Vestibular Schwannoma | |
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Bilateral schwannomas in a patient with neurofibromatosis 2
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Classification and external resources | |
Specialty | oncology |
ICD-10 | D33.3 |
ICD-9-CM | 225.1 |
ICD-O | M9560/0 |
DiseasesDB | 100 |
MedlinePlus | 000778 |
eMedicine | ent/239 |
MeSH | D009464 |
A vestibular schwannoma is a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve (8th cranial nerve). A type of schwannoma, this tumor arises from the Schwann cells responsible for the myelin sheath that helps keep peripheral nerves insulated.[1] Approximately 3,000 cases are diagnosed each year in the United States. Most recent publications suggest that the incidence of acoustic neuromas is rising because of advances in MRI scanning. Studies in Denmark published in 2004 showed an annual incidence of 17.4 per million. Most cases are diagnosed in people between the ages of 30 and 60, and men and women appear to be affected equally.[2]
It is also commonly called an acoustic neuroma, although this term is technically a misnomer: the tumor rarely arises from the acoustic division of the vestibulocochlear nerve, and it is really a schwannoma rather than a tumor of actual nerve tissue (the literal meaning of the somewhat ambiguous term "neuroma").
The primary symptoms of vestibular schwannoma are unexplained unilateral hearing loss and tinnitus, and vestibular (disequilibrium) symptoms. Treatment of the condition is by surgery or radiation, and often results in substantial or complete hearing loss in the affected ear. Observation (non-treatment) over time also usually results in hearing loss in the affected ear.
Signs and symptoms
Early symptoms are easily overlooked, sometimes mistaken for the normal changes of aging or attributed to noise exposure earlier in life, often delaying diagnosis. The first symptom in 90% of those with an acoustic neuroma is unilateral hearing loss (a reduction in hearing in one ear), often accompanied by ringing in the ear called tinnitus. The loss of hearing is usually subtle and worsens slowly, although occasionally a sudden loss of hearing can occur. There may be a feeling of fullness in the affected ear.
Since the balance portion of the eighth nerve is where the tumor arises, unsteadiness and balance problems or even vertigo (the feeling like the world is spinning), may occur during the growth of the tumor. The remainder of the balance system sometimes compensates for this loss, and, in some cases, no imbalance will be noticed. Larger tumors can press on the trigeminal nerve, causing facial numbness and tingling - constantly or intermittently. Although the facial nerve may be compressed by the tumor, it is unusual for patients to experience weakness or paralysis of the face from an acoustic neuroma, although this may occasionally occur. Tumor related increase of intracranial pressure may cause headaches, clumsy gait and mental confusion. This can be a life-threatening complication requiring urgent treatment.[3]
Large tumors that compress the adjacent brainstem may affect other local cranial nerves. Paradoxically, the 7th cranial nerves are rarely involved pre-operatively; involvement of the trigeminal nerve (CN V) may lead to loss of sensation in the involved side's face and mouth. The glossopharyngeal and vagus nerves are uncommonly involved, but their involvement may lead to altered gag or swallowing reflexes.
Larger tumors may lead to increased intracranial pressure, with its associated symptoms such as headache, vomiting, and altered consciousness.
Hearing loss
Hearing loss is the most common disability in patients with acoustic neuromas and affects all age groups. Hearing loss can vary from no or mild hearing loss to complete deafness (also known as profound hearing loss or single-sided deafness. [4]
Acoustic neuromas typically cause sensorineural hearing loss, meaning there is damage to the inner ear (cochlea) or nerve pathways from the inner ear to the brain. It involves a reduction in sound level, speech understanding and hearing clarity.
