Acoustic neuroma | Symptoms, causes, tests and diagnosis

Acoustic neuroma



Acoustic neuroma is an uncommon, noncancerous (benign) and usually slow-growing tumor that develops on the main nerve leading from your inner ear to your brain. Because branches of this nerve directly influence your balance and hearing, pressure from an acoustic neuroma can cause hearing loss, ringing in your ear and unsteadiness.

Also known as vestibular schwannoma, acoustic neuroma usually grows slowly or not at all. However, in a few cases, it may grow rapidly and become large enough to press against the brain and interfere with vital functions.

Treatments for acoustic neuroma include regular monitoring, radiation and surgical removal.

Symptoms of the Acoustic neuroma

The signs and symptoms of acoustic neuroma develop from direct effects on the main nerve or from the tumor pressing on adjacent nerves, nearby blood vessels or brain structures.

As the tumor grows, it may be more likely to cause signs and symptoms, although tumor size doesn't always determine effects. It's possible for a small tumor to cause significant signs and symptoms.

You may experience signs and symptoms such as:
- Hearing loss, usually gradual — although in some cases sudden — and occurring on only one side or more pronounced on one side
- Ringing (tinnitus) in the affected ear
- Unsteadiness, loss of balance
- Dizziness (vertigo)
- Facial numbness and very rarely, weakness

In rare cases, an acoustic neuroma may grow large enough to compress the brainstem and threaten your life.

When to see your doctor
See your doctor if you notice hearing loss in one ear, ringing in your ear or trouble with your balance. Early diagnosis of an acoustic neuroma may help keep the tumor from growing large enough to cause serious consequences, such as total hearing loss or a life-threatening buildup of fluid within your skull.

Causes of the Acoustic neuroma

The cause of acoustic neuromas — tumors on the main balance nerves leading from your inner ear to your brain (eighth cranial 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, and currently there are no known risk factors for getting an acoustic neuroma.

Scientists do know the faulty gene is inherited in neurofibromatosis type 2, a rare disorder that usually involves the growth of tumors on balance nerves on both sides of your head (bilateral vestibular schwannomas).

Risk factors

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

Neurofibromatosis type 2 (NF2) is known as an autosomal dominant disorder, meaning that the mutation can be passed on by just one parent (dominant gene). Each child of an affected parent has a 50-50 chance of inheriting it.

Another possible risk factor that may be associated with acoustic neuroma includes childhood exposure to low-dose radiation of the head and neck.

Complications

An acoustic neuroma may cause a variety of permanent complications, including:
- Hearing loss
- Facial numbness and weakness
- Difficulties with balance
- Ringing in the ear

Large tumors may press on your brainstem, preventing the normal flow of fluid between your brain and spinal cord (cerebrospinal fluid). In this case, fluid can build up in your head (hydrocephalus), increasing the pressure inside your skull.

Tests and diagnosis

Because signs and symptoms of acoustic neuroma are likely to develop gradually and because symptoms such as hearing loss 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.

After asking questions about your symptoms, your doctor will conduct an ear exam. Your doctor may order the following tests:

- Hearing test (audiometry). In this test, conducted by a hearing specialist (audiologist), you 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 may also present various words to determine your hearing ability.
- Scans. Contrasted magnetic resonance imaging (MRI) or computerized tomography (CT) scans of your head can provide images that confirm the presence of an acoustic neuroma.
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