Acoustic Neuroma (Vestibular Schwannoma)
What Is It?
An acoustic neuroma is a specific type of tumor that occurs adjacent to the brain stem. Although the term acoustic neuroma is still frequently used, the more appropriate name for the tumor is a vestibular schwannoma. It is typically a benign tumor which arises from Schwann cells on the cranial nerve bringing balance information from inner ear back to the brain stem, the vestibular component of the vestibulocochlear nerve (8th cranial nerve). Although schwannomas
in general can occur on virtually any peripheral nerve, this vestibular nerve tumor is one of the most common forms.
Although this type of tumor is technically a peripheral nerve tumor, it is often referred to as a brain tumor because of its close approximation to the base of the brain. Vestibular schwannomas are also sometimes referred to as a skull base tumor because they occur at the base of the skull, adjacent to the temporal bone and the inner ear.
These tumors typically begin growing in the internal auditory canal, the opening in the bone through which the nerves travel from the inner ear to the brain stem. As they enlarge they can grow out of the canal into the space adjacent to the brain stem and can eventually put pressure on the brain stem itself when large enough.
Although acoustic neuroma is relatively uncommon in the general population, there is a genetic disorder which greatly increases the risk for this tumor as well as others. Neurofibromatosis type 2 (NF 2) is a genetic disorder caused by a mutation of a specific gene. Individuals with the mutated gene have a tendency to develop schwannomas as well as some other types of tumors. In these patients, bilateral vestibular schwannomas (occuring on both sides) is not uncommon.
What Types of Symptoms Are Typical?
As an acoustic neuroma grows on the vestibular nerve it causes damage to the nerve and can cause vertigo and/or dizziness. Additionally, because of pressure on the adjacent cochlear nerve, which brings hearing sensation to the brain from the inner ear, most patients experience unilateral hearing loss and/or tinnitus (ringing) in that ear. The hearing loss and tinnitus only involve one ear. The hearing loss is gradual and usually involves higher frequencies first. Patients often complain that they first notice a problem understanding voices when trying to talk on the phone with that ear. Unilateral hearing loss, dizziness and tinnitus are the most common presenting symptoms.
As the tumor enlarges it can cause additional symptoms. Headache is not uncommon. Compression of the adjacent facial nerve can cause weakness on that side of the face. As the tumor gets very large it can compress the brain stem and cause many other symptoms and can even cause obstructive hydrocephalus which can be life-threatening. However, these tumors tend to be rather slow growing so the progression of these symptoms generally occur over months to years.
How Is The Diagnosis Typically Made?
Unilateral hearing loss, tinnitus and/or dizziness are usually worked up with a thorough ear examination and testing called audiometry. The audiogram evaluates the hearing and can demonstrate the severity and type of hearing loss. These patients will also typically undergo an imaging study, most frequently an MRI
, to identify the tumor. The typical location and appearance of this tumor make its diagnosis on MRI typically straightforward. However, to positively identify the tumor as a schwannoma and rule out other types of tumors a piece of the tumor (a biopsy) is needed to be evaluated by a pathologist.
What Are Some Common Treatments?
The earlier these tumors are diagnosed and treated, the better the outcome, typically. While some patients and their physicians may choose to simply wait and observe the tumor with serial MRIs if the tumor is very small and causing minimal symptoms, most patients will decide to undergo some type of treatment of the tumor. Traditionally, the treatment offered is a surgery to remove the tumor. There are various types of surgical procedures which can be performed depending on the tumor size, symptoms and surgeon preference. The goal is generally to remove as much of the tumor as possible. If the complete tumor is removed, the risk of recurrence for these benign masses is generally very low.
Because of the close proximity of these tumors to the facial nerve, which supplies the muscles of the face, injury to the facial nerve is one of the most important complications which can occur with these procedures. While in most cases the nerve can be identified and protected, in a small number of cases the nerve is injured and can result in a transient or permanent facial weakness (palsy) on that side of the face.
Another option for treatment of some acoustic neuromas is radiosurgery with focused-beam radiation. The goal is to irradiate the tumor with high energy radiation to kill the dividing cells. This treatment avoids a surgery but generally does not result in the tumor disappearing completely. However, it often slows or halts the growth of the tumor and in some cases the tumor will shrink after treatment. This is sometimes considered as a primary treatment of the tumor, particularly for small tumors. However, it is also considered for treating recurrent or residual tumors after prior surgical treatment. If an acoustic neuroma is treated with radiation or there is a residual left behind after surgery, these patients generally require long-term follow-up with occasional MRI scans to track the progression of the tumor.
The ideal management and treatment of these tumors vary depending on the specifics of each case. Each patient should discuss their options with their own treating physicians.
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This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.