Treatment Options for Acoustic Neuromas

Loss of hearing is common in older people, but when a younger person experiences a hearing loss, especially on just one side, it could indicate a relatively rare tumor called an acoustic neuroma. Acoustic neuromas usually begin in a tiny, bony tube called the internal auditory canal - the passage carrying nerves and blood vessels between the inner ear, where the hearing and balance mechanisms are located - and the brain. As the tumor grows inside this bony tube and then out against the brain, it distorts adjacent nerves and can affect balance as well as hearing. About 2,000 acoustic neuromas are diagnosed in the United States annually.

The good news is that acoustic neuromas are benign (non-cancerous) and usually slow-growing. And in just the past few years, technological advances have significantly improved early diagnosis and expanded treatment options for acoustic neuroma, says P. Ashley Wackym, MD, John C. Koss Professor and Chairman of the Department of Otolaryngology and Communication Sciences at the Medical College of Wisconsin. He is one of the few board-certified Neurotologists practicing in Wisconsin and in addition to his training in otolaryngology-head and neck surgery, he has completed fellowship training in adult and pediatric otology, neuro-otology and cranial base surgery.

The Acoustic Neuroma Association recommends patients seek treatment from a medical team with substantial acoustic neuroma experience. Dr. Wackym and his neurosurgical partner Dr. Glenn Meyer have had more experience diagnosing and treating acoustic neuromas and other skull-base tumors than physicians in any similar program in Wisconsin, Illinois, or Iowa.

"Although unilateral (one-sided) hearing loss is a common symptom in patients with acoustic neuroma," says Dr. Wackym, "we also see patients who have symptoms of tinnitus (buzzing or ringing in the ear), vertigo (lightheadedness, dizziness, loss of balance and difficulty walking), facial numbness or pain, and in later stages, difficulty swallowing or hydrocephalus (an accumulation of spinal fluid pressing on the brain)."

Hearing Loss and Other Symptoms
In most cases, acoustic neuromas occur spontaneously, due to a mutation of a gene located on chromosome 22, Dr. Wackym says. Most spontaneous acoustic neuromas occur in patients between the ages of 30 and 60; women are affected more often than men. Estimates of the incidence vary widely - from one in every 100,000 people to one in every 3,500 people. Other studies indicate a more frequent incidence, perhaps as high as 1.5% of the population.

Occasionally, neuromas can arise from an inherited condition called neurofibromatosis type 2 (NF2), Dr. Wackym notes. These can occur in patients as young as 9 or 10, but the average age is around 20. These patients typically develop tumors on both sides and ultimately become deaf in both ears. "We are fortunate to be able to offer a prosthetic hearing device called an Auditory Brainstem Implant to help restore hearing for these patients," says Dr. Wackym. He added, "We are the only program in Wisconsin that offers this and we have been designated the Regional Center of Excellence by the manufacturer."

Unlike many brain tumors, acoustic neuromas do not invade the brain itself; nevertheless, they can have serious effects. As the neuroma grows, it can interfere with facial nerves, causing taste dysfunction and rarely, facial weakness or paralysis. If the tumor continues growing, it can press on the trigeminal nerve, causing facial numbness or pain, or press on lower cranial nerves, causing swallowing and speech problems. With extremely large tumors, pressure on the brainstem can cause life-threatening hydrocephalus.

Diagnosis Depends on Symptoms
Is diagnosis difficult? "It depends on the symptoms," Dr. Wackym says. Early detection of the acoustic neuroma - so critical in preventing serious consequences - is sometimes difficult because the symptoms can be subtle and patients may not seek treatment.

If the symptoms include hearing loss, he says, patients first undergo a thorough ear examination and hearing test (audiogram). At the Medical College of Wisconsin Acoustic Neuroma and Skull Base Surgery Program at Froedtert Hospital and the Children's Hospital of Wisconsin, diagnosis and treatment of acoustic neuromas and other skull base tumors is provided by a multidisciplinary team of specialists, including neuro-otologists like Dr. Wackym, as well as neurosurgeons, audiologists, speech pathologists, neurologists, radiation oncologists, neuro-ophthalmologists, facial plastic and reconstructive surgeons, medical geneticists and vestibular rehabilitation specialists. Audiologists use specialized hearing tests to determine whether the cochlea (part of the inner ear) and acoustic (hearing) nerves are functioning properly, as well as perform intraoperative testing when surgeons are attempting to preserve hearing during tumor removal.

In some cases, an auditory brainstem response test is performed to measure the passage of sound information from the ear through various locations in the brain. This test provides information on the passage of an electric impulse along the circuit from the inner ear to the brainstem pathways. An acoustic neuroma can interfere with the passage of this electrical impulse through the hearing nerve at the site of tumor growth in the internal auditory canal.

If abnormalities are identified with audiologic testing, the patient undergoes a Magnetic Resonance Imaging (MRI) test to confirm whether an acoustic neuroma is present, and to help doctors determine the location and size of the tumor and plan, together with the patient, which one of the three available treatment options will be used to care for the patient.

"An MRI is essentially 100% accurate in identifying acoustic neuromas," Dr. Wackym says. In addition to these tests, a facial nerve test, called facial nerve electromyography (EMG), might be done to measure the tumor's impact on the facial nerve.

