Acoustic Neuroma

acoustic neuroma
An acoustic neuroma, also called a vestibular schwannoma, is a non-cancerous tumor that occurs around your balance and hearing nerves that connect your inner ear with your brain.
The term schwannoma means the tumor developed from Schwann cells. These cells surround nerves in the peripheral nervous system (nerves outside the brain and spinal cord) and normally insulate and support the function of nerves. Schwannomas can occur in nerves across the body, but in the head, these most commonly occur from the vestibular nerve, or balance nerve.

Types of Acoustic Neuroma

There exist two distinct categories of acoustic neuromas:

  1. Unilateral acoustic neuromas: These exclusively impact one ear and represent the most prevalent form of acoustic neuroma. This type of tumor can develop at any stage of life, although it predominantly occurs between the ages of 30 and 60. The emergence of acoustic neuromas in some cases can be attributed to nerve damage induced by environmental factors. The sole established environmental risk factor is previous exposure to radiation directed at the head. The role of prolonged exposure to loud noises in the development of acoustic neuromas remains unclear.

  2. Bilateral acoustic neuromas: This variant affects both ears and is hereditary in nature. It arises due to a genetic anomaly known as neurofibromatosis-2 (NF2).

Symptoms of Acoustic Neuroma

The most common symptom is hearing loss in one ear (unilateral). This symptom happens to about 90% of people who have an acoustic neuroma.

Other symptoms that may occur in the early stages include:

  • Ringing in the ears (tinnitus).
  • Loss of balance.
  • Sensation that you or your environment is moving (vertigo).

As the tumor grows, you may have other symptoms, including:

  • Blurry or double vision.
  • Facial numbness, weakness, spasms, pain, or paralysis.
  • Taste changes.
  • Headaches.
  • Nausea and vomiting.
  • Swallowing difficulty.

Symptoms of acoustic neuromas can mimic symptoms of other ear problems. This similarity makes it challenging to diagnose an acoustic neuroma. Talk to your healthcare provider if you notice any hearing changes.

Causes of Acoustic Neuroma

In most cases of acoustic neuromas, the underlying cellular cause can be attributed to the failure of a regulatory gene, often referred to as a “governor” gene, to effectively inhibit the proliferation of Schwann cells. Schwann cells play a crucial role in insulating nerve fibers. When this inhibition mechanism falters, these cells begin to overmultiply, ultimately giving rise to the formation of acoustic neuromas.

As for environmental factors, the only firmly established link to an increased risk of developing acoustic neuromas is exposure to radiation targeting the head. There is currently no compelling evidence to suggest any association between the use of cell phones and the onset of these tumors.

It’s worth noting that acoustic neuroma is typically not considered a hereditary condition. However, approximately five percent of cases are connected to a genetic disorder known as neurofibromatosis type 2 (NF2). In individuals with NF2, bilateral vestibular tumors are common, often accompanied by the presence of other tumors within the brain and/or spinal cord. The majority of acoustic neuromas, though, occur sporadically and are not tied to hereditary factors.

Diagnostics of Acoustic Neuroma

Your healthcare provider will ask you about your symptoms and perform a physical exam. You will also have a series of hearing and balance tests and scans, which may include:

  • Audiogram to check hearing ability.
  • Electronystagmography, which tests balance and records eye movement to check how your eye and ear nerves are functioning.
  • Auditory brainstem response to measures how hearing nerves response to sound and check brainstem function.
  • MRI and CT scans to locate the tumor and measure its size.

Complications of Acoustic Neuroma

An acoustic neuroma can lead to lasting complications, such as:

  1. Impaired hearing
  2. Facial numbness and muscle weakness.
  3. Issues with balance.
  4. Persistent tinnitus (ringing in the ear).

In cases where the tumors grow to a significant size, they may exert pressure on the brainstem, potentially obstructing the normal flow of cerebrospinal fluid between the brain and spinal cord. This obstruction can result in the accumulation of fluid within the cranial cavity, a condition referred to as hydrocephalus. This elevated fluid buildup inside the skull subsequently raises intracranial pressure.

Treatment of Acoustic Neuroma

Your healthcare provider will discuss your treatment options with you. Your treatment plan will depend on:

  • Tumor size and location.
  • Your age and overall health.
  • Degree of damage to your hearing and balance nerves.

Treatment options include:

  • Observation: If the tumor is small, not growing and not causing any symptoms, your healthcare provider may recommend monitoring the tumor but not actively treating it. You will have regular MRI scans to see if the tumor is growing. If it does grow or cause symptoms, your provider can quickly switch to active treatment.
  • Radiosurgery: For small and medium tumors, this approach may stop tumor growth. You receive a single high dose of targeted radiation therapy, delivered directly to the tumor. This approach limits the amount of radiation that affects surrounding, healthy tissues. You will need ongoing scans during treatment to watch for any tumor growth.
  • Microsurgery: This type of surgery uses instruments designed to operate on small, delicate areas. The goal is to remove as much of the acoustic neuroma as possible while preserving your facial nerve function. Surgery is the only treatment option that permanently removes the tumor. In some cases, surgeons can preserve your hearing, though not always. The smaller the tumor, the more likely it can be removed and hearing preserved.