Ear Center: Acoustic Neuroma
Acoustic Neuroma (AN) (also Vestibular Schwannoma)
Acoustic neuroma (AN), also called vestibular schwannoma, is a benign non-cancerous tumor that originates from the vestibular nerve ("the balance nerve") that supplies the inner ear. In reality, the tumor develops from the cells that wrap around the nerve (the Schwann cells), not from the nerve itself. Most acoustic neuromas arise from within the internal auditory canal (the bony canal that connects the inner ear to the brainstem), but some tumors have been found to originate from the cerebellopontine angle at the entrance of the internal auditory canal (i.e. closer to the brainstem). The tumor is usually slow growing at a rate of 1-2 mm per year, often taking many years to become large enough to cause any symptoms. However, some tumors with higher growth rate have been reported. The reported incidence of acoustic neuroma is approximately 10 per million per year. It has no significant racial predilection. It appears that women are more affected than men, although not to a substantial degree. Acoustic neuroma are most likely diagnosed between ages 30 and 60. It is rare in children.
There are two general forms of acoustic neuroma:
- the more common sporadic form
- those associated with NF2 (neurofibromatosis type 2).
The sporadic tumors are one-sided and comprise approximately 95% of the AN cases. NF-2 associated tumors are usually bilateral and account for the remaining 5%. Approximately half of the NF-2 patients inherit the disorder from an affected parent, and the other half may half the mutation for the first time. Unlike patients with the sporadic form of AN, patients with NF2 typically develop the tumors early in life (teens or early childhood), and they usually also develop multiple other brain and spinal cord tumors.
Most of the symptoms of acoustic neuroma are due to the tumor pressing on the adjacent cranial nerves. The internal auditory canal houses the vestibular nerve, the auditory nerve ("the hearing nerve"), and the facial nerve ("the nerve that moves the facial muscles"). As the tumor enlarges, it first presses against the vestibular and the auditory nerves, typically causing one-sided hearing loss, ringing in the ear, and/or dizziness. The larger tumor may also compress the facial nerve, causing one-sided facial weakness or paralysis of the facial muscles. If the tumor becomes very large, it will press against other lower cranial nerves, the brainstem, and the cerebellum, eventually becoming life-threatening.
Since most small acoustic neuromas are asymptomatic, early detection is often difficult. When the early symptoms of one-sided hearing loss, ringing in the ear, dizziness, and/or loss of balance first appear, it is recommended that the patient be evaluated by an otologist (an ear doctor). A thorough physical examination and hearing/vestibular testing may suggest the diagnosis of acoustic neuroma. An imaging study is usually needed for definitive diagnosis. Currently, magnetic resonance imaging (MRI) with IV contrast is the most sensitive modality for diagnosing an acoustic neuroma. MRI with contrast is able to detect an acoustic neuroma as small as 1mm in diameter. For patients unable to undergo MRI testing, high resolution CT scan with IV contrast can be used. However, CT scan may overlook some of the smaller tumors (< 1cm).
Three options are currently available for managing acoustic neuroma:
- conservative observation ("watch & wait")
- surgery (three different approaches)
- radiation therapy (stereotactic, gamma knife radiosurgery)
Conservative Observation: Conservative treatment is often recommended for patients who are elderly, in poor health, or who otherwise are not good candidates for surgical or radiation treatment. Conservative observation is also appropriate for patients with small tumors that are not growing or are growing slowly and not causing significant symptoms. Consultation with your physician is needed to determine if conservative observation is appropriate. Regular MRI head scans with constrast will be needed to determine the status and growth rate of the tumor.
Recent information concerning "watch & wait" has been reported from Denmark. All patients who are diagnosed with acoustic neuromas in Denmark are referred to and treated in one hospital in Copenhagen. They now have data on over 2,000 patients with acoustic neuromas. Patients who present with 100% word recognition in the affected ear will maintain their hearing over a 5 year period. Other patients with less than 100% word recognition will go on to lose hearing over a 5 year period.
In the United States, there is a general trend away from surgery for older patients with small tumors. More tumors are being discovered at a smaller size due to the increased availability and use of MRI imaging.
Surgery: Currently, the only treatment that can cure the patient is surgical removal of the tumor. Surgery is usually recommended for younger patients, patients with larger tumors, and those without useful hearing. Surgery for acoustic neuroma is performed under general anesthesia using an operating microscope and finely scaled instruments. The surgery is typically performed by a team of surgeons that includes an otologist/neurotologist and a neurosurgeon. Depending on the size/location of the tumor and the hearing level of the affected ear, three different approaches are available for tumor removal:
- translabyrinthine (behind the ear and through the mastoid and inner ear; results in total loss of hearing)
- retrosigmoid (behind the ear in the occipital area)
- middle fossa (above the ear through the temporal area)
There are advantages and disadvantages of each approach.
Translabyrinthine approach is commonly used when the patient has significantly reduced hearing in the affected ear. This approach is performed by making an incision behind the ear, and removing the bone behind the ear canal and around the inner ear. A craniotomy is avoided, and minimal brain retraction is needed using this approach. The main advantage of the translabyrinthine approach is lesser morbidity and faster recovery after the surgery. This is most notable in the reduced incidence of persistent post-craniotomy headaches. The main disadvantage of this approach is the complete loss of hearing. This approach requires the removal of part of the inner ear, necessitating the sacrifice of hearing in the affected ear.
The retrosigmoid and middle fossa approaches require a craniotomy and retraction of brain tissue in order to expose and remove the tumor. They both have the advantage of potentially saving the residual hearing in the affected ear. The down sides are typically related to the need for craniotomy and brain retraction, often with longer post-op recovery course. The specifics, risks, benefits, alternatives, and details of the surgery should be reviewed with your surgeons before a particular approach is chosen.
Gamma Knife: As an alternative to surgery, radiation therapy (also called "gamma knife" radiosurgery) may be used to treat acoustic neuroma. Radiation therapy does not remove the tumor. Rather, it limits the growth, or in some cases, it reduces the size of the tumor. The treatment can usually be completed in one day. It is sometimes the preferred option for patients who are poor surgical candidates, such as patients with advanced age, preexisting health problems, bilateral tumors, or tumor in the only hearing ear. Gamma knife is usually not recommended for young patients as the long-term effects of the radiation are not fully known. Levels of radiation may be in the 12-12.5 Gy range (11-13 Gy).
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Dr. Kraus is available to discuss further aspects of the treatment and management of acoustic neuromas (vestibular schwannomas) although he does not perform the operations in Greensboro.
Updated November 25, 2012