Acoustic neuroma is the most common type of brain tumor. It is non-cancerous and grows on a tiny nerve that is located near facial nerves between the inner ear and brainstem. An acoustic neuroma occurs on the eighth cranial nerve. It consists of three nerves that link the eardrum to the brain, including the cochlear nerve (carries hearing information) and left and right nerves (carry balance signals from the inner ear to the brain). Schwann cells (neurilemma cells) protect these nerves. However, an acoustic neuroma causes a tumor to grow on Schwann cells. And if the tumor persists, it will compress the brainstem. Thus, an acoustic neuroma can be life-threatening.
Acoustic neuromas are rarely inherited from a parent. However, an acoustic neuroma caused by neurofibromatosis type II (NF 2) is more common in young patients and those with a family history of neural tumors.
Acoustic Neuroma Association – What is an Acoustic Neuroma?
How Common Are Acoustic Neuromas?
The National Institutes of Health (NIH) has performed a variety of acoustic neuroma and acoustic neuroma facial paralysis studies, and some of their study findings include:
- Acoustic neuromas comprise roughly 6 percent of all intracranial tumors, 30 percent of brainstem tumors and 85 percent of tumors in the cerebellopontine angle (CPA) region of the brain.
- 10 percent of acoustic neuromas are meningiomas (non-cancerous tumors that surround the brain and spinal cord).
- Only about one out of every 100,000 acoustic neuromas are diagnosed annually in the United States.
- Each year, there are roughly 2,000 to 3,000 new acoustic neuroma cases reported in the United States.
- Among patients who suffer from hearing asymmetry, only about one in 1,000 is dealing with an acoustic neuroma.
The treatment approach to facial paralysis in this patient population depends on the intraoperative surgical findings. A conservative approach is prudent if the surgeon who performs the acoustic neuroma feels that the nerve was saved during the operation. Patients will often require eye care and temporary measures such as suture suspensions to prevent unwanted complications and improve oral issues. The risk of facial paralysis with acoustic neuroma surgery is between 4-15%. Tumor size, surgeon experience and approach for surgery are important factors.
Acoustic Neuroma & Facial Paralysis Symptoms
More than 95 percent of acoustic neuroma patients suffer hearing loss. In addition, roughly 90 percent of acoustic neuroma patients encounter a gradual, one-side hearing impairment. Among patients who suffer a hearing impairment due to acoustic neuroma, nearly two-thirds deal with a high-frequency sensorineural pattern. Meanwhile, the remainder frequently suffer from low-frequency hearing loss, i.e. a form of Meniere’s disease.
In some instances, acoustic neuroma patients deal with “cookie bite” pattern, an indication of congenital hearing loss. Sudden hearing loss also occurs among 25 percent of acoustic neuroma patients but is rarely attributed directly to acoustic neuroma. Conversely, sudden hearing loss is attributed to an acoustic neuroma patient only about 1 percent to 5 percent of the time, as there are many causes of sudden hearing loss. Furthermore, hearing remains normal in about 11 percent of acoustic neuroma patients. Tinnitus (perception of noise ringing in the ears) also may be attributed to acoustic neuroma; it often is unilateral and confined to the affected ear.
Due in part to the origin of acoustics in the vestibular nerve, about 20 percent of acoustic neuroma patients will experience vertigo. In many cases, vertigo is more common in patients with smaller tumors than larger ones. Meanwhile, a lack of balance affects approximately 70 percent of acoustic neuroma patients who experience vertigo. Most of these patients will have large tumors. Loss of use of one or more of the arms and legs may occur but are unusual.
Acoustic neuroma facial paralysis may occur if a large tumor is present. In some situations, carbamazepine medication for neuralgia may enable a patient to limit acoustic neuroma facial nerve damage. An acoustic neuroma patient also may experience headaches if he or she is dealing with a large tumor.
If the nerve was cut intraoperatively or if the facial palsy does not resolve, then a more active approach must be taken. Definitive eyelid reconstruction with gold weight or palpebral spring must be considered. Facial reanimation as discussed in other sections of this web site must then be utilized. The following section is a more detailed discussion about acoustic neuroma.
A hearing test, also known as conventional audiometry, is used as a diagnostic test for acoustic neuroma. Testing such as auditory gadolinium enhanced magnetic resonance imaging, can establish the diagnosis. A new technique called “Auditory Brainstem Response” testing is less sensitive than enhanced magnetic resonance imaging (MRI), but it is considerably less expensive.
When is it time to consider facial reanimation after acoustic neuroma surgery?
View Dr. Azizzadeh’s presentation for the Acoustic Neuroma Association on facial paralysis treatment options following acoustic neuroma surgery. Dr. Azizzadeh discusses all of the current facial reanimation treatment options, including the management of partial paralysis and synkinesis.