Tinnitus
Tinnitus is the perception of sound in the ears or head where no external source is present. Some call it "ringing in the ears" or "head noise". Not all patients with tinnitus have acoustic neuroma and not all AN patients have tinnitus. Most of them do however, both before and after treatment.[5]
Pressure in the Ears
Acoustic neuroma patients sometimes complain of a feeling that their ear is plugged or "full".[5]
Facial weakness or paralysis
At the time most people learn they have an acoustic neuroma, they are also told that this tumor may involve the nerve that controls facial movement. The functioning of facial muscles is taken for granted, and a patient may find it difficult to grasp the connection between a benign growth on the nerve of hearing and any compromise of the facial nerve. People scarcely appreciate the exquisite musculature of the face that allows them to express themselves through speech and emotional expression—from wide-mouthed laughter to scowling disapproval. The eyes blink and are precisely moistened, or tear voluntarily after receiving a message from the brain that more tears are needed. Taste, a sensation that reflects accurately sweet, sour, bitter and bland, is also a function of the facial nerve.
Cause
The cause of acoustic neuromas is usually unknown; however there is a growing body of evidence that sporadic defects in tumor suppressor genes may give rise to these tumors in some individuals.[medical citation needed] Other studies have hinted at exposure to loud noise on a consistent basis. One study has shown a relationship between acoustic neuromas and prior exposure to head and neck radiation, and a concomitant history of having had a parathyroid adenoma (tumor found in proximity to the thyroid gland controlling calcium metabolism).[medical citation needed] There are even controversies on hand held cellular phones. Whether or not the radiofrequency radiation has anything to do with acoustic neuroma formation, remains to be seen. To date, no environmental factor (such as cell phones or diet) has been scientifically proven to cause these tumors. The Acoustic Neuroma Association (ANA) does recommend that frequent cellular phone users use a hands free device to enable separation of the device from the head.[6]
Although there is an inheritable condition called Neurofibromatosis Type 2 (NF2) which can lead to acoustic neuroma formation in some people, most acoustic neuromas occur spontaneously without any evidence of family history (95%).[7] NF2 occurs with a frequency of 1 in 30,000 to 1 in 50,000 births. The hallmark of this disorder is bilateral acoustic neuromas (an acoustic neuroma on both sides).
Diagnosis
Advances in scanning and testing have made possible the identification of small acoustic neuromas (those still confined to the internal auditory canal). Routine auditory tests may reveal a loss of hearing and speech discrimination (the patient may hear sounds in that ear, but cannot comprehend what is being said). Pure tone audiometry should be performed to effectively evaluate hearing in both ears. The clinical criteria for follow up testing for AN is a 15 dB differential in thresholds between ears for three consecutive frequencies.
Magnetic resonance imaging (MRI) using Gadolinium as an enhancing contrast material is the preferred diagnostic test for identifying acoustic neuromas. The image formed clearly defines an acoustic neuroma if it is present and this technique can identify tumors measuring only a few millimeters in diameter.
An auditory brainstem response test (a.k.a. ABR) is a much more cost effective screening alternative to MRI for those at low risk of AN. This test provides information on the passage of an electrical impulse along the circuit from the inner ear to the brainstem pathways. An acoustic neuroma can interfere with the passage of this electrical impulse through the hearing nerve at the site of tumor growth in the internal auditory canal, even when the hearing is still essentially normal. This implies the possible diagnosis of an acoustic neuroma when the test result is abnormal. An abnormal auditory brainstem response test should be followed by an MRI.
When an MRI is not available or cannot be performed, a computerized tomography scan (CT scan) with contrast is suggested for patients in whom an acoustic neuroma is suspected. The combination of CT scan and audiogram approach the reliability of MRI in making the diagnosis of acoustic neuroma.[dubious ][8]
Pathophysiology
Acoustic neuromas normally develop gradually over a period of years, roughly 1–2 mm each year. 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. Vital functions to sustain life can be threatened when large tumors cause severe pressure on the brainstem and cerebellum. 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).[9]
Treatment
There are three treatment options available to a patient. These options are observation, microsurgical removal and radiation (radiosurgery or radiotherapy). Determining which treatment to choose involves consideration of many factors including the size of the tumor, its location, the patient's age, physical health and current symptoms.[8] About 25% of all acoustic neuromas are treated with medical management consisting of a periodic monitoring of the patient's neurological status, serial imaging studies, and the use of hearing aids when appropriate. One of the last great obstacles in the management of acoustic neuromas is hearing preservation and/or rehabilitation after hearing loss. Hearing loss is a both a symptom and concommitant risk, regardless of the treatment option chosen.
