Acoustic Neuroma: Types, Symptoms, Causes, Treatments, Surgery, MRI

Overview

A person may experience one-sided hearing loss, ringing in the ears, and loss of balance. These symptoms can indicate numerous health conditions. One of them is an acoustic neuroma. 

Acoustic neuroma is a non-cancerous tumour affecting the nerve tissues that run from the inner ear to the brain. The nerve is responsible for hearing and balance. But when the tumour presses on the nerve, it causes hearing loss and ringing in the ears, known as tinnitus. As the tumour progresses, it increases the pressure on the brain, which could be fatal. However, it is essential to note that the tumour does not spread to other body parts. 

The blog delves deep into the acoustic neuroma, its symptoms, causes, and various treatments. 

What is acoustic neuroma?

Acoustic neuroma or vestibular schwannoma is a benign and slow-growing tumour that grows in the vestibular nerve that runs between the inner ear and the brain. The various branches of the vestibular nerve are responsible for balance and hearing. However, when the tumour increases the pressure on the nerve, it results in hearing loss, ringing in the ears, and loss of balance. 

Typically, acoustic neuroma affects the Schwann cells that cover and support the nerves. In rare cases, the tumour rapidly grows and enlarges, causing increased pressure on the brain and may interfere with the body’s vital functions. It could be fatal. But, as mentioned earlier, the tumour does not spread to other body parts. Patients with acoustic neuroma require regular monitoring, radiation, and, sometimes, surgery to prevent the symptoms from worsening.

The National Orgnization of Rare Diseases (NORD) study shows that acoustic neuroma affects one in every 1,000 people, and nearly 2500 new cases are registered in the United States annually. People between the age of 30 to 60 are susceptible to developing acoustic neuroma. 

Acoustic neuroma has several other names, such as acoustic neurinoma, vestibular schwannoma, and auditory nerve tumour.

What are the types of acoustic neuroma?

There are two different types of acoustic neuroma. They are as follows:

• Sporadic, unilateral acoustic neuroma: In nearly 95% of the patients, the tumour grows on one side of the body. These tumours are sudden and non-hereditary mutations. Sporadic, unilateral acoustic neuroma can occur at any age but is commonly seen in patients between the age of 30 to 60.
• Genetic, bilateral acoustic neuroma: As the name suggests, the tumour occurs on both sides of the body. People with neurofibromatosis type 2, a genetic disorder, are susceptible to this acoustic neuroma. In neurofibromatosis, the mutation of chromosome 22 affects Schwann cell production resulting in schwannoma-like tumours in the entire body. Treatment for this is different from that of unilateral tumours.

What are the symptoms of acoustic neuroma?

Hearing loss, dizziness, ringing in the ears, are  common ear symptoms in many other ear disorders . Therefore, diagnosing acoustic neuroma can be challenging, and doctors can easily miss it as it may take years to develop. As the tumour affects the nerves responsible for balance and hearing, the following are some of the symptoms of acoustic neuroma:

• One-sided hearing loss: More than 90% of acoustic neuroma patients develop a certain degree of one-sided hearing loss. Such patients have difficulty listening and locating noises in a crowded place and find it challenging to follow or hold a conversation for a long time. The hearing loss typically worsens over the years and may result in complete deafness in one ear. The sudden loss of hearing is one of the first signs that can lead to diagnosis or may occur before the tumour is discovered – for months or years. When there is a compression on the nerve that is responsible for hearing, it  affects  the way a patient hears sounds and the clarity of hearing. Mild hearing loss may not be noticeable and can lead to delayed diagnosis.

• A feeling of fullness in ears: Patients with acoustic neuroma often experience a sense of fullness in their ears, similar to if their ears are filled with water. It is due to hearing loss due to the tumour.
• Ringing in the ear: The ringing in the ear is known as tinnitus. It is a common symptom of several ear-related disorders and acoustic neuroma. Some patients experience a high-pitched tone in the affected ear, whereas others experience sounds similar to hissing, buzzing, or roaring. Patients may experience tinnitus and hearing loss or may only experience only tinnitus. The ringing in the ear recurs or is constant, with single or multiple tones. Sometimes, the noise can be quiet or high.
• Loss of balance and vertigo: These are early signs of acoustic neuroma. As the tumour grows, it compresses the cerebellum resulting in falls and worsening symptoms. When patients lose their balance and fall, they fall on the side of the tumour. The sense of spinning or tilting, known as vertigo, is not typically linked to acoustic neuroma but can occur due to the growing tumour or bleeding.

