Acoustic Neuroma

Acoustic neuromas, also known as vestibular schwannomas, are a noncancerous and usually slow-growing tumor that develops on the main (vestibular) nerves leading from your inner ear to your brain. Branches of the 2 vestibular nerves directly influence your balance and hearing; pressure from an acoustic neuroma can cause hearing loss, ringing in your ear (tinnitus), and unsteadiness.

Acoustic neuromas arise from the Schwann cells covering the nerves and typically grow slowly. Rarely, these tumors may grow rapidly and become large enough to press against the brain and interfere with vital functions.

The cause of acoustic neuromas is not well understood. For most acoustic neuromas, the cause at the level of the cellular machinery is the failure of a “governor” gene to exert its effect in suppressing the growth of Schwann cells—those cells responsible for coating nerve fibers with insulation. The result is “wart-like” growth of these cells to produce the neuroma (or more precisely, schwannoma).

The only environmental exposure that has been definitively associated with an increased incidence is radiation exposure to the head. While studying the association between cell phone use and the development of these tumors is difficult, the scientific community does not generally accept that any relationship has been proven.

For the most part it is not an inherited disease; however, 5% of cases are associated with a genetic disorder called neurofibromatosis type 2. These individuals demonstrate two-sided (I.e., bilateral) vestibular tumors often associated with other tumors around the brain and/or in the spine. The vast majority of acoustic neuromas are unilateral (one-sided) and sporadic (nonhereditary).

Unilateral (one side) occurs spontaneously without any evidence of family history, accounts for 95% of acoustic neuromas

Bilateral (both sides) is most likely caused by a genetic condition called Neurofibromatosis Type 2 (NF2) which affects approximately 1 in every 40,000 people. NF2 will be suspected if a parent/sibling/child of the patient has NF2 and the acoustic neuroma occurs before age 30 or if the patient has had a meningioma, glioma, or cataract.

Most recent publications suggest that the incidence of acoustic neuromas is rising. This is partly because of advances in MRI scanning as well as patient life-expectancy being in the 70s-80s.  It is estimated that the incidence of acoustic neuroma in the general population is between 1 to 3.5 in every 100,000.

Common signs and symptoms of acoustic neuromas include:

• Hearing loss, usually gradual — although in some cases sudden — and occurring on only one side or more pronounced on one side
• Ringing (tinnitus) in the affected ear
• Unsteadiness, loss of balance
• Dizziness (vertigo)
• Facial numbness and ,rarely, weakness of facial movement (facial palsy)

In rare cases, an acoustic neuroma may grow large enough to compress the brainstem and become life-threatening.

Symptoms are usually associated with the size of the tumors, but this is not always consistent. Many patients experience few symptoms despite the presence of a large tumors. Small tumors are defined at 2 cm or less, medium tumors are between 2 and 4 cm, and large tumors are over 4 cm. Smaller tumors can often be associated with few symptoms, whereas large compressive tumors can be life threatening.

Doctors usually take a complete health history. They will also ask about recent symptoms and past health conditions, including a family health history. A complete physical exam will be done, including an examine of hearing and the nervous system. Your doctor may ask you (or your child) to do simple things like walk, touch your finger to your nose, hold your hands out, or follow a light with your eyes. If a doctor thinks you may have a brain tumor, imaging tests of the brain will be needed

Acoustic neuromas are often difficult to diagnose in the early stages because signs and symptoms may be subtle and develop gradually over time. Common symptoms such as hearing loss are also associated with many other middle and inner ear problems.

After asking questions about your symptoms, your doctor will conduct an ear exam. Your doctor will typically order the following tests:

• Hearing test (audiometry). In this test, conducted by a hearing specialist (audiologist), the patient hears sounds directed to one ear at a time. The audiologist presents a range of sounds of various tones and asks the patient to indicate each time he/she hears the sound. Each tone is repeated at faint levels to find out when one can barely hear.
  
  The audiologist also presents various words to determine speech clarity (also known as the word recognition score)

• Imaging. Magnetic resonance imaging (MRI) is the preferred imaging test to confirm the presence of acoustic neuroma and can detect tumors as small as 1 to 2 millimeters in diameter. If MRI is unavailable or you can't tolerate an MRI scan, computerized tomography (CT Scan) may be used, but it may miss small tumors

A patient may first see the primary healthcare provider for an acoustic neuroma. He/she may refer the patient to a doctor that deals with brain tumors.  As most patients with acoustic neuromas have hearing loss, the first person consulted is an otolaryngologist (ENT). If a tumor is diagnosed, the patient is then referred to:

          Neurotologist / skull base surgeon: This is a surgeon who specializes in the treatment of diseases and tumors of the ear/temporal bone.

