What is Schwannoma of the auditory nerve?
Auditory nerve schwannoma (vestibular schwannoma, vestibulocochlear schwannoma, n. Vestibulocochlear schwannoma, neurinoma) is a benign and most often slow growing tumor that develops from the auditory and equilibrium nerve (nerve VIII). Tumor-induced changes and pressure on healthy parts of the nerve can cause gradual hearing worsening and loss, tinnitus and disturbances in balance.
This tumor of nerve VIII, according to its name, develops from Schwann cells, which form the outer layer of this nerve. It can grow very slowly (1- 1.5mm / year) or it may stop at some point. It should be noted that at this site 25-30mm tumor is considered to be relatively large. In rare cases, schwannoma of the auditory nerve can grow very rapidly, which in turn can lead to disturbances in the proximity of the brainstem and various vital functions.
What are the symptoms of vestibulocochlear schwannoma?
Initial signs of the disease can often be difficult to spot and may develop very gradually over many years. These symptoms most often develop from tumor-induced changes in the auditory and balance nerves. Occasionally, the tumor can cause imprinting of a nearby nerve (facial nerve, trigeminal nerve) or brainstem, and other very serious health problems not related to hearing and balance.
The most common signs of vestibular neuroma are:
- Unilateral (in rare cases bilateral) progressive hearing worsening or loss;
- Noise (Tinnitus) on the diseased side;
- Dizziness and balance disorders;
- Facial numbness;
- Very rare weakness of the facial muscles or hemifacial spasm (unilateral facial twitching of the facial muscles).
Why vestibular neurinoma can occur?
One of the causes of this tumor could be a defect in one gene on chromosome 22. Normally, this gene produces a tumor suppressor protein. This protein, in turn, helps control the growth of Schwann cells in the nerve sheath.
This gene defect can be inherited from a genetic disorder called neurofibrimatosis type 2. It is a relatively rare disease that can cause bilateral tumors of the auditory nerve (bilateral vestibulocochlear schwannomas).
Neurofibromatosis type 2 (NF2)
Neurofibrimatosis type 2, also known as NF2, is a genetically inherited (autosomal dominant) disease characterized by benign nerve tumors. These can be bilateral schwannomas of the genital nerve or neurinomas of other body nerves. Only a few percent of vestibular cohort schwanoma cases are related to NF2.
Neurofibrimatosis type 2 is known as an autosomal dominant disease. Every child of a sick parent has a 50:50 chance of developing the disease.
What type of examinations can help diagnose the auditory nerve neurinoma?
The early detection of these cancers is often quite difficult because the signs and symptoms of the disease develop very gradually and are common to many other diseases of the inner ear and middle ear.
With complaints of hearing problems and / or noise in the ear, your doctor may refer you to the following examinations:
- Audiometry (hearing test). Hearing examination is performed by an otolaryngologist specialist. With the help of a special electro-acoustic device, the doctor tests the hearing acuity, the hearing threshold and the sensitivity to various sounds. This is a painless examination, during which the patient is put on a headset, which gives different sound signals. The volume and height of the sound during the examination are changed. When the patient hears the sound, he presses the button to confirm that they have heard the sound. The result of a hearing test or audiometry is plotted on a graph (audiogram) showing the degree and nature of the hearing impairment. In the case of vestibular schwannomas, these hearing disorders are sensory neural hearing loss.
- Image diagnostics. Magnetic resonance imaging (MR, MRI) for the brain with contrast is the gold standard of examination for the diagnosis of even very small (1-2mm) auditory nerve tumors. If MRI is not available or for various reasons a patient can’t do one, the doctor may prescribe computed tomography (CT, CT) examinations for head. It should be remembered that small size nerve VIII tumors may not be seen in a CT scan.
What are the treatment options for vestibulocohleral schwannoma?
The tactics used to treat auditory nerve Schwannoma may vary depending on size, growth, symptoms, and general health. Your doctor may advise you on one of the possible tactics – observation, surgery or radiation therapy. These tactics may change over time.
- Observation. If the tumor is very small, diagnosed accidentally and has little or no symptoms, or the patient is of great age or at risk of any more aggressive treatment, the doctor may recommend the tumor to be monitored. Observing means regular every 6- 12 months magnetic resonance imaging and hearing test (audiogram) examination. If the examinations show evidence of tumor growth, or if it causes the symptoms to progress, your doctor may recommend surgery or radiation, depending on the situation.
- Operation. The goal of the surgical treatment is to maximaly remove the tumor and anatomically and functionally preserve the facial nerve.
The facial nerve (Lat. N. Facialis, Cranial nerve VII) is localized closely to the vestibulocochlear nerve (Cranial nerve VIII). They move side by side from the brain stem and enter the inner ear passage together, so the risk of damage to the facial nerve is one of the first complications of surgery that you will be told by your doctor before surgery.
Nowadays, the probability of facial nerve damage is greatly reduced by monitoring the function of the facial nerve during surgery. About 72% of patients can fully maintain facial nerve function.
The operation is performed under general anesthesia through a small bone window in the skull. If the tumor or part of the tumor is located in the inner ear canal (intracanalicular schwannoma), it may be necessary to open the inner ear canal in addition to maximal tumor removal.
In some cases where there is a high risk of damage to the facial nerve or when the tumor grows tight at the base of the brain or reaches the inner ear structures, the surgeon may decide not to completely remove the tumor during surgery.
The risk of facial nerve damage is much higher for large (> 3 cm) and / or Schwannomas localized to the inner ear aisle.
Risks / possible complications of surgery:
- Damage to the facial nerve; unilateral weakness or paralysis of facial muscles.
- Hearing loss if hearing has been retained before.
- Flow of cerebrospinal fluid through the operation wound or nose.
- Tinnitus or noise in ears.
- Infection; meningitis.
- Stroke or bleeding in the operating room or surrounding brain structures.
- The recurrence Schwannoma or relaps.
- Radiotherapy. There are several types of radiation therapy for vestibular schwannoma.
Stereotactic radiation surgery (stereotactic radiosurgery). Your doctor may recommend such treatment if the tumor is small in size (less than 3 cm), has tumors in both vestibulocochlear nerves (patients with bilateral schwannomas, such as neurofibromatosis type 2), after a previous surgery for the remainder of the high-risk tumor; the patient is elderly or due to other reasons surgery is not possible.
This treatment is carried out with special radiation therapy device and substantially, despite the name, it is a tumor-targeted and highly accurate radiation of a certain radioactive radiation dose. Prior to treatment, the physician, using special computer programs, creates a radiation plan based on the exams performed, depending on the size and location of the particular tumor, in order to minimize any damage to subtle structures surrounding it. During radiosurgery, the radiation of the tumor occurs at a high single dose of radiation.
Depending on the device, the patient’s head is fixed in a special mask or frame. This is done to prevent minor head movements and maintain maximum accuracy. The purpose of radiation therapy, like surgery, is to stop the growth of schwannoma, to maintain the function of the facial nerve and, possibly, hearing. It may take months and even years for the magnetic resonance imaging to observe the effect of radiation therapy as schwannoma reduction in the size.
Stereotactic radiation therapy. Like stereotactic radiosurgery, or radiation surgery, it is an accurate radiation therapy method in which the dose of radiation is divided into several irradiation sessions rather than a single dose.
Irradiation (both stereotactic radiosurgery and stereotactic radiation therapy), like surgery, has risks and those are similar – hearing loss, weakness of facial muscles due to damage to the facial nerve (about 6% risk), tinnitus, imbalance and inefficiency.