All you need to know about Acoustic neuroma.
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Here we come with Acoustic neuroma today!
What is Acoustic neuroma?
Acoustic neuroma is also known as
- acoustic neurilemoma
- acoustic neurinoma
- fibroblastoma, perineural
- neurinoma of the acoustic nerve
- neurofibroma of the acoustic nerve
- schwannoma of the acoustic nerve
- Vestibular schwannoma
Acoustic neuroma, a tumor that grows on the main (vestibular) nerve leading from your inner ear to your brain, is non-cancerous and typically slow-growing. Your balance and hearing are directly affected by branches of this nerve, and pressure from an acoustic neuroma can cause hearing loss, ringing in your ear, and unsteadiness.
Typically, acoustic neuroma emerges from the Schwann cells that cover this nerve and progresses slowly or not at all. It can rarely develop quickly and become too large to strain the brain and interfere with vital functions.
Regular testing, radiation, and surgical removal are included in therapies for acoustic neuroma.
Acoustic neuromas affect women more often than men. Most cases of acoustic neuroma develop in individuals between the ages of 30 and 60. Although quite rare, they can develop in children. Acoustic neuromas are estimated to affect about 1 in 100,000 people in the general population. Racial differences have been reported in which Black, Hispanic, and Asian Americans have relatively lower rates of acoustic neuroma diagnosis than White Americans.
Approximately 2,500 new patients are diagnosed each year. The incidence has risen in the last several years, which some researchers attribute to the greater frequency in which small tumors are recognized. However, many individuals with small acoustic neuromas may remain undiagnosed, making it difficult to determine its true frequency in the general population.
In 0.7–1.0 individuals per 100,000 population, clinically diagnosed acoustic neuromas occur. The incidence may be increasing, a result of the increasing frequency of the more common use of MRI to diagnose tiny tumors. The frequency of accidental acoustic neuromas was indicated by a 2005 study by Lin et al to be 2 in 10,000 individuals. In a higher percentage of elderly patients, diligent autopsy studies may detect tiny vestibular schwannomas, indicating that many acoustic neuromas never become clinically evident.
What are the types of Acoustic neuroma?
There are 2 types of acoustic neuromas:
- Unilateral acoustic neuromas. Only one ear is affected by this kind. It is the type of acoustic neuroma that is most common. At any age, this tumor will grow. It most commonly occurs between the ages of 30 and 60. The consequence of nerve damage caused by environmental factors can be an acoustic neuroma. There has been no environmental factor shown to cause acoustic neuromas.
- Bilateral acoustic neuromas. Both ears are affected by this form and are inherited. A genetic problem called neurofibromatosis-2 (NF2) triggers it.
What are the causes of Acoustic neuroma?
For no apparent cause (spontaneously), most instances seem to occur. There have been no specific risk factors reported for the development of these tumors.
A number of possible risk factors for acoustic neuroma have been studied, including previous exposure to head and neck radiation (as in the treatment of some cancers) or prolonged or continuous exposure (as in an occupational environment) to loud noise. In order to determine the exact cause and risk factors associated with acoustic neuroma, the study is ongoing.
Acoustic neuromas occur in a small subset of cases as part of a rare condition known as type II neurofibromatosis. Acoustic neuromas affecting both ears at once (bilateral) are typically associated with this unusual genetic condition. (Choose ‘neurofibromatosis’ as your search word in NORD’s Rare Disease Database for more information on this disorder.)
From a type of cell known as the Schwann cell, an acoustic neuroma occurs. These cells form an insulating layer, including the eighth cranial nerve, overall the nerves of the peripheral nervous system (i.e., nerves outside the central nervous system). The cochlear branch, which transmits sound to the brain, and the vestibular branch, which transmits balance data to the brain, separate the eighth cranial nerve into two branches. In the vestibular segment of the eighth cranial nerve, most acoustic neuromas occur. Since these tumours consist of Schwann cells and typically appear on the eighth cranial nerve vestibular section, many doctors prefer the use of the term vestibular schwannoma. In the medical literature, however, the term acoustic neuroma is still used more frequently.
What are the symptoms of Acoustic neuroma?
These are the most common symptoms of acoustic neuroma:
- Hearing loss on one side, can’t hear high-frequency sounds
- The feeling of fullness in the ear
- A ringing in the ear (tinnitus), on the side of the tumor
- Balance problems or unsteadiness
- Facial numbness and tingling with possible, though rare, paralysis of a facial nerve
- Headaches, clumsy gait, and mental confusion
- Some people may not have any associated (asymptomatic) symptoms, especially those with small tumors. Even small tumors, however, may cause important symptoms or physical findings, depending on their location.
