Acoustic neuroma- symptoms, diagnosis, and treatment

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Acoustic neuromas

Disease Disorder name: Benign neoplasm of cranial nerves

ICD-10	C72.4	Acoustic neuritis: Degeneration of acoustic or eighth nerve NOS Disorder of acoustic or eighth nerve
ICD-9	225.1	Acoustic neuritis: Degeneration of acoustic or eighth nerve NOS Disorder of acoustic or eighth nerve

Introduction

Incidences of acoustic neuromas in the United States are quite rare. Only about 3000 cases are diagnosed each year in the United States or an incidence rate of about 1 in 100,000.

Description

An acoustic neuroma is a benign, slow-growing neuroma (Can grow over years) that originates in the canal (nerve pathway) connecting the brain to the inner ear. It is along this pathway (8th cranial nerve) that the electrical and chemical signals for heard sounds are transmitted from the inner ear to the brain. Other names for this type of neuroma include ‘vestibular schwannoma’ and ‘neurinoma’.

Pathology

These neuromas tend to cause gradually increasing deafness rather than any balance problems. Once large, they compress the brain stem, the stalk that the brain sits on.

Symptoms

Common symptoms include:

Tinnitus
Hearing loss
Vertigo
Continual headaches with any movement of the head
Dizziness
Loss of balance
Numbness or pain in the face on the side of the affected ear

Symptoms of advanced acoustic neuroma:

Facial drooping on one side
Unsteady walk
Drooling
Nausea and vomiting
Dilated pupil on affected side
Sleepiness

Diagnosis

Acoustic neuroma can be diagnosed using a variety of tests, including:

Computed tomography (CT) scan – a specialized x-ray that takes three-dimensional pictures of the inner ear. However, small neuromas may be missed by this method.
Magnetic resonance imaging (MRI) scan – pictures of the inner ear are taken, using radio waves in a strong magnetic field instead of x-rays. MRI scans can usually detect smaller acoustic neuromas than CT scans. A dye may be injected to further highlight the tissues under investigation.

Treatment for acoustic neuromas

The only treatment for an acoustic neuroma, assuming it has grown to where it is seriously effecting the daily activities of a person, is either surgical removal, or bombarding the neuroma with radio waves to destroy the tissue (radiation therapy).

Physical Surgery
- Surgical methodology will depend on the size of the neuroma.
  - If a neuroma is removed when it is very small, hearing may be preserved, but not guaranteed. Any hearing that is lost prior to surgery will not be regained.
  - Large neuromas that have grown to also compress the nerves for facial movement and sensation can typically be safely removed, but the surgery often results in paralysis of some facial muscles and total loss of hearing on that side.
  - Extremely large neuromas may also compress the brainstem, threatening other cranial nerves and preventing the normal flow of cerebrospinal fluid. This can lead to a build-up of fluid in the head (hydrocephalus) which can cause a potentially life-threatening situation. Surgery in these cases is performed in two phases. The first surgery is to immediately treat the hydrocephalus and decompress of the brainstem by draining excess fluid and keeping a stent into the brain cavity to keep the cavity free of fluid buildup. A second surgery will then remove the neuroma. Sometimes both operations are performed at the same time (one after the other under the same general anesthesia), however because of the length of time required for the neuroma removal surgery (3+ hours), the surgeries are often split into two sessions.
- Surgery to remove an acoustic neuroma can take from two and one-half hours to over 12 hours. The mastoid bone behind the ear is exposed and partially drilled out. This approach involves drilling through the mastoid bone behind the ear, and removing the semicircular canals.
- Stereotactic radiosurgery: Because physical surgery is extremely traumatic to a patient, the patient must be healthy prior to such an operation. In cases of a sick patient or those who are elderly, radiosurgery is the preferred method. In some cases,
  - Sometimes during brain surgery to treat acoustic neuromas, not all of the neuroma can be safely removed, and some residual neuroma must be left behind. Radiosurgery is also used post-operatively to treat residual neuroma in these cases.
  - Radiosurgery is only appropriate for small neuromas, so that radiation damage to surrounding tissues can be minimized.
  - Like brain surgery, radiosurgery can sometimes result in facial paralysis or loss of hearing.

Expectations (prognosis)

Acoustic neuromas are benign and non-cancerous; they do not spread (metastasize) to other body systems, but they may continue to grow and compress vital structures within the skull.

Surgery results in complete removal of the neuroma in greater than 95% of cases.
About 95% of patients with small neuromas will have no permanent facial paralysis following surgery. However, roughly two-thirds of patients with large neuromas will have some permanent facial weakness following surgery.
Approximately one half of patients with small neuromas will retain useful hearing in the affected ear following surgery.
There may be delayed radiation effects following radiosurgery, including nerve damage, loss of hearing, and facial paralysis.

Consequences of delayed treatment of an acoustic neuroma

Even though acoustic neuromas are benign, they can still be fatal if left untreated. This is because the neuroma will keep growing. Once it runs out of space inside the small canal that links the inner ear to the brain, it begins to grow into the skull cavity. The tissue at the base of the brain, including a structure called the brain stem, may become squashed by the growing neuroma. This can cause a build-up of fluid know as cerebral spinal fluid. The brain stem is responsible for regulating important bodily functions, including consciousness, heart rate, breathing, blood pressure and swallowing.