What is Acoustic Neuroma?
It is a type of primary intracranial tumor that affects the myelin-forming cells of vestibulocochlear nerve or CN VIII. It is a tumor on main nerve that leads from the inner ear to the brain and is benign in nature. The term ?vestibular schwannoma? incorporates the vestibular part of 8th cranial nerve, arising from the Schwann cells that are responsible for forming the myelin sheath of peripheral nervous system.
The condition is also known as Vestibular schwannoma.
Acoustic Neuroma Incidence
Nearly 3000 cases of this condition are diagnosed every year in United States having a prevalence of almost 1 in every 100000 worldwide. Vestibular schwannoma comprises 5% to 10% of all intracranial neoplasm types in adults. Incidence of the condition peaks in the 5th and 6th decades of life and both the sexes are equally affected.
Acoustic Neuroma Classification
Two different types of Vestibular schwannoma are known to exist: a sporadic form as well as a form that is associated with a condition known as neurofibromatosis type II or NF2. Neurofibromatosis type II is a type of inherited disorder that is characterized by growth of non-cancerous tumors in one?s nervous system. Among these tumors, the most common form is the acoustic neuroma which affects both ears by the age of 30.
Neurofibromatosis type II is a very rare disorder, and is responsible for only five percent of all acoustic neuroma cases. This indicates that the majority of AN cases are actually the sporadic form. There is widespread speculation among doctors as to what exactly gives rise to the sporadic form. A known risk factor that might trigger acoustic neuroma is an exposure to higher doses of radiation.
Acoustic Neuroma Causes
Acoustic neuromas are apparently caused by one malfunctioning gene on the chromosome 22. Generally, this gene manufactures a protein which helps in controlling the growth and development of Schwann cells that covers the nerves. The cause of production of this particular gene malfunction is not quite clear. Scientists are of the opinion that the defective gene is derived in almost 50% of the cases as a result of Neurofibromatosis type II. It is a rare disorder which involves development of tumors on vestibulocochlear nerve on the each side of head, also known as bilateral neuromas.
Acoustic Neuroma Symptoms
The earliest observable signs and symptoms of acoustic neuroma include:
- Ipsilateral sensorineural deafness or hearing loss
- Disturbed sensations of balance or ataxia
- Altered gait
- Vertigo along with nausea and vomiting
- Facial weakness
- Numbness
- Tingling
- Headaches
- Confusion
- Unsteadiness or clumsiness
- Difficulties in swallowing
- Hoarseness as well as pressure within the ear
All these symptoms can be associated with disruption of the normal functioning of the vestibulocochlear nerve. Apart from the above mentioned symptoms, more than 80% patients have reported signs of tinnitus. This generally involves a uni-lateral high-pitched ringing, an occasional hissing sound like that of a steam kettle or a machinery-like roaring.
Large tumors compressing adjacent brainstem might affect other cranial nerves at the locality. Paradoxically, the seventh cranial nerves are hardly involved pre-operatively. Loss of sensation within the face and mouth of the involved side might occur due to involvement of trigeminal nerve or CN V. The vagus and glossopharyngeal nerves are involved only in certain uncommon cases. However, their involvement might lead to instances of altered gag or other swallowing reflexes.
Increased intracranial pressure might result from larger tumors, and give rise to associated symptoms like:
- Headache
- Vomiting
- Altered consciousness
Loss of Hearing
Patients experiencing profound or severe unilateral hearing loss after the amputation of a disturbing acoustic neuroma tumor suffer from significant disability in a variety of situations like that of localizing sounds, hearing sounds from one?s deaf side, hearing sounds in presence of various background noises (both in noisy and quiet surroundings).
The perceived hearing disabilities might be even more in unilateral cases than in bilateral. Reports have also been documented which state that patients having unilateral hearing loss face difficulties during group discussions as well as dynamic listening situations which pose limited possibility for compensating for the listening problems by altering listening position.
Acoustic Neuroma Diagnosis
As the symptoms and signs of an acoustic neuroma are most likely to develop slowly, and since balance problems, tinnitus and hearing loss can indicate other middle or inner ear problems, detecting the tumor during the early stages might prove to be difficult for a doctor. Acoustic neuromas are often detected during screening for some other conditions.
