Acoustic Schwannomas

Definition

Definition of Acoustic Schwannomas
Acoustic neuromas are intracranial, extra-axial tumors that arise from the Schwann cell sheath investing either the vestibular or cochlear nerve. As acoustic neuromas increase in size, they eventually occupy a large portion of the cerebellopontine angle. Acoustic neuromas account for approximately 80% of tumors found within the cerebellopontine angle. The remaining 20% are principally meningiomas. In rare cases, a facial nerve neuroma, vascular tumor, lipoma, or metastatic lesion is found within the cerebellopontine angle.

Symptoms

Symptoms of Acoustic Schwannomas
The signs and symptoms of acoustic neuroma develop from the tumor pressing on the adjacent nerves, or 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.

Signs and symptoms may include:

1. Hearing loss, usually gradual - although in some cases sudden - and occurring on only one side or more pronounced on one side
2. Ringing (tinnitus) in the affected ear
3. Unsteadiness, loss of balance
4. Dizziness (vertigo)
5. Facial numbness and weakness

Causes

Causes of Acoustic Schwannomas
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).

Diagnosis

Diagnosis of Acoustic Schwannomas
An acoustic neuroma can be difficult to diagnose. This is because the symptoms often develop gradually and can therefore be difficult to spot. Symptoms such as dizziness and hearing loss can also be attributed to a number of other conditions, such as Ménière's disease (a rare disorder that affects the inner ear).

If your GP suspects that you may have an acoustic neuroma, you will be referred to a hospital or clinic for further testing.

Complications

Complications of Acoustic Schwannomas
An acoustic neuroma may cause a variety of complications, including:

1. Permanent hearing loss
2. Facial numbness and weakness
3. Difficulties with balance and clumsy gait

Treatment

Treatment of Acoustic Schwannomas
There are three options for managing an acoustic neuroma: periodic monitoring, radiation and surgical removal.

1. Monitoring: If you have a small acoustic neuroma that isn't growing or is growing slowly and causes few or no signs or symptoms, you and your doctor may decide to monitor it, especially if you're an older adult or otherwise not a good candidate for treatment. Your doctor may recommend that you have regular imaging and hearing tests, usually every six to 12 months, to determine whether the tumor is growing and how quickly. If the scans show the tumor is growing or if the tumor causes progressive hearing loss or other difficulties, you may need to undergo treatment.
2. Stereotactic Radiosurgery: Stereotactic radiosurgery, such as gamma-knife radiosurgery, enables doctors to deliver radiation precisely to a tumor without making an incision. The doctor attaches a lightweight headframe to your numbed scalp. Using imaging scans, your doctor pinpoints the tumor and then plots where to apply the radiation beams. The purpose of radiosurgery is to stop the growth of a tumor. It's generally an option if you have a small tumor or if you're not a candidate for surgery. It may also be used for residual tumors - portions of a tumor that traditional brain surgery can't remove without damaging brain tissue. It may take weeks, months or years before the effects of radiosurgery become evident. Your doctor will monitor your progress with follow-up imaging studies and hearing tests. Risks of radiosurgery include hearing loss, facial weakness and balance problems.
3. Surgical Removal: There are several techniques for removing an acoustic neuroma, but in general the goal of surgery is to remove the tumor, preserve the facial nerve to prevent facial paralysis and preserve hearing as much as possible. Performed during general anesthesia, surgery for an acoustic neuroma involves removing the tumor through the inner ear or through an incision in your skull. You may need to stay in the hospital from four to six days after the surgery, and recovery may take six weeks or more.