Acoustic neuroma

Other Names : Acoustic neurilemmoma, Acoustic neurinoma, Auditory tumor, Vestibular schwannoma


Definition:

Acoustic neuroma is a non-cancerous tumor that develops on the nerve that connects the ear to the brain.  The neuroma actually arises from cells called Schwann cells that cover the nerve, rather than from the nerve itself, and is therefore correctly called a vestibular schwannoma.

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The tumor usually grows slowly. As it grows, it presses against the hearing and balance nerves. At first, you may have no symptoms or mild symptoms. They can include

*Loss of hearing on one side
*Ringing in ears
*Dizziness and balance problems

Acoustic neuroma can be difficult to diagnose, because the symptoms are similar to those of middle ear problems. Ear exams, hearing tests and scans can show if you have it.

If the tumor stays small, you may only need to have it checked regularly. If you do need treatment, surgery and radiation are options. If the tumors affect both hearing nerves, it is often because of a genetic disorder called neurofibromatosis. The tumor can also eventually cause numbness or paralysis of the face. If it grows large enough, it can press against the brain, becoming life-threatening.


Symptoms
:
Invariably the acoustic neuroma develops only on one side of the head, causing symptoms to occur in that ear. These may include:

*Ringing (tinnitus) in the affected ear
*Vertigo
*Headaches, facial numbness, deterioration of sight and loss of co-ordination are late symptoms
*Hearing loss, usually gradual — although in some cases sudden — and occurring on only one side or more pronounced on one side
*Unsteadiness, loss of balance
*Dizziness (vertigo)
*Facial numbness and weakness

In rare cases, an acoustic neuroma may grow large enough to compress the brainstem and be life-threatening.

Causes:

The cause of acoustic neuromas — tumors on the main nerve leading from your inner ear to your brain (vestibulocochlear nerve) — appears to be a malfunctioning gene on chromosome 22. Normally, this gene produces a protein that helps control the growth of Schwann cells covering the nerves. What makes this gene malfunction isn’t clear. Scientists do know the faulty gene is inherited in about half the cases of neurofibromatosis 2, a rare disorder that typically involves the growth of tumors on the vestibulocochlear nerve on each side of the head (bilateral neuromas).

Most people are between the ages of 40 and 60 when an acoustic neuroma is discovered but why they develop one in the first place is unclear.

Acoustic neuromas may occur sporadically (meaning the cause is unknown), or in some cases occur as part of von Recklinhausen neurofibromatosis, in which case the neuroma may take on one of two forms.

In Neurofibromatosis type I, a schwannoma may sporadically involve the 8th nerve, usually in adult life, but may involve any other cranial nerve or the spinal root. Bilateral acoustic neuromas are rare in this type.
In Neurofibromatosis type II, bilateral acoustic neuromas are the hallmark and typically present before the age of 21. These tumors tend to involve the entire extent of the nerve and show a strong autosomal dominant inheritance. Incidence is about 5 to 10%.

The usual tumor in the adult presents as a solitary tumor, originating in the nerve. It usually arises from the vestibular portion of the 8th nerve, just within the internal auditory canal. As the tumor grows, it usually extends into the posterior fossa to occupy the angle between the cerebellum and the pons (cerebellopontine angle). Because of its position, it may also compress the 5th, 7th, and less often, the 9th and 10th cranial nerves. Later, it may compress the pons and lateral medulla, causing obstruction of the cerebrospinal fluid and increased intracranial pressure.

Schwannomas can occur in relation to other cranial nerves or spinal nerve roots, resulting in radiculopathy or spinal cord compression. Trigeminal neuromas are the second most common form of schwannomas involving cranial nerves. Schwannomas of other cranial nerves are very rare.

Diagnosis:
Signs and symptoms of acoustic neuroma are likely to develop gradually and because hearing loss, tinnitus and problems with balance can be indicators of other middle and inner ear problems, it may be difficult for your doctor to detect the tumor in its early stages. Acoustic neuromas often are found during screening for other conditions.