Three options are available for managing an acoustic neuroma - microsurgical removal, radiation, and observation.

Microsurgical Removal
Unlike some brain tumors, acoustic neuromas can usually be surgically removed. However, because the tumor lies near vital brain centers, removing an acoustic neuroma requires the utmost precision, in both locating and excising the tumor. The exact type of operation depends on the size of the tumor and the level of hearing in the affected ear. If the tumor is small, hearing may be saved and accompanying symptoms may improve.

Larger neuromas can press on the trigeminal nerve, which controls facial sensation. Often this numbness improves after surgery; however, it may be permanent. With very large tumors, the facial nerve is stretched out over the surface of the tumor and may be temporarily or permanently weakened. If this occurs, it can result in sagging of the cheek and inability to close the eye on the affected side. There are a number of rehabilitative options ranging from facial plastic and reconstructive surgery to reanimate the face to neuromuscular facial retraining - a technique designed to facilitate recovery of function.

"The most common option selected by our patients involves microsurgery," says Dr. Wackym, in which an experienced neuro-otologist and neurosurgeon team remove the tumor using high-powered microscopes and delicate surgical instruments. Combined with advances in diagnostic imaging, these tools allow them to identify smaller tumors sooner, and achieve better results in surgery. The surgery usually lasts between 4 to 12 hours. Hospital stays range from four to seven days, with an average recovery period at home being four to six weeks.

Dr. Wackym has helped pioneer the use of surgical endoscopes in acoustic neuroma surgery to decrease complications and focus efforts on hearing and facial nerve conservation during surgery. He and his Medical College colleagues are widely recognized for their expertise in microsurgical techniques.

The Medical College group has dramatically reduced the incidence of cerebrospinal fluid leakage, a serious surgical complication that typically occurs between 5% and 20% of the time in acoustic neuroma surgery, Dr. Wackym notes. Leaking spinal fluid can lead to meningitis and other brain infections. "Our rate is just under 1%," he says. "We use surgical endoscopes to view open air cells that could fill with fluid, and seal them off so that a leak does not occur."

Radiation
The second management option is Gamma Knife radiosurgery. This is a form of stereotactic radiation therapy, a non-invasive procedure that uses high-dose rate radiation to shrink the tumor and prevent it from growing. Unlike conventional radiation therapy, in which multiple doses of radiation are delivered over several weeks of treatment, Gamma Knife radiosurgery involves only a single series of radiation doses, delivered to the precise location of the tumor over part of one day. Despite its name, Gamma Knife is not a surgical procedure. It uses advanced imaging technology to identify the exact size, shape and location of the tumor, then directs 201 converging beams of radiation on the site, sparing nearby tissue from clinically significant radiation.

"It's a great option for patients with tumors under 3 centimeters," Dr. Wackym says. "The patient can go home the same day." Unlike surgery, however, Gamma Knife does not remove the tumor, so patients need to undergo periodic MRIs to monitor whether the remaining tumor has continued to shrink, and their hearing and balance function are checked twice a year, he says. The Medical College of Wisconsin Acoustic Neuroma and Skull Base Surgery Program is one of few centers in Wisconsin to offer this technology for treatment of acoustic neuromas and is the only program that has published detailed outcomes of treatment of these tumors.

For patients who wish to divide their stereotactic radiation treatments over weeks, the surgical team has access to a LINAC-based radiosurgery system as well as the new Tomotherapy system. It uses similar localizing and treatment planning techniques used for Gamma Knife radiosurgery.

Radiation therapy is sometimes the preferred option for elderly patients, patients who cannot stop their careers for the duration of time required to undergo microsurgery and subsequent recovery, patients in poor medical health, or for patients who prefer this option for other reasons.

Expectant Management (Observation)
The third option is expectant management, or observation, of the tumor. For patients with small tumors, particularly when they are older, there is a good chance that watching the tumor over time is all that is necessary. If patients select this option, it is important that the rate of tumor growth be determined by performing MRIs every six months and measuring the size of the tumor over time. It is expected that progressive loss of hearing and balance function on that side will occur over time. At any point, the patient may elect microsurgical removal or radiation treatment of the tumor.

Treatment for Potential Residual Effects
Although advances in surgical techniques can help decrease complications and conserve hearing and facial nerve loss, each type of treatment entails some risk of temporary or permanent change in hearing, balance, and facial motion. Treatment options must be individually evaluated for each patient.

The Medical College of Wisconsin Acoustic Neuroma and Skull Base Surgery Program at Froedtert Hospital and the Children's Hospital of Wisconsin offers patients a number of services to ease such side effects. Some patients with hearing loss are candidates for semi-implantable hearing aids. To help patients with facial nerve disorders, the Acoustic Neuroma and Skull Base Surgery Program at Froedtert Hospital offers neuromuscular facial nerve retraining therapy. The Koss Hearing and Balance Center provides advanced diagnostic testing equipment for the assessment of auditory and vestibular function, hearing aids, assistive listening devices, as well as vestibular rehabilitation therapy.

Barbara Abel
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.