Doctors initially ask questions about the symptoms and then recommend certain diagnostic tests:
Hearing tests or audiometry
In this test supervised by an audiologist or a hearing specialist, a patient is asked to wear earphones and listen to sounds directed to a single ear at a given time. The audiologist also produces numerous types of sounds having various tones and then repeats them in an almost barely audible level. The hearing ability of the patient is also checked by the presentation of various words.
Electronystagmography or ENG
This test evaluates vestibular function or balance by detecting signs of nystagmus or abnormal patterns of rhythmic eye movement that is frequently present with inner ear complications. It measures the involuntary eye movements of an individual along with balance in numerous ways.
Brainstem auditory evoked response (BAER)
The neurological and hearing functions of an individual are checked by this test. Electrodes and earlobes study the brain?s responses to various clicking sounds that can be heard through earphones, after which they are recorded on the graph.
Imaging Tests
Magnetic resonance imaging tests (MRI) or the Computerized Tomography (CT) Scans of the patient?s head can help in getting images that confirm presence of acoustic neuroma.
Acoustic Neuroma Differential Diagnosis
The differential diagnosis for acoustic neuroma includes taking into account several conditions that show similar symptoms, such as:
- Epidermoids
- Meningiomas
- Arachnoid cysts
- Lower cranial nerve schwannomas
Acoustic Neuroma Treatment
Depending on the age, the position and size of the tumor and one?s overall health, a patient of acoustic neuroma can choose from a number of different treatment options. The team of experts handling a case of an intracanalicular acoustic neuroma generally includes a neurosurgeon, an otolaryngologist, a radiosurgeon and an ENT (ear, nose, throat) surgeon.
Conservative treatment of Acoustic Neuroma
As these neuromas grow slowly, a physician might choose to monitor the condition regularly instead of immediately settling for an operational treatment. This is so because in many cases the risks commonly associated with a surgical procedure outweigh the threats posed by an acoustic neuroma. In these cases, annual MRI scans are used to monitor the growth of the tumor. This method is generally adapted while dealing with patients who are above 70 years of age. Records indicate that almost 45% of all neuromas do not grow to a significant degree over the 3 o 5 years of monitoring or observation. In some rare cases, these neuromas have also been known to minimize or shrink spontaneously. One numerous instances, patients of acoustic neuroma die of some other causes before their tumor becomes life-threatening. This is mostly true of elderly patients having a small neuroma. Annual observation is ideal for monitoring acoustic neuroma as their growth rate rarely accelerates.
Microsurgery
The tumor can be removed by using microsurgery. The patient is kept under the influence of general anesthesia and then the neuroma is removed by boring a hole or an incision through a patient?s skull.
If the neuroma is small, it can be removed completely in most cases. If it is large, a small portion of the tumor is commonly left behind for preserving the facial nerve. The small tumor which is left behind can then be regularly monitored by using MRI scans or be treated by employing radiosurgery.
Stereotactic radiosurgery
Vestibular schwannoma can be treated with stereotactic radiosurgery that delivers a precise and focused radiation dose to the affected area. A linear accelerator is used for this purpose. The term ?stereotactic? refers to the idea of locating a point by using three-dimensional coordinates. The procedure ensures that the tumor is bombarded with the maximum amounts of radiation possible without exposure to the surrounding tissue. The radiation can be given in one single dose or gradually delivered over numerous sessions. Stereotactic radiosurgery does not get rid of the tumor but its main aim is to stop a tumor from progressing further. The method can only be employed for small sized tumors or for the remnants of a small tumor after a surgery is done on large tumors.
Doctors perform stereotactic radiosurgery under local anesthetic. This means that a patient remains conscious throughout the length of the procedure even though his or her scalp is numbed. A lightweight metal framework is attached to the scalp and several scans are conducted which accurately pinpoint the location of the tumor. Then the tumor can be treated by using a definite beam of radiotherapy. There are little or no immediate side effects of this procedure and it will only require a few days to complete the treatment.
Other forms of radiotherapy include CyberKnife, proton therapy and gamma knife radiosurgery.