Since the tumour puts immense pressure on other cranial nerves that are closer to the tumour, it causes other following symptoms:

• Face numbness: When the tumour presses on the trigeminal nerve, it may result in ongoing or periodic facial numbness and tingling on the affected side. Other symptoms may include tingling near the corner of the mouth or cheek, eye irritation, eye redness, and numbness in the eyes that affects the  blinking reflexes.
• Facial twitching and weakness: Tumour that presses on the facial nerves may cause facial twitching and weakness. Facial numbness also occurs during the later stages of acoustic neuroma and is the lesser-known symptom during diagnosis.
• Difficulty swallowing: A patient may find swallowing difficult when the tumour presses on the vagal and hypoglossal nerves that control swallowing, including the sensation in the throat and movement of vocal cords and tongue. 
• Taste and tear production changes: It is a lesser-known symptom that requires medical attention. The pressure on the nerve that controls taste and tear production results in dry eyes or unexpected tears and changes in taste. 
• Immense headaches and pressure: As the tumour grows, it puts pressure on the lining of the inside of the skull, called the dura. There are several sensory fibres present in the dura. Headaches from acoustic neuroma may be dull or aching and are typically on one side of the head. The patient may experience pain radiating to the neck, top, or front of the head.

Cholesteatoma, labyrinthitis, vestibular neuritis, and Meniere’s disease also cause the above mentioned symptoms. Occasionally, an acoustic neuroma becomes large that it can compress the brainstem and become fatal. 

When to seek medical help?

If a person notices the symptoms of acoustic neuromas, such as hearing loss on one side, ringing in the ear, or loss of balance, seeking medical help is required. Early diagnosis may prevent the tumour and symptoms from developing further.

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What are the causes of acoustic neuroma?

There are two forms of acoustic neuroma: sporadic and genetic acoustic neuroma, and the cause of genetic neuroma is due to abnormalities in chromosome 22. The mutated gene is inherited from parents. However, experts do not know the reason for sporadic acoustic neuroma. Close to 95% of acoustic neuromas occur without any particular cause.

Who is at risk of developing acoustic neuroma?

Anyone can develop an acoustic neuroma. However, some populations, such as Asian Americans and black Americans, are at a higher risk of developing acoustic neuroma. Also, as people reach the age of 65 to 74, it makes them more susceptible to developing the disease. Men and women have equal chances of developing acoustic neuroma.

How is acoustic neuroma diagnosed?

After conducting a complete physical examination and noting down the various symptoms, the doctor recommends hearing and balance tests and scans, such as the following: 

• An audiogram helps the doctor check the patient’s hearing ability
• Electronystagmography checks for balance and records eye movements and helps the doctor detect any abnormalities in the nerve functioning of the eyes and the ears
• Auditory brainstem response measures the hearing nerves’ response to sounds and checks for the brainstem’s proper functioning.
• MRI and CT scans allow the doctor to locate the tumour and measure the tumour size

What are the treatment options for acoustic neuroma?

Based on the severity of the symptoms and the tumour size, the doctor decides on either of the three potential treatment options – monitoring, surgery, or radiation therapy.

• Monitoring: For a tumour that is small in size or is gradually growing with no or few minor symptoms, the doctor may recommend constant monitoring of the tumour. It is usually recommended for older adults who are not the right candidate for aggressive treatments. Yearly or bi-year imaging and hearing tests help determine the growth of the tumour and how quickly it is progressing. However, if the test results indicate a progressive development in the tumour causing significant difficulties, the patient needs to undergo treatment.

• Surgery: If the tumour continues to grow, is large in size, and causes severe symptoms, the healthcare provider may recommend several surgery  to remove the acoustic neuroma. The surgery aims to remove the tumour and prevent facial paralysis. In some instances, the entire tumour may not be removed entirely as it may be in close proximity to the brain or facial nerves. The outcome depends on the size of the tumour, hearing status, and other factors. Suboccipital, translabyrinthine, and middle fossa craniotomy are three standard surgical procedures performed by surgeons. 