• Neurologist. This specialist diagnoses and treats brain and spinal cord diseases.
• Neurosurgeon. This is a specialist who does brain or spinal cord surgery and works with the neurotologist.

Acoustic neuroma treatment may vary, depending on the size and growth of the acoustic neuroma, the patient’s overall health, and if the patient is experiencing symptoms. To treat an acoustic neuroma, your doctor may suggest one or more of three potential treatment methods: monitoring (observation), surgery, or radiation therapy.

Monitoring

If you have a small acoustic neuroma that isn't growing or is growing slowly and causes few or no signs or symptoms, the physician may decide to monitor it, especially if the patient is an older adult or otherwise not a good candidate for surgery.

The physician may recommend that the patient have regular imaging and hearing tests, usually every six to 12 months, to determine whether the tumor is growing and how quickly. If the scans show the tumor is growing or if the tumor causes progressive symptoms or other difficulties, the patient may need to undergo treatment.

Surgery

The physician may recommend surgery to remove an acoustic neuroma. The surgeon may use one of several techniques for removing an acoustic neuroma, depending on the size of the tumor, hearing status, and other factors.

The goal of surgery is to remove the tumor, preserve the facial nerve to prevent facial paralysis, and preserve hearing, if and when possible.

Surgery for an acoustic neuroma is performed under general anesthesia and involves removing the tumor through the inner ear or through a window in the skull.

The entire tumor may not be able to be completely removed in certain cases (also known as subtotal or near-total resection). For example, this may happen if the tumor is too close to important parts of the brain or the facial nerve.

Rarely, surgical removal of the tumor may worsen symptoms.

• Complications may include:
• Leakage of cerebrospinal fluid through the wound
• Hearing loss
• Facial weakness
• Facial numbness
• Ringing in the ear
• Balance problems
• Persistent headache
• Infection of the cerebrospinal fluid (meningitis)
• Stroke or brain bleeding

In experienced hands, the risk of a major complication is <1%.

• Radiation therapy
• Gamma Knife stereotactic radiosurgery

Stereotactic radiosurgery. The doctor may recommend a type of radiation therapy known as stereotactic radiosurgery.  The physician may refer the patient to see a radiation oncologist for a 2nd opinion.  Radiosurgery is more commonly used in patients who are elderly or if the patient has too many medical problems to undergo surgery safely.

Stereotactic radiosurgery, such as Gamma Knife, Cyberknife, or Linac radiosurgery, uses many tiny gamma rays to deliver a precisely targeted dose of radiation to a tumor while minimizing damage to the surrounding tissue. Using imaging scans (e.g., the MRI and CT), the radiation oncologist pinpoints the tumor and then plans where to direct the radiation beams.

The radiation oncologist attaches a lightweight head frame to the scalp, which has been numbed, to keep the head still during the procedure.

The goal of stereotactic radiosurgery is to stop the growth of a tumor by reducing the blood-supply to the tumor

It may take weeks, months or years before the effects of radiosurgery become evident. The radiation oncologist, in conjunction with the neurotologist, will monitor progress with follow-up imaging studies and hearing tests.

Risks of radiosurgery include hearing loss, ringing in the ear, facial weakness, facial numbness, balance problems, treatment failure (continued tumor growth), and rare risk of malignant transformation (whereby the tumor goes from a benign to malignant state).

Stereotactic radiotherapy. Fractionated stereotactic radiotherapy (SRT) delivers a small dose of radiation to the tumor over several sessions in an effort to curb the growth of the tumor without damaging surrounding brain tissue.

Proton beam therapy. This type of radiation therapy uses high-energy beams of positively charged particles called protons that are delivered to the affected area in targeted doses to treat tumors and minimize radiation exposure to the surrounding area.

Supportive therapy

In addition to treatment to remove or stop the growth of the tumor, the physician may recommend supportive therapies to address symptoms or complications of an acoustic neuroma and its treatment, such as hearing loss, tinnitus, dizziness, or balance problems.

Hearing aids and cochlear implants or other treatments may also be recommended to treat hearing loss.