Translabyrinthine Approach
This method of surgery destroys hearing ability in an affected ear. Hence it is commonly used in cases where already the patients have poor speech discrimination capacity in affected ear. A tumor of any size might be removed by using this approach. No brain retraction is observed in this method and thus it is considered to be the best way to remove the neuroma. In patients of neurofibromatosis type 2 who are undergoing auditory brainstem implantation, the technique is employed as it gives easiest access to cochlear nucleus and lateral recess, where this device is implanted.
Middle Fossa and Suboccipital Retrosigmoid
These methods are hearing preservation techniques, attempting to preserve all or at least some of the hearing abilities in affected ears. Neurosurgeons frequently prefer the Suboccipital Retrosigmoid approach. Middle Fossa is commonly employed in cases where the tumor is generally less than 2 centimeters in dimensions.
The minimally invasive endoscopic surgery is a rather less common approach.
Acoustic Neuroma Complications
Although symptoms of this condition can seriously affect one?s normal life, serious complications from this form of neuroma are rare. If hearing is impaired, an individual might find his or her job is getting hampered. Loss of balance and severe dizziness can also affect one?s professional life and limit the activities one can perform.
Recurrence of a tumor after it has once been removed occurs in less than 5% of all cases, but is still a possibility. Hence the patient is required to be monitored at regular intervals with MRI or magnetic resonance imaging scans over several years regardless of the form of treatment one might have undergone.
A rather serious complication of acoustic neuroma is a condition referred to as the hydrocephalus. This occurs when the neuroma grows too large and causes pressure on the brainstem, which is the lowest portion of the brain connected to spinal cord. This hinders the CSF or cerebrospinal fluid from flowing between the brain and the spinal cord. The blockage can create pressure which can eventually build up inside the skull and might cause damage to the delicate tissues present in the brain. Excess CSF should be drained away in order to treat hydrocephalus. If not treated early, the hydrocephalus can lead to brain damage. In some rare cases, it can also be fatal.
Acoustic Neuroma Prognosis
Acoustic neuromas are not cancerous. These types of tumors do not metastasize or spread to the other areas of the body. Nevertheless, such a tumor may continue growing and causing pressure on other structures of the skull. Individuals having small or slow-growing tumors of this nature often do not require treatment. Recovery of hearing abilities is not possible through surgery or radiosurgery once it is lost.
After an acoustic neuroma surgery, the ear affected by the tumor loses its hearing ability. The patient may discuss his or her condition and choose to use a bone-anchored hearing aid that will help to divert sounds from the affected ear to the ear that is still in good health.
Surgery can also occasionally damage the facial nerve of a patient. This is due to the fact that acoustic nerve lies very close to one?s facial nerve and big-sized tumors are frequently stuck to it. The surgeon tries not to damage the facial nerve and leaves a small portion of a large tumor on facial nerve to preserve it. If the facial nerve is hampered during surgery, the patient may find that there is a drooping on any one side of the face. He or she may find it difficult to cover the eye on the weaker side of the face. The weaker side of the face will also have problems with drooling saliva and the speech will be less clear.
Symptoms will improve over a period of 6 to 12 months once assisted with physiotherapy. However, the some of the damages endured by the facial nerves might be permanent. It may also affect the eyes, making blinking or closing the eye difficult. This may lead to drying up of eyes and one might require artificial tears or an eye lubricant.
Acoustic Neuroma Support Groups
There are several support groups such as Acoustic Neuroma Association, Acoustic Neuroma Association of Canada (ANAC) and British Acoustic Neuroma Association (BANA) as well as many online forums that offer guidance and assistance to patients of acoustic neuroma and their families.
Acoustic Neuroma Pictures
Here are some images that show the mechanism and location of these tumors.
Picture 1 -?Acoustic Neuroma
Picture 2 -?Acoustic Neuroma Image
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Acoustic neuromas are benign tumors of the vestibulocochlear nerve that might lead to partial or complete hearing loss. The condition should not be left untreated as a progressed tumor can cause intracranial pressure and lead to further complications.
References:
http://www.nhs.uk/conditions/Acoustic-neuroma/Pages/Introduction.aspx
http://en.wikipedia.org/wiki/Vestibular_schwannoma
http://www.webmd.com/brain/acoustic-neuroma-causes-symptoms-treatments
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001782/
http://www.mayoclinic.com/health/acoustic-neuroma/DS00803
Source: http://www.healthinset.com/acoustic-neuroma-vestibular-schwannoma.html
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