Treatment Options for Acoustic Neuroma
There are four distinct treatment options for an acoustic neuroma:
- Medical treatment or taking a “wait and see” approach (conservative management)
- Acoustic neuroma removal surgery
- Gamma-knife radiosurgery
- Cochlear implantation
Roughly 25 percent of acoustic neuromas are treated with medical management, which consists of:
- Periodic monitoring of the patient’s neurological status
- Use of hearing aids when appropriate
- Periodic imaging studies
Acoustic neuromas develop slowly, and there are no current medications that have been shown to limit acoustic neuroma growth. A patient may use serial audiometry and/or MRI scans to track an acoustic neuroma. After an acoustic neuroma is diagnosed, an MRI may be obtained at six months, followed by annual MRIs.
The threat of acoustic neuroma can decline based on an individual’s age. For example, an older acoustic neuroma patient may continue to take his or her current medications. In this instance, the acoustic neuroma may be unlikely to impact the patient’s expected lifespan.
Like any surgery, there are risks associated with an acoustic neuroma procedure. An MRI sometimes is unable to show how quickly an acoustic neuroma is growing, and the tumor could cause a patient to suffer hearing loss. If this happens, a patient may no longer be a viable candidate for a hearing preservation procedure.
A recent study indicated that roughly 10 percent to 43 percent of acoustic neuroma patients who were evaluated for about two years lost “useful” hearing. Typically, 75 percent of acoustic neuromas will display visible growth of approximately 1.5 mm over the course of one year. Keep in mind, however, that some acoustic neuromas will grow faster than others.
Possible Damage and Rehabilitation
For those diagnosed with an acoustic neuroma, there are many aspects of treatment. In this article, Dr. Azizzadeh discusses the nuances of treating an acoustic neuroma while preserving facial nerve function.
Acoustic Neuroma Surgery
Currently, about 50 percent of acoustic neuromas receive surgical treatment. Acoustic neuroma surgery often is a preferred choice for patients because it may prevent fatal complications associated with tumor growth and help an individual preserve his or hearing. The surgery usually is performed by a neurotologist (specialized otolaryngologist), neurosurgeon and other surgeons at an academic center.
There are several types of acoustic neuroma procedures:
- Retrosigmoid/Suboccipital: Serves as a posterior approach that involves acoustic neuroma removal through the skull.
- Translabyrinthine: Involves acoustic neuroma removal through the inner ear, commonly resulting in hearing loss.
- Middle Fossa: Offers acoustic neuroma removal through the skull, improving a patient’s chances of preserving his or her hearing.
Each acoustic neuroma surgery offers pros and cons, and an acoustic neuroma patient should assess each type of procedure closely. By doing so, an acoustic neuroma patient will be able to make an informed surgery decision based on his or her individual needs.
An acoustic neuroma patient will be admitted to the hospital the day before surgery and recover in a monitored hospital unit after surgery. In most cases, an acoustic neuroma patient will be discharged within four to six days of surgery and can return to work in approximately six weeks. Also, MRIs may be performed for one to five years after surgery to identify a residual or recurrent tumor, according to the American Hearing Research Foundation.
Conventional audiometry may be used as part of an acoustic neuroma treatment. It may lead to further testing, such as auditory brainstem response (ABR) testing and gadolinium enhanced MRIs.
MRIs usually offer more accurate results than ABR testing. Comparatively, ABR testing may prove to be a more cost-effective option than MRIs. A new technique, summated ABR, is now available and combines several ABRs over time. Summated ABR may provide a superior alternative to traditional ABR testing.
Electronystagmography (ENG testing) is rarely used to address acoustic neuroma, as nearly half of all tumors are linked to unilateral loss of calorics. ENG testing is not specific, and as such, may lead to inaccurate results. Also, rotatory chair testing is less sensitive than caloric testing, and posturography is insensitive to acoustic neuroma.
A gadolinium enhanced T1 MRI represents the ideal test for excluding an acoustic neuroma, but it can be more expensive than audiometry and ABR testing. This MRI can be used to enhance an acoustic neuroma and expand the internal auditory meatus for advanced evaluation.
On the other hand, a fast spin-echo T2 variant of MRI is sensitive to acoustics but may serve as a cost-effective option in clinical settings. Or, if an MRI cannot be completed, an air-CT scan may provide a valuable alternative. The air-CT scan is optimal for high-risk individuals, particularly if ABR testing indicates an acoustic neuroma may be present.
Acoustic neuromas are classified by their size and location. An acoustic neuroma may reach up to 4 cm in size, and the size classifications of acoustic neuromas are:
- Intracanalicular: Measured in millimeters
- Small: Less than 1.5 cm
- Moderate: Ranges from 1.5 cm to 3 cm
- Large: 3 cm or greater
An intracanalicular acoustic neuroma is located in the internal auditory canal (IAC). A cisternal tumor extends outside the IAC, while a compressive tumor touches the cerebellum or brainstem. And in some instances, tumors may obstruct cerebrospinal fluid drainage pathways in the fourth ventricle.
If you are suffering from facial paralysis or any other related condition, schedule a consultation with Dr. Azizzadeh by calling (310) 657-2203 today.
The Facial Paralysis Institute and Dr. Babak Azizzadeh are honored to be a Silver Sponsor for the Acoustic Neuroma Association. ANA aims to advance acoustic neuroma education and support, as well as increase overall acoustic neuroma awareness. Click here to learn more: https://www.anausa.org/
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