- Slow-growing tumors that can ultimately cause a number of symptoms by rubbing against the eighth cranial nerve are acoustic neuromas. The initial symptom in approximately 90 percent of patients is hearing loss in one ear (the ear affected by the tumor). Usually, hearing loss is incremental, but it can be abrupt in some extreme cases. Hearing loss can also fluctuate (worsen and then improve) in some situations. Ringing in the ears, a condition known as tinnitus, or a sensation of fullness in the affected ear may accompany hearing loss. In certain situations, people affected can have trouble processing speech that is disproportionate to the amount of hearing loss.
- Acoustic neuromas, including unsteadiness, can also cause dizziness and balance problems. In rare cases, prior to apparent hearing loss, dizziness or balance issues can occur. Since these tumors typically develop very slowly, these balance issues can also be compensated for by the body.
- Acoustic neuromas, although slow-growing, may gradually become big enough to strain against neighboring cranial nerves. Though rare, facial weakness or paralysis, facial numbness or tingling, and swallowing problems include symptoms arising from the involvement of other cranial nerves. Facial numbness or tingling may be continuous or (intermittent) it may come and go.
- Acoustic neuromas can develop large enough to push against the brain stem in some patients, preventing cerebrospinal fluid from flowing normally between the brain and the spinal cord. This fluid will collect in the skull, resulting in a condition called hydrocephalus, which induces brain tissue pressure and results in a number of symptoms, including headaches, decreased ability to control voluntary movements (ataxia), and mental confusion. Headaches may also occur in the absence of hydrocephalus, which may be the first symptom of acoustic neuroma in some extreme cases. An untreated acoustic neuroma that presses on the brain may cause life-threatening complications in very rare cases.
What are the risk factors of Acoustic neuroma?
A parent with the rare genetic condition neurofibromatosis type 2 is the only documented risk factor for acoustic neuroma. Yet type 2 neurofibromatosis accounts for just around 5 percent of cases of acoustic neuroma.
The existence of noncancerous tumors on the balance nerves on both sides of your head as well as on other nerves is a hallmark feature of neurofibromatosis type 2.
Form 2 (NF2) neurofibromatosis is classified as an autosomal dominant condition, meaning only one parent (dominant gene) can pass on the mutation. There is a 50–50 risk for each offspring of an infected parent to inherit it.
What are the compliments of Acoustic neuroma?
An acoustic neuroma may cause a variety of permanent complications, including:
- Hearing loss
- Facial numbness and weakness
- Difficulties with balance
- Ringing in the ear
Large tumors can press on your brain stem, preventing the normal flow of fluid (cerebrospinal fluid) between your brain and your spinal cord. In this situation, fluid (hydrocephalus) will build up in your brain, thus increasing the pressure inside your skull.
How is Acoustic neuroma diagnosed?
Since signs of these tumors mimic other diseases of the middle and inner ear, they can be hard to identify. The ear evaluation and hearing tests are preliminary diagnostic procedures. The location and scale of the tumor are determined using computerized tomography (CT ) and magnetic resonance imaging ( MRI) scans. Early diagnosis provides the best chance for good therapy.
- A hearing test (audiometry): The first test conducted to diagnose acoustic neuroma is typically the hearing function test, which tests how well the patient hears sounds and speech. When wearing earphones attached to a computer that tracks reactions and tests hearing functions, the patient listens to sounds and speech. Increased “pure tone average” (PTA), increased “speech reception threshold” (SRT) and decreased “speech discrimination” (SD) may be recorded in the audiogram.
- Brainstem auditory evoked response (BAER): This test is conducted in certain patients as a reaction to clicks or tones to provide information on brain wave activity. Although wearing electrodes on the scalp and earlobes and headphones, the patient listens to these sounds. The electrodes pick up the brain‘s reaction to these sounds and record them.
- Scans of the head: Magnetic resonance imaging (MRI) is used to validate the diagnosis if other tests indicate that the patient may have an acoustic neuroma. Instead of x-rays, MRI uses magnetic fields and radio waves, and computers to construct accurate brain images. It depicts visual “slices” of the brain that can be combined to create an image of the tumor in three dimensions. Injected into the patient is a contrast dye. If there is an acoustic neuroma, more dye than natural brain tissue can suck up the tumor and show distinctly on the scan. In the internal auditory canal, the MRI normally reveals a thick “enhancing” (bright) tumor.
What is the treatment for Acoustic Neuroma?
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 treatments 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/suboccipital, 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.
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 exposure 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
- The severity of your symptoms and their impact on your life
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