Recurrence of acoustic neuromas can be caused by several factors and usually only occur in a small percentage of patients. There is, unfortunately, no good way to predict which tumors will recur after treatment. Sometimes, a small part of the tumor is left along the facial nerve at the time of initial surgery in an effort to preserve facial function. Management options for the recurrence or re-growth of the tumors can include revision surgery or radiation. Each patient should be counseled on a case-by-case basis by doctors with expertise and experience with treating acoustic neuromas

Balance

Balance and dizziness issues are common with in patients with acoustic neuromas, both pre- and post-treatment as well as during observation (wait and scan method). These symptoms are usually short-term and can improve with rehabilitation and a daily exercise regimen. Some patients experience vertigo or nausea. These symptoms can be mild to severe and may be noticeable only during certain activities; they can rarely impact the ability to work or drive. The location of the tumors and the size of the tumors affect balance and the amount of residual vestibular/balance function on the side of the tumor.

Acoustic neuromas are also called vestibular schwannomas because they arise from the sheath of the eighth cranial nerve, which plays an important role in the body's balance system. With observation, surgery, or radiation the balance nerve may be compromised. Balance (vestibular) physical therapy can be quite effective for many acoustic neuroma patients

CSF leak

Cerebrospinal fluid, or CSF, is a watery fluid that flows in the ventricles (cavities) within the brain and around the surface of the brain and spinal cord. CSF is continuously produced and absorbed. On occasion, CSF leaks can happen after the microsurgical removal of an acoustic neuroma. The leak can occur either through the nose, ear, or from the incision. Such leaks appear as a clear, watery discharge and can leave a salty taste in the patient’s mouth or a dripping feeling from the nose or from the incision. If left untreated, an infection that could lead to meningitis may follow; therefore, these symptoms should be reported to the doctor/surgeon immediately.

Eye Problems

Because of potential involvement of an acoustic neuroma with the trigeminal (sensation) nerve and facial movement nerve (facial nerve), acoustic neuroma patients may have problems with their eyes. The two nerves discussed above can affect blinking and eyelid closure, sensation, and tear production.

Acoustic neuroma patients may experience difficulty blinking, excess moisture or dryness, double vision, or eye sensitivity. It is important that the eye be artificially protected (e..g, with a moisture chamber); it may be necessary to apply artificial tears or eye ointment. There are also several surgical options for improving eye issues

Facial Weakness

Acoustic neuroma patients can experience facial weakness or complete paralysis, either before or after treatment. Post-surgery facial paralysis is less common than it used to be because of advances in surgical techniques and intraoperative monitoring.

The 7th cranial nerve, or facial nerve, is often affected in the treatment of an acoustic neuroma. The nerve may be damaged with either surgery or radiation; however, it is usually possible to preserve some degree of facial function, even in cases where the nerve is extensively involved. Temporary weakness of the face due to nerve swelling is common; in some cases, there may be permanent facial weakness.

If the facial nerve is damaged, it is possible for it to regenerate slowly. It is also possible to reconnect the facial nerve during or after surgery. When it is not possible to repair the facial nerve, additional surgeries may be necessary to substitute other nerves, allowing partial voluntary movement to return. There are also many non-surgical options including facial rehabilitation exercises for patients with facial palsy.

Hearing loss

Hearing loss in acoustic neuroma patients can vary from no or mild hearing loss to complete deafness (also known as profound hearing loss or single-sided deafness – SSD). Hearing loss on one side (asymmetric) is the most common first symptom and indication of an acoustic neuroma. According to the 2014 ANA Patient Survey, 86% of participants reported single-sided hearing loss or deafness. Most patients present with a slowly progressive hearing loss; however, some patients experience a sudden loss of hearing on the side of the tumor. Tinnitus on the tumor side is also common. An audiologist will look for asymmetrical hearing loss, particularly high-frequency sensorineural hearing loss. 

Hearing loss may occur whether one chooses observation, radiation therapy, or surgery. Patients and their doctors should discuss the possibility of hearing preservation with each treatment option. There are many options for hearing aids, each with pros and cons. As the degree of hearing loss varies among patients, the type of hearing aid best-suited for each depends on many factors.

Hearing loss can disrupt one’s social and work life; it can contribute to depression and a sense of isolation. Hearing rehabilitation by using hearing aids and assistive listening devices, can be quite useful and improve quality of life.  In addition, there is now evidence that treating hearing loss may reduce the risk of cognitive decline and dementia with aging.