A vestibular schwannoma or acoustic schwannoma is a benign tumor (not a cancer) that most often develops from the two nerves that influence your balance. These 2 nerves connect the inner ear to the brain by passing through a narrow canal located in the petrous bone which is part of the skull base. These tumors therefore arise inside this small bony canal (internal auditory canal) and gradually grow out of this canal towards the brainstem, which is the part of the central nervous system in between the spinal cord and the brain. Once the tumor reaches a certain size, it can compress the brainstem in which passes all the fibers that go from the brain to the spinal cord and vice versa. In the internal auditory canal where these tumors appear, there are 2 other nerves: the auditory nerve (or cochlear nerve) and the facial nerve. These nerves can also be compressed by the tumor.
What are the causes of acoustic neuromas?
These tumors are caused by damage to the genetic material of the Schwann cells covering the vestibular nerve. The reason why this genetic material is damaged is unknown. It is not the result of something you did or bad habits.
This faulty gene is also inherited in neurofibromatosis type 2, a rare disorder that usually involves the growth of tumors on balance nerves on both sides of your head (bilateral vestibular schwannomas).
Neurofibromatosis type 2
The only confirmed risk factor for acoustic neuroma is having a parent with the rare genetic disorder neurofibromatosis type 2. But neurofibromatosis type 2 only accounts for about 5% of acoustic neuroma cases.
A hallmark characteristic of neurofibromatosis type 2 is the development of tumors on the balance nerves on both sides of your head, as well as on other nerves.
Neurofibromatosis type 2 (NF2) is known as an autosomal dominant disorder, meaning that the mutation can be passed on by just one parent (dominant gene). Each child of an affected parent has a 50-50 chance of inheriting it.
What is the frequency of acoustic neuromas?
Acoustic neuromas are very rare. There is one acoustic neuroma diagnosed each year for 100,000 residents. They can occur at all ages, but are most often identified between the ages of 40 and 60.
How fast do acoustic neuromas develop?
Only 40% of vestibular schwannomas increase in size from the time they were identified. If they grow, they generally increase in size slowly with an average of 1-2mm / year, but can sometimes develop faster.
What are the symptoms caused by acoustic neuromas?
The most common symptom is hearing loss. Some patients may lose their hearing completely and sometimes suddenly, but most often they notice a gradual deterioration over time.
Some patients may hear noises or ringing in the ear, called tinnitus. This can be quite annoying and it is difficult to treat but there are a number of effective treatments that can help.
Many patients experience an occasional or persistent unsteadiness, loss of balance.
Other symptoms may occur such as numbness of the face, pain of the bone behind the ear, headache or facial spasms. Facial paralysis and facial asymmetry are unusual.
Are acoustic neuromas dangerous?
Acoustic neuromas are not cancers and do not spread to other areas of the body. If they grow, they do so in a narrow space near the brain and can therefore compress it. If they develop significantly, they can cause more severe disorders or even be life threatening.
How is vestibular schwannoma is diagnosed?
Because symptoms of these tumors resemble other middle and inner ear conditions, they may be difficult to diagnose. Preliminary diagnostic procedures include ear examination and hearing test. Early diagnosis makes the treatment easer.
Hearing test (audiometry): A test which measures how well the patient hears sounds and speech, is usually the first test performed. The patient listens to sounds and speech while wearing earphones attached to a machine that records responses and measures hearing function.
Brainstem auditory evoked response (BAER): This test is performed in some patients to provide information on brain wave activity as a response to clicks or tones. The patient listens to these sounds while wearing electrodes on the scalp and earlobes and earphones. The electrodes pick up and record the brain’s response to these sounds.
Magnetic resonance imaging (MRI): If other tests show that the patient may have acoustic neuroma, MRI is used to confirm the diagnosis. MRI uses magnetic fields and radio waves, rather than x-rays, and computers to create detailed pictures of the brain. If an acoustic neuroma is present, the tumor will appear clearly on the scan. The MRI commonly shows a densely “enhancing” (bright) tumor in the internal auditory canal.
What are the treatments?
There are three main options to treat acoustic neuromas. If the tumor is small, it is most often preferable to observe. This has no potential side effects unlike other treatment options, but periodic monitoring is necessary to make sure the tumor does not grow. An MRI every year is usually scheduled. If the tumor grows or if the symptoms become bothersome, then active treatment is recommended.
The treatments are surgery and radiotherapy. The choice between the two techniques is not always easy and a detailed discussion with your surgeon will allow you to understand the advantages and disadvantages of each technique and to make the best decision with him.
Surgery is an effective treatment generally reserved for tumors that already have a certain size and for which radiotherapy is not possible. However, the operation is a delicate procedure with a risk of damaging the facial nerve. This results in weakness of the face on the side of the tumor. The risk varies depending on the size of the tumor. Other less common complications can occur after surgery. Very often, at the time of the surgical intervention, hearing is already diminished or even greatly diminished. It is often no longer “useful” because it is dominated by hearing on the opposite side. The chances of keeping hearing when it is already impaired pre-operatively are very low , but the post-operative inconfort caused by this loss is usually limited. f hearing is intact before the surgery, there is a good chance of keeping a useful hearing depending on the size of the tumor.
The philosophy of our team for the surgical treatment of these tumors is to favor the function of the facial nerve even if it means leaving a tumor residue on the facial nerve. This occurs in approximately 30 to 40% of our interventions. For the majority of those, this residue does not change over time. In this case growth, radiosurgery is generally offered with excellent results considering the small size of the residue.
Radiation therapy is an effective treatment which is preferentially intended for small and medium-sized tumors. The radiotherapy technique generally proposed for acoustic neuromas is called radiosurgery. This consists in delivering an important dose of radiation to the tumor in 1 or 3 fractions, using multiple beams which converge at the level of the lesion, with very high ballistic precision. This does not remove the lesion but stops the progression of the tumor. In about 5% of cases, the tumor continues to grow despite this treatment. In this case it can be necessary to perform.
Multidisciplinary vestibular schwannoma group
All the teams involved in the management of these tumors (neurosurgeon, ENT surgeons, radiotherapists, neuroradiologists) meet once a month in the neurosurgery department to discuss the files of patients with neuromas and together define the best strategy for a given patient: Surgery, radiotherapy, monitoring.