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Acoustic Neuroma
By peace | November 21, 2006
An acoustic neuroma (sometimes termed a neurolemmoma or schwannoma) is a benign (non-cancerous) tissue growth that arises on the eighth cranial nerve leading from the brain to the inner ear. This nerve has two distinct parts, one part associated with transmitting sound and the other sending balance information to the brain from the inner ear. These pathways, along with the facial nerve, lie adjacent to each other as they pass through a bony canal called the internal auditory canal. This canal is approximately 2 cm. (0.8 inches) long and it is here that acoustic neuromas originate from the sheath surrounding the eighth nerve. The facial nerve provides motion of the muscles of facial expression.
Acoustic neuromas usually grow slowly over a period of years. They expand in size at their site of origin and when large can displace normal brain tissue. The brain is not invaded by the tumor, but the tumor pushes the brain as it enlarges. The slowly enlarging tumor protrudes from the internal auditory canal into an area behind the temporal bone called the cerebellopontine angle. The tumor now assumes a pear shape with the small end in the internal auditory canal. Larger tumors can press on another nerve in the area (the trigeminal nerve) which is the nerve of facial sensation. Vital functions to sustain life can be threatened when large tumors cause severe pressure on the brainstem and cerebellum part of the brain. Tumors are typically described as small (less than 1.5 cm.), medium (1.5 cm. to 2.5 cm.) or large (more than 2.5 cm.).
Approximately 3000 cases are diagnosed each year in the United States with an incidence of about 1 in 100,000. Incidence peaks in the fifth and sixth decades and both sexes are affected equally.
Earliest symptoms of acoustic neuromas include unilateral sensorineural hearing loss/deafness, disturbed sense of balance and altered gait, vertigo with associated nausea and vomiting, and pressure in the ear, all of which can be attributed to the disruption of normal vestibulocochlear nerve function. Additionally more than 80% of patients have reported tinnitus (most often a uniteral high-pitched ringing, sometimes a machinery-like roaring or hissing sound, like a steam kettle).
Large tumors that compresses the adjacent brainstem may affect other local cranial nerves. Involvement of the 7th cranial nerve (facial nerve) may lead to facial weakness, sensory impairment, and impairment of glandular secretions; involvement of the 5th cranial nerve (trigeminal nerve) may lead to loss of taste and loss of sensation in the face and mouth. Involvement of the 9th and 10th cranial nerves are uncommon, but may lead to altered gag or swallowing reflexes.
Even larger tumors may lead to increased intracranial pressure, with its associated symptoms such as headache, vomiting, and altered consciousness.
Causes
Acoustic neuromas may be inherited (passed from parent to child). It is believed that acoustic neuromas form when one special gene stops working. Sometimes it is not known what causes acoustic neuromas.
Signs and Symptoms
The signs and symptoms of an acoustic neuroma are caused as the tumor grows. The symptoms are usually only in one ear or on one side of your face. As the tumor gets larger, it presses on nerves and other tissues nearby in the brain.
Early signs of an acoustic neuroma:
- Hearing loss
- Tinnitus (ringing in your ear)
- Sounds are distorted (fuzzy) and off key
Later signs and symptoms as the acoustic neuroma gets bigger:
- Difficulty tasting things
- Diplopia (double vision)
- Dizziness
- Eyes do not blink as often as they should and do not make enough tears
- Face may become weak or paralyzed (cannot move) on one or both sides
- Face may also hurt on one or both sides
- Headaches
- Trouble swallowing and speaking
- Tongue begins to twitch without control
- Tiredness (fatigue), confusion, and finally coma.
Are Acoustic Neuromas hereditary?
No. Although there is an inheritable condition called neurofibromatosis which can lead to acoustic neuroma formation in some people, most acoustic neuromas occur spontaneously without any evidence of an inheritable pattern.
How often do Acoustic Neuromas occur?
Asymptomatic acoustic neuromas have been found during autopsy in less than one in one-hundred or perhaps as few as .01% of the general population. Acoustic neuromas large enough to cause hearing loss and other symptoms occur in about one person in 100,000. Most acoustic neuromas are diagnosed in patients between the ages of 30 and 60.
Important Points To Know About an Acoustic Neuroma:
1. An acoustic neuroma is a benign tumor.
2. It is usually slow growing and expands at its site of origin.
3. The most common first symptom is hearing loss in the tumor ear only.
4. The cause is unknown.
5. A large tumor pushes on the surface of the brain but does not grow into the brain tissue.
6. Continued tumor growth can be life threatening.
7. The treatment options are observation, surgical removal or radiation.
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