Is an acoustic neuroma benign or malignant? Will it affect hearing?

Author: Jia Wang, Chief Physician, Beijing Tiantan Hospital, Capital Medical University

Reviewer: Xing Yan, Chief Physician of Aviation General Hospital

Acoustic neuroma is a very common tumor in the brain, accounting for about 7%-9% of all brain tumors. There is 1 new case of acoustic neuroma per 100,000 people each year.

1. What kind of tumor is acoustic neuroma?

The auditory nerve is the eighth cranial nerve. If we compare the arm to a nerve, the surface of each nerve is covered with a nerve sheath, just like clothes. When this sheath becomes thicker and thicker, from a single piece of clothing to a down jacket, a tumor is formed, called a neurothecoma, which is not a tumor originating from the nerve itself.

Figure 1 Original copyright image, no permission to reprint

Fortunately, all acoustic neuromas are benign and will not turn into cancer. As long as the correct treatment is adopted, the cure rate can reach over 95%. It is a tumor with very good treatment effects.

The cause of acoustic neuroma is not very clear at present, so there is no good way to prevent it.

2. What are the symptoms of acoustic neuroma?

Acoustic neuroma is a very hidden tumor.

The earliest clue is a decrease in speech recognition rate. For example, someone speaks to you and the sound passes by your ear, but you don’t understand what is said. It may feel like a lack of concentration or a decline in attention. This stage may pass quickly and enter the tinnitus stage.

Acoustic neuroma originates from the vestibular nerve. In such a small space, the vestibular nerve will constantly stimulate the cochlear nerve. During the stimulation process, a rumbling noise may begin to appear. This noise may not be heard in a noisy environment.

When the tumor grows larger, the nerves are under continuous compression, and persistent high-pitched tinnitus will occur, like the chirping of cicadas in summer, day and night.

The third is hearing loss. If one side has an acoustic neuroma, the hearing on that side will be reduced. You will feel that you cannot hear things clearly on that side and cannot figure out the source of the sound. Suddenly, you will find that you always use this ear to answer the phone. Even if the phone is in your right pocket, when you take it out, you will switch it to your left hand to answer it. Subconsciously, you will think that the good, healthy ear can hear more clearly.

Of course, some people may feel like they are stepping on sponges when walking, and feel that the ground is not solid. Another reason is that they walk crookedly, which is because the acoustic neuroma has damaged the vestibular function.

Another very common symptom of acoustic neuroma is sudden deafness. Many patients go to the otolaryngology department because of sudden deafness, and acoustic neuroma is discovered through magnetic resonance imaging.

When the acoustic neuroma grows larger and enters the middle stage, it will begin to affect the upper and lower nerves. The upper one is the trigeminal nerve. First, numbness will appear in the trigeminal nerve distribution area. The face will be very numb and numb, and you can't feel it even when you touch it with your hands. If it presses downward, it will compress the glossopharyngeal nerve, and it will be easy to choke when drinking water or porridge. This is an ultimate symptom.

When an acoustic neuroma grows particularly large, it will compress the brain stem, causing limb movement disorders, leading to hydrocephalus and severe headaches. The increased intracranial pressure caused by hydrocephalus may also cause blindness, and in more serious cases, even death.

Therefore, once an acoustic neuroma is diagnosed, it must be treated promptly.

The gold standard for diagnosing acoustic neuromas is enhanced MRI, which can detect very small acoustic neuromas at an early stage. In addition, MRI can determine the size of the tumor, as well as the extent of the tumor's blood supply, the degree of adhesion to other nerves, and the degree of compression on the brainstem, providing us with a lot of information.

Figure 2 Original copyright image, no permission to reprint

3. How to treat acoustic neuroma?

There are currently two treatments for acoustic neuromas in the world: surgery and gamma knife. After an acoustic neuroma is discovered, surgery may not be necessary immediately, but all acoustic neuromas will eventually require surgery.

If the acoustic neuroma is very small and there is no hearing loss, but only tinnitus or paroxysmal vertigo symptoms, you can observe for half a year. If the symptoms do not change and the size of the tumor does not change after half a year, you can observe for another half a year. If the tumor is growing, the tinnitus feels more severe than before, and the vertigo is more frequent than before, surgical treatment is required.

In addition, during the observation process, you may face the risk of sudden deafness. Once the tumor affects the blood supply to the auditory nerve, sudden deafness may occur. Once sudden deafness occurs, hearing cannot be restored even if surgical resection is performed.

The preferred treatment for acoustic neuroma is surgical resection. Otolaryngologists generally use an incision behind the ear, provided that hearing has been lost. This is suitable for treating small acoustic neuromas in patients with hearing loss. The advantage is that the incision is smaller and the exposure is very narrow. This surgical method is not used for patients with larger tumors or those who still have hearing. Neurosurgeons use craniotomy, which can treat acoustic neuromas of any size, preserve the facial nerve function, and preserve hearing.

Gamma Knife is an auxiliary technology invented in recent years. It is suitable for very special groups of people, such as very elderly patients with acoustic neuroma. The risk of surgery is greatly increased. Through the auxiliary treatment of Gamma Knife, they can live with the tumor. For patients with acoustic neuroma who have very high requirements for facial appearance, although the surgery is now very minimally invasive, it cannot be 100% guaranteed that there will be no change on the face after the surgery. If the tumor is relatively small, Gamma Knife treatment can be used. For patients with acoustic neuroma who are particularly afraid of surgery, it is not wise to choose Gamma Knife because it cannot achieve 100% control. For patients who have undergone surgery once and the acoustic neuroma was not completely removed, there is a small amount of remnant, and Gamma Knife can be considered for auxiliary treatment.