Acoustic neuroma (or Vestibular Schwannoma) is a benign tumor of the the myelin forming cells called "Schwann cells" of the 8th cranial nerve, known as the acoustic nerve, (or more properly the vestibulocochlear nerve) just after it has left the brainstem, in the pontine angle; also at the point where the peripheral part of the nerve meets the brain part of the nerve called "Hensen's node". more...
Multiple names used for this type of tumor include acoustic neuroma, acoustic neuronoma and vestibular schwannoma because it attacks the 8th cranial nerve which branches in to the vestibular and acoustic; and under a microscope the tumor resembles schwann cells.
Associated symptoms are unilateral sensorineural hearing loss/deafness and vertigo. Additionally more than 80% of patients having acoustic neuromas have reported tinnitus. Larger tumors can compress local structures such as the facial nerve, and lead to local symptoms such as hydrocephalus.
If the tumor grows next to the brain stem and grows large enough, the brainstem may become compressed. Also associated with these nerves is the 7th cranial nerve; this nerve controls the muscles of the face, salivation, tearing, and taste. If a significantly large tumor develops it can involve the 5th cranial nerve controlling the sensation face and eyes.
While most cases occur sporadically, acoustic neuroma may be attributable to neurofibromatosis (type 2) in about 5% to 10% of the cases. If the tumor is caused by Neurofibromatosis a slightly different type of tumor grows, then the tumor often involves the whole nerve rather than particular sections of the nerve as does the schwannoma which can make treatment more a greater challenge. Also the tumor is classically bilateral with this syndrome.
Indicated treatments for acoustic neuroma include surgical removal and radiotherapy.
Because these neuromata grow so slowly, a physician may opt for conservative treatment beginning with an observation period. In such a case, the tumor is monitored by annual MRI to monitor growth. Records suggest that about 45% of acoustic neuromata do not grow detectably over the 3-5 years of observation. In rare cases, acoustical neuromata have been known to shrink spontaneously. Oftentimes, people with acoustic neruromata die of other causes before the neuroma becomes life-threatening. (This is especially true of elderly people possessing a small neuroma.)
Since the growth rate of an acoustic neuroma rarely accelerates, annual observation is essential.
Acoustic neuromata may cause either gradual or—less commonly—sudden hearing loss and tinnitus. However, the surgical and radiotherapy treatments are even more dangerous to the hearing in the affected ear.
The surgery is done by several approaches and is associated with high incidence of complications and quality of life issues - but it often removes the tumor without recurrence. The vestibular nerve is usually removed on the operated side, resulting in severe imbalance, vertigo and dizziness. However, vestibular function improves rapidly due to compensation by the other ear and other balance mechanisms. Steadiness may never be 100% of the pre-surgical level, but patients are usually walking in the first week after surgery. Surgery also has a risk to the facial nerve which is "monitored" during the surgery. Best results (normal or near normal facial function) are most likely with small acoustic neuromas. The larger the tumor, the higher the risks associated with removing it. Three surgical approaches are commonly used. The first is the translabyrinthine, which destroys hearing in the affected ear. Of the surgical approaches, it tends to be the fastest (less anesthesia time) and allows the most complete removal of the tumor (less chance of recurrence). The two other approaches (suboccipital and middle fossa) are hearing preservation approaches, which have a chance of preserving some or all of the hearing in the affected ear. However, all or most of the hearing in the operated ear is lost approximately 50% of the time. In addition, a number of medical reports indicate that surgically preserved hearing in the operated ear is often not stable, but may deteriorate significantly over a period of years. The hearing preservation approaches tend to require longer surgery, have a higher risk of recurrence and both require brain retraction, which carries a low risk of brain damage. Acoustic neuroma surgery is highly technically demanding, and patients are advised to seek out surgical teams with extensive experience.
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