• Suboccipital or retrosigmoid craniotomy: This procedure is typically recommended for patients with a large tumour. In this surgery, the doctor accesses the tumour from behind the head as it gives a better view of the nerves responsible for swallowing. The surgery may help preserve hearing and inner ear structure. 
• Translabyrinthine craniotomy: The procedure is recommended by doctors for patients with complete loss of hearing. In this procedure, the surgeon removes a small bone behind the ear to gain access to the tumour through the inner ear. It provides a clear view of the entire facial nerve and requires minimum brain retraction. 
• Middle fossa craniotomy is typically performed on patients with smaller acoustic neuromas and almost intact hearing. Doctors consider this procedure to give patients an excellent chance at preserving their hearing. However, like most surgeries, even this has a risk of developing weakness in the facial nerve. The procedure is not recommended for patients with a medium to a large tumour. 
• Radiation therapy: The following are some radiation therapy doctors recommend to treat acoustic neuroma:

• Stereotactic radiosurgery: The doctor recommends this form of radiation therapy for small tumours less than 2.5 centimetres in diameter and for individuals aged or unable to tolerate surgery due to several health conditions. In this procedure, the doctor doesn’t make an incision but uses numerous tiny gamma rays to send a targeted radiation dose to a tumour without harming the surrounding tissues. This radiosurgery aims to prevent a tumour’s growth and protects the facial nerves and hearing function
• Proton beam therapy: Here, the doctor uses high-energy beams of positively charged particles called protons. It is delivered to the affected areas in a targeted dose to eliminate tumours and minimizes radiation exposure to the surrounding area.
• Supportive therapy: Apart from treatment to remove or prevent the growth of the tumour, the doctor may also use several supportive therapies to treat symptoms, including dizziness and balance issues. Doctors may recommend a cochlear implant to treat hearing loss. 

What are the risk factors for an acoustic neuroma?

The only risk factor known for acoustic neuroma is neurofibromatosis 2 – a genetic condition that is passed on from one of the parents. Most of these tumours spontaneously arise in people with no family history of the disease.

What are the complications of acoustic neuroma?

After treatment, certain patients experience the following complications:

• Facial nerve damage: It is not permanent. The patient should be able to recover in a few months or a year. However, if the doctor believes the facial nerve damage to be permanent, a surgeon performs nerve transfer surgery or other procedures to restore facial movements.
• CSF leaks: CSF leaks if there is a leak or a hole in the membrane that covers the brain and spinal cord, called the dura. It can be treated by blocking the hole through a procedure.
• Constant hearing loss: In such situations, the doctor may prescribe a bone-anchored hearing aid, cochlear implant, or a regular hearing aid
• Neurofibromatosis type 2 patients with acoustic neuroma in both ears may have deafness. In such cases, the doctor recommends cochlear implants or auditory brainstem implants that provide a sense of sound and gives the patient a chance to understand speech

Conclusion

Acoustic neuroma has various treatment options to prevent worsening symptoms. The patient can lead a normal, daily life with timely medical intervention. 

Frequently Asked Questions (FAQs)

What are the possible complications from surgery?

The following are the complication of acoustic neuroma:

• CSF leaks through the wound or the nose
• Loss of hearing
• Weakness or numbness in the face
• Ringing in the ear
• Issues in balance
• Persistent headache
• In rare cases, infection of the cerebrospinal fluid
• In severe cases, a stroke or brain bleed

Is acoustic neuroma preventable?

Unfortunately, acoustic neuroma is not preventable. With timely intervention, the patient can easily prevent the symptoms from worsening.

Can an acoustic neuroma be cancerous?

An acoustic neuroma is a benign tumour (not cancer). These non-cancerous tumours do not spread to other body parts like cancerous tumours. These tumours lead to problems by growing and pressing on the essential structures and nerves. These tumours also tend to grow slowly, sometimes over many years.

How is an acoustic neuroma diagnosed?

The doctor consults people about the symptoms and performs a physical exam. They may also undergo hearing and balance tests and scans, including audiograms, electronystagmography, auditory brainstem responses, MRIs, and CT scans.