After asking questions about your symptoms, your doctor will conduct an ear exam and may request the following tests:

*Hearing test (audiometry). During this test conducted by a hearing specialist (audiologist), you wear earphones and hear sounds directed to one ear at a time. The audiologist presents a range of sounds of various tones and asks you to indicate each time you hear the sound. Each tone is repeated at faint levels to find out when you can barely hear. The audiologist will also present various words to determine your hearing ability.

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*Brainstem auditory evoked response (BAER). This test checks hearing and neurological functions. Electrodes on your scalp and earlobes capture your brain’s responses to clicking noises you hear through earphones and record the responses on a graph.

*Electronystagmography (ENG). This test evaluates balance (vestibular) function by detecting abnormal rhythmic eye movement (nystagmus) often present with inner ear conditions. The test measures your involuntary eye movements while stressing your balance in various ways.

*Scans. Magnetic resonance imaging (MRI) or computerized tomography (CT) scans of your head can provide images that confirm the presence of an acoustic neuroma.

Treatment :
Acoustic neuroma is a non-cancerous growth, which means it won’t spread to and damage other parts of the body. But it can continue to grow where it is, inside the skull.

It’s important to have it removed because although it grows slowly it can press on the nerves and part of the brain, causing permanent damage. This may result in hearing loss, poor balance and coordination, weakness in the muscles of the face and pain.

When a neuroma is suspected, diagnosis can be confirmed using a CT (computerised tomography) or MRI (magnetic resonance imaging) scan. These can also show the size and position of the tumour.

Most acoustic neuromas are surgically removed, after which many of the symptoms should disappear. This is more likely to be the case when the neuroma is small. Larger neuromas may have done irreversible damage to the brain and nerves before or during surgery.

Many patients have already lost a significant amount of hearing prior to surgery and this is not something that can be reversed although 40 per cent of patients who had tinnitus (ringing in the ears) noticed an improvement in that symptom after surgery.

This is why it’s best to treat an acoustic neuroma sooner rather than later. However, because they’re slow growing, only 1-2mm a year, very small neuromas may initially be just carefully monitored.

Stereotactic Radiotherapy (‘gamma knife’) may also be used to treat an acoustic neuroma.

Risk Factors:
The only known risk factor for acoustic neuroma is having a parent with the rare genetic disorder neurofibromatosis 2, but this accounts for only a minority of cases. A hallmark characteristic of neurofibromatosis 2 is the development of benign tumors on the acoustic nerves on both sides of your head, as well as on other nerves.

Neurofibromatosis 2 is known as an autosomal dominant disorder, meaning the mutation occurs on a nonsex chromosome (autosome) and can be passed on by just one parent (dominant gene). Each child of an affected parent has a 50-50 chance of inheriting it.

Other possible but unconfirmed risk factors for acoustic neuroma include:

*Exposure to loud noise
*Childhood exposure to low-dose radiation of the head and neck
*History of parathyroid adenoma, a benign tumor of the parathyroid glands in the neck
*Heavy use of cellular telephones

Copying & Support:

Dealing with the possibility of hearing loss and facial paralysis and deciding which treatment would be best for you can be quite stressful. Here are some suggestions you may find helpful:

*Educate yourself about acoustic neuroma. The more you know, the better prepared you’ll be to make good choices about treatment. Besides talking to your doctor and your audiologist, you may want to talk to a counselor or medical social worker. Or you may find it helpful to talk to other people who’ve had an acoustic neuroma and learn more about their experiences during treatment and beyond.
*Maintain a strong support system. Family and friends can help you tremendously as you go through this difficult time. Sometimes, though, you may find the concern and understanding of other people with acoustic neuroma especially comforting. Your doctor or a medical social worker may be able to put you in touch with a support group. Or you may find a real or virtual support group through the Acoustic Neuroma Association.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.

Resources:
http://www.bbc.co.uk/health/physical_health/conditions/acousticneuroma.shtml
http://www.nlm.nih.gov/medlineplus/acousticneuroma.html
http://en.wikipedia.org/wiki/Vestibular_schwannoma
http://www.mayoclinic.com/health/acoustic-neuroma/DS00803

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