Acoustic Neuroma

What is an Acoustic Neuroma?

An Acoustic Neuroma, also known as Vestibular schwannoma, is a noncancerous tumor inside the skull, arising from the covering of a nerve called the vestibulocochlear nerve. The vestibulocochlear nerve (also known as the acoustic nerve) is one of the nerves that arise directly from the brain, and it connects to the inner ear and plays a vital role in hearing and balance. It is a slow-growing tumor and is usually seen in the 30 to 60 years age group, and affects men and women equally.

Is Acoustic Neuroma a Medical emergency?

An Acoustic Neuroma is not a medical emergency.

Causes

An Acoustic Neuroma develops from the Schwann cells on the vestibular portion of the vestibulocochlear nerve, which is the 8^th cranial nerve. The Schwann cells make the myelin sheath, which is the protective covering of the nerves. The exact cause of the Schwann cell overgrowth and tumor formation is not known but it may be related to certain faulty genes on the 22^nd chromosome whose normal function is to suppress the growth of tumors.

Risk factors

There are no noticeable risk factors for an Acoustic Neuroma and it can develop spontaneously in anybody. Individuals with neurofibromatosis type II (NF2) also have a faulty tumor suppression gene on their 22^nd chromosome and tend to develop Acoustic Neuromas in addition to other nerve tumors common to the condition.

Symptoms & signs

The symptoms and signs of an Acoustic Neuroma may include the following:

• Hearing loss on one side - Which develops gradually
• The gradual loss of speech comprehension
• Tinnitus - Ringing in the ears
• Loss of balance and unsteadiness
• Dizziness or vertigo
• The feeling of fullness or pressure in the ear
• Numbness or tingling of the face
• The weakness of the facial muscles

The symptoms and signs of large and very large tumors may include:

• Headaches
• Altered gait
• Vomiting
• Confusion

Investigations

The following investigations may be done:

• Routine laboratory tests: These are usually not required, but may be done if the general health condition of the individual requires them, especially before surgical intervention.
• Imaging tests:
  • MRI: A gadolinium-enhanced MRI is the preferred imaging test, as it is able to identify very small tumors as well
  • CT scan: If MRI is unavailable or cannot be tolerated, a normal CT scan may not detect small-sized tumors
  • Air contrast cisternography: If MRI can’t be done, but there is a suspicion of small tumors that cannot be detected by a normal CT
• Acoustic (hearing) tests:
  • Pure tone audiometry: Preferred over routine audiometry
  • Auditory brainstem response test: Detects the passage of electrical impulses from the inner ear to the brain. It cannot identify tumors that are small or in individuals with good hearing.

Diagnosis

A diagnosis of Acoustic Neuroma is established based on medical history, clinical evaluation, and the results of the investigations done.

Treatment options

The treatment of an Acoustic Neuroma depends on the size and the severity of the symptoms. It may be managed by watchful waiting, surgical intervention, or radiation.

Interventional including surgery and indications for surgery

Surgical intervention is one of the approaches to the management of an Acoustic Neuroma, and the aim of surgery is to remove the tumor, preserve the function of the other cranial nerves, and preserve hearing.

The general indications for surgery include:

• A large tumor which cannot be managed by radiation
• Rapidly growing tumor
• Cystic (fluid-filled) tumor
• Preservation of hearing especially in young individuals

Surgical intervention involves removal of all or a major portion of the tumor and the procedures involved are:

• Retrosigmoid approach: It is a surgery done by approaching the tumor through the occipital bone which is at the back and bottom portion of the skull. Even very large tumors can be removed through this approach.
• Translabyrinthine approach: It is a surgery done by approaching the tumor by entering the skull from behind the ear and then through the internal auditory canal. Hearing cannot be preserved in this approach.
• Middle cranial fossa approach: It is a surgery done by approaching the tumor from in front of the ear and through the temporal bone which is present on the side and the middle of the skull, it is suitable even for small tumors.

Other surgeries or interventions that may be needed include:

• Cochlear implants to health with hearing loss

Radiation

Radiation therapy may be an option for the management of an Acoustic Neuroma and the aim of radiotherapy is to stop tumor growth, preserve the function of the other nerves, and preserve hearing.

It may be done in the following circumstances:

• The size of the tumor is small and hearing is good
• Elderly individuals
• Surgery is contraindicated due to the presence of other health conditions.
• Individuals refuse surgical intervention

The advantages of radiation therapy include:

• Shorter hospital stay
• Lesser post-treatment complications
• Hearing is retained, at least in the short term

Radiation therapy may be done as:

• Stereotactic radiosurgery: It is done using precisely targeted application of beams of radiation onto the tumors without affecting the surrounding tissues. It is done as a single high dose of treatment.
• Stereotactic radiotherapy: It is done over multiple sessions and delivers hypofractionated radiation by precisely targeting the tumor and sparing the surrounding tissue.

Role of diet/ Exercise/ Lifestyle changes/ Preventive measures

Simple observation or watchful waiting is sometimes the only management that is done in some individuals without resorting to surgical interventions or radiotherapy.

Monitoring is done under the following circumstances:

• The size of the tumor is small and the hearing is good, especially in young individuals.
• Elderly individuals.
• Intervention and radiotherapy are contraindicated due to the presence of other health conditions.
• Individuals refuse surgical intervention.

Other supportive therapy may be required after surgical interventions or radiotherapy and may include:

• Physical therapy: To help with balance and posture

Complications

The following complications are associated with an Acoustic Neuroma or its management:

Complications of an untreated Acoustic Neuroma:

• Hearing loss
• Ringing in the ears
• Facial paralysis and weakness
• Loss of gag and swallowing reflexes
• Raised intracranial tension (pressure inside the skull)
• Loss of balance and coordination

The complications of surgical intervention may include:

• Hearing loss
• Bleeding
• Infection of the wound
• Facial muscle paralysis or weakness
• Injury to the arteries supplying the brain
• Injuries to the brain and cerebellum
• Leakage of cerebrospinal fluid
• Postoperative bacterial meningitis (due to infection of the cerebrospinal fluid)
• Stroke
• Persistent headache
• Problems with balance and coordination

Complications of radiotherapy:

• Failure to control tumor growth
• Long term balance and coordination problems
• Injury to neighboring cranial nerves
• Possibility of secondary cancers

Prognosis

The prognosis of Acoustic Neuroma is generally good, and it depends on factors such as the size, rate of growth, age, and general health condition of the individual. Quality of life may be affected due to hearing loss and problems with balance.

When to contact the doctor or hospital? / How to identify the emergency or complications?

It is advisable to seek medical attention if the symptoms of an Acoustic Neuroma are noticed.

Indications for hospitalization if required

Hospitalization will be required for the surgical management of an Acoustic Neuroma.

Suggested clinical specialist/ Departments to consult for this condition

• Neuro-oncologist
• Neurologist