An acoustic neuroma is a noncancerous growth that develops on the eighth cranial nerve. Also known as the vestibulocochlear nerve, it connects the inner ear with the brain and has two different parts. One part is involved in transmitting sound; the other helps send balance information from the inner ear to the brain.
Acoustic neuromas -- sometimes called vestibular schwannomas or neurolemmomas -- usually grow slowly over a period of years. Although they do not actually invade the brain, they can push on it as they grow. Larger tumors can press on nearby cranial nerves that control the muscles of facial expression and sensation. If tumors become large enough to press on the brain stem or cerebellum, they can be deadly.
Acoustic Neuroma Symptoms
The early symptoms of an acoustic neuroma are often subtle. Many people attribute the symptoms to normal changes of aging, so it may be a while before the condition is diagnosed.
The first symptom is usually a gradual loss of hearing in one ear, often accompanied by ringing in the ear (tinnitus) or a feeling of fullness in the ear. Less commonly, acoustic neuromas may cause sudden hearing loss.
Other symptoms, which may occur over time, include:
- Problems with balance
- Vertigo (feeling like the world is spinning)
- Facial numbness and tingling, which may be constant or come and go
- Facial weakness
- Taste changes
- Difficulty swallowing and hoarseness
- Clumsiness or unsteadiness
It's important to see your doctor if you experience these symptoms. Symptoms like clumsiness and mental confusion can signal a serious problem that requires urgent treatment.
Acoustic Neuroma Causes
There are two types of acoustic neuroma: a sporadic form and a form associated with a syndrome called neurofibromatosis type II (NF2). NF2 is an inherited disorder characterized by the growth of noncancerous tumors in the nervous system. Acoustic neuromas are the most common of these tumors and often occur in both ears by age 30.
NF2 is a rare disorder. It accounts for only 5% of acoustic neuromas. This means the vast majority are the sporadic form. Doctors aren't certain what causes the sporadic form. One known risk factor for acoustic neuroma is exposure to high doses of radiation, especially to the head and neck.
Acoustic Neuroma Treatments
There are three main courses of treatment for acoustic neuroma:
- Radiation therapy
Observation is also called watchful waiting. Because acoustic neuromas are not cancerous and grow slowly, immediate treatment may not be necessary. Often doctors monitor the tumor with periodic MRI scans and will suggest other treatment if the tumor grows a lot or causes serious symptoms.
Surgery for acoustic neuromas may involve removing all or part of the tumor.
There are three main surgical approaches for removing an acoustic neuroma:
- Translabyrinthine, which involves making an incision behind the ear and removing the bone behind the ear and some of the middle ear. This procedure is used for tumors larger than 3 centimeters. The upside of this approach is that it allows the surgeon to see an important cranial nerve (the facial nerve) clearly before removing the tumor. The downside of this technique is that it results in permanent hearing loss.
- Retrosigmoid/sub-occipital, which involves exposing the back of the tumor by opening the skull near the back of the head. This approach can be used for removing tumors of any size and offers the possibility of preserving hearing.
- Middle fossa, which involves removing a small piece of bone above the ear canal to access and remove small tumors confined to the internal auditory canal, the narrow passageway from the brain to the middle and inner ear. Using this approach may enable surgeons to preserve a patient's hearing.
A newer, less invasive technique called total endoscopic resection enables surgeons to remove acoustic neuromas using a small camera inserted through a hole in the skull. This technique is offered only at major medical centers with specially trained surgeons. Initial studies show success rates similar to those with conventional surgery.
Radiation therapy is recommended in some cases for acoustic neuromas. State-of-the-art delivery techniques make it possible to send high doses of radiation to the tumor while limiting expose and damage to surrounding tissue.
Radiation therapy for this condition is usually delivered in one of two ways:
- Single fraction stereotactic radiosurgery (SRS), in which many hundreds of small beams of radiation are aimed at the tumor in a single session.
- Multi-session fractionated stereotactic radiotherapy (FRS), which delivers smaller doses of radiation daily, generally over several weeks. Early studies suggest multi-session therapy may preserve hearing better than SRS.
Both of these are outpatient procedures, which means they don't require a hospital stay. They work by causing tumor cells to die. The tumor's growth may slow or stop or it may even shrink, but radiation doesn't completely remove the tumor.
Other types of radiation therapy have also been used. Your doctor will explain your options to you.
Selecting the right treatment depends on a number of factors, including:
- Size of the tumor
- Whether the tumor is growing
- Your age
- Other medical conditions you may have
- Severity of your symptoms and their impact on your life