Acoustic neuroma is a benign tumor that usually arises from the Schwann cells of the vestibular nerve and in rare cases also from the Schwann cells of the cochlear nerve. The Schwann cells build an electrical insulation layer, enveloping the nerve on the outside. Hence it is also termed vestibular schwannoma.
The acoustic neuroma is a very rare tumor, the incidence of which, however, increases with increasing age. Normally, it grows very slowly. Depending on its localization, two forms of the tumor are distinguished: medial tumor and lateral tumor.
This form of the acoustic neuroma is located in the so-called cerebellopontine angle, which is a very tight space between parts of the cerebellum and the pons. This small niche harbors central parts of many cranial nerves.
An acoustic neuroma growing in this small space can cause certain nerves to be crushed. The result is pressure damage of these nerves. Depending on which nerves are affected, there can be different symptoms present.
This form of the tumor is located in the internal auditory meatus (meatus acusticus internus), which is a canal within the petrous part of the temporal bone. Besides the vestibular and cochlear nerves (nervus vestibulocochlearis), this canal also channels the facial nerve (nervus facialis) and the gustatory nerve (Chorda tympani). Again, the space-occupying growth of the acoustic neuroma can result in pressure damage of nerves and consequently varying symptoms.
A characteristic element of acoustic neuroma is a one-sided onset of symptoms, i.e. only one ear is affected. Basically, there are three very typical symptoms. Therefore, doctors speak of a so-called triad of symptoms. Most of the time, the first sign for the acoustic neuroma is a one-sided loss of hearing. This can either occur suddenly in the form of an acute hearing loss or slowly in the form of worsening hearing impairment. Additionally, acoustic neuroma patients often suffer from ringing in the ears (tinnitus). Moreover, there is usually a dysfunction of the vestibular apparatus and hence dizziness and nystagmus (rapid, involuntary movements of the eye). Occasionally, the acoustic neuroma causes facial pain or numbness in the jaw area.
Possible complications include nausea, vomiting, and movement disorder. These symptoms only appear when the tumor has reached a sizeable mass and begins applying pressure on the brainstem.
Diagram: The location of the tumor on the nerve is such that its weight can prevent the blood supply necessary for proper nerve function (vascular compression).
Generally, the diagnosis can be confirmed by combining three different examination methods:
The hearing evaluation
The hearing evaluation can consist of various methods of testing. On the one hand, we use hearing tests, such as the liminal audiometry test, whereby the patient is exposed to a number of high- and low-pitched tones at varying intensities, respectively. The patient indicates when the tone can be just barely heard. This information is graphed onto a curve of threshold levels. A liminal audiometry for an acoustic neuroma patient deviates downwards at every audio frequency. This is explained by the patient’s increasing loss of hearing. Another very important method of examination is the BERA (Brainstem Evoked Response Audiometry). The patient is connected to an EEG, which measures electrical brain activity. Simultaneously, the patient is exposed to acoustic signals, which in turn trigger changes in the EEG. This examination procedure allows us to determine exactly which part of the acoustic nerve is damaged by the acoustic neuroma. Please note: Due to the lack of specificity of this test, MRI is now used at the “gold standard”, BERA isn’t used anymore.
Examination of the vestibular organ
Acoustic neuroma patients exhibit hypo-excitability in the vestibular organ. Symptoms include dizziness and in some cases rapid, involuntary movements of the eye (nystagmus). This test is only performed if the patient is having nystagmus or dizziness, since that doesn’t occur until the tumor gets really big, this test is not performed unless it is really needed.
Magnetic resonance imaging (MRI)
The MRI is an imaging technique and is used to confirm an acoustic neuroma diagnosis with absolute certainty.
Usually, acoustic neuromas larger than 1 inch in diameter are removed surgically, given the general condition of the patient allows it. If the tumor is smaller than 1 inch, there usually are two different approaches: The first method consists of waiting and regularly monitoring the tumor until it is large enough for surgical removal. The second option is a so-called stereotactic radiosurgery. Hereby the acoustic neuroma is treated with a very high dose of radiation in order to completely destroy it.Get free expert advice