. Either way, repeat scans are used to check the status of the residual tumor.

Although patients greatest concerns naturally focus on the risks to life, brain and the nerves, modern techniques have made tremendous gains in reducing these complications. Therefore, it�s important to know some of the other less concerning but more common side effects.

Two of the most common complications of acoustic tumor surgery are leakage of spinal fluid and postoperative infections. Spinal fluid coats the nerves and tumor. After surgery, the opening must be repaired with nearby muscle or a graft of the patient's own belly fat in order to reduce the chance of spinal fluid leak through the inscision, the ear or the nose because all these areas are inter-connected. Should a leakage occur despite this, additional packing or a spinal fluid drain may be required.

Infections are minimized by using powerful antibiotics the day of surgery as a preventative measure. Should infection occur despite this, additional time for IV antibiotics would be required.

Dizziness is expected after acoustic tumor surgery. In some cases, unsteadiness can be prolonged although spinning vertigo tends to subside after the first day or two. The best treatments are head exercises and walking.

Because the tumor always adheres to the facial nerve, facial weakness is a possibility despite all the best attempts particularly with large tumors which squeeze the facial nerve so thin that it may barely be recognizable.

Even some small tumors, however, may be difficult to separate from the facial nerve if, like a weed, they burrow into the nerve rather than just stick to the side of if.

Facial weakness may be temporary or permanent. Time is required to see how well the nerve may recover. During this time, the eye may become dry and have trouble closing. This is treated using eye drops and a tiny gold bar implanted just beneath the eyelid skin. It can be easily removed if facial function recovers.

Many patients with acoustic tumors have tinnitus or ringing of the ears. Typically this improves a bit after surgery but most patients are advised to expect it to be about the same. Rarely, it may disappear after surgery or get worse.

Postop Expectations

The incision behind the ear is closed with nonabsorbable stitches which are removed in about three weeks. For the first week, keep the incision dry by covering it with a washcloth during showers. Pat it dry or use a hair dryer if it gets wet. After the first week, you may wash your incision but be gentle, don�t soak in a tub and avoid picking at crusts.

Avoid hard nose blowing or heavy lifting which could bring about a leakage of spinal fluid.

Stuffiness and hearing loss can be expected even in cases where the hearing may have been saved. This often improve slowly as your body absorbs the healing fluids. In the meantime you can expect to hear inner ear noises and your own heartbeat.

Dizziness is common after this type of surgery. Be sure to ask your doctor how soon you may return to work or driving.

Other Tumors

Although acoustic neuroma is the most common tumor of the inner ear, other similar tumors can be found in this area. Tumor type often cannot be determined until they are seen at the time of surgery. Menigiomas are benign brain tumors that may grow into the ear. Facial nerve neuromas are similar to acoustic neuromas but because they grow from the facial nerve itself, a facial palsy is almost always expected although repairing the nerve with a graft typically allows a moderate degree of function as the nerve slowly regenerates over about a year.

Observation & Radiation

The safest time to remove the tumor is when it is smallest. Because these tumors grow slowly, surgery is rarely needed urgently but it should be done in a timely fashion because the complications of surgical removal increase as the tumor grows in size.

On rare occasions, however, a doctor might recommend observing the tumor rather than removing it if a tiny neuroma is found in an elderly, ill patient. Scans usually need to be repeated every six months. The idea is to see if the tumor might grow slowly enough that by the time the patient has died from other causes, surgery will have been avoided. Such a plan, of course, is not sensible for most patients.

Some doctors are currently experimenting to see if different types of radiation therapy such as the so-called gamma knife may be useful for some acoustic tumor patients particularly for the elderly. Much research, however, is still required to see how effective it may be and what the short and long term side effects are if high dose radiation is used near the brain for benign rather than malignant tumors.

Conclusion

Microsurgical technique, lasers and the use of facial nerve monitoring have dramatically improved the safety of removing acoustic tumors.

There is no one best approach. Each case needs to be looked at individually.

Hopefully, this presentation has made the topic a bit more understandable.

Be sure to discuss any details in greater length with your own doctor.



 
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