A diagnosis of NF2 related bilateral acoustic neuromas creates the possibility of complete deafness if the tumors are left to grow unchecked. Preventing or treating the complete deafness that may befall individuals with NF2 requires complex decision making. The trend at most academic U.S. medical centers is to recommend treatment for the smallest tumor which has the best chance of preserving hearing. If this goal is successful, then treatment can also be offered for the remaining tumor. If hearing is not preserved at the initial treatment, then usually the second tumor, in the only-hearing ear, is just observed. If it shows continued growth and becomes life-threatening, or if the hearing is lost over time as the tumor grows, then treatment is undertaken. This strategy has the highest chance of preserving hearing for the longest time possible.[10]
Observation
Since acoustic neuromas tend to be slow-growing and are benign tumors, careful observation over a period of time may be appropriate for some patients. When a small tumor is discovered in an older patient, observation to determine the growth rate of the tumor may be indicated if serious symptoms are not present. There is now good evidence from large observational studies that suggest many small tumors in older individuals do not grow, thus allowing tumors with no growth to be observed successfully. If the tumor grows, treatment may become necessary. Another example of a group of patients for whom observation may be indicated includes patients with a tumor in their only hearing or better hearing ear, particularly when the tumor is of a size that hearing preservation with treatment would be unlikely. In this group of patients, MRI is used to follow the growth pattern. Treatment is recommended if either the hearing is lost or the tumor size becomes life-threatening, thus allowing the patient to retain hearing for as long as possible.[11]
Over a period of 10 years of observation with no treatment, 45% of patients with small tumors (and therefore minimal symptoms) lose functional hearing on the affected side; this percentage is considerably higher than that for patients actively treated with hearing-preserving microsurgery or radiosurgery.
Surgery
The goals of surgery are to control the tumor, and preserve function of the involved nerves (i.e. those involved in facial musculature and hearing). Preservation of hearing is an important goal for patients who present with functional hearing.[11]
Microsurgical tumor removal can be done at one of three levels: subtotal removal, near total removal or total tumor removal. Many tumors can be entirely removed by surgery. Microsurgical techniques and instruments, along with the operating microscope, have greatly reduced the surgical risks of total tumor removal. Subtotal removal is indicated when anything further risks life or neurological function. In these cases the residual tumor should be followed for risk of growth (approximately 35%). If the residual grows further, treatment will likely be required. Periodic MRI studies are important to follow the potential growth rate of any tumor. Near total tumor removal is used when small areas of the tumor are so adherent to the facial nerve that total removal would result in facial weakness. The piece left is generally less than 1% of the original and poses a risk of regrowth of approximately 3%.
There are three main surgical approaches for the removal of an acoustic neuroma: translabyrinthine, retrosigmoid/sub-occipital and middle fossa. The approach used for each individual person is based on several factors such as tumor size, location, skill and experience of the surgeon, and whether hearing preservation is a goal. Each of the surgical approaches has advantages and disadvantages in terms of ease of tumor removal, likelihood of preservation of facial nerve function and hearing, and post-operative complications [12]
Translabyrinthine approach
The translabyrinthine approach may be preferred by the surgical team when the patient has no useful hearing, or when an attempt to preserve hearing would be impractical. The incision for this approach is located behind the ear and allows excellent exposure of the internal auditory canal and tumor. Since the incision goes directly through the inner ear, this results in permanent and complete hearing loss in that ear. Many patients with medium to large ANs have no functional hearing in the ear anyway, so this may not be an issue. The surgeon has the advantage of knowing the location of the facial nerve prior to tumor dissection and removal. Any size tumor can be removed with this approach and this approach affords the least likelihood of long-term postoperative headaches.[13]
Retrosigmoid/sub-occipital approach
The incision for this approach is located in a slightly different location. This approach creates an opening in the skull behind the mastoid part of the ear, near the back of the head on the side of the tumor. The surgeon exposes the tumor from its posterior (back) surface, thereby getting a very good view of the tumor in relation to the brainstem. When removing large tumors through this approach, the facial nerve can be exposed by early opening of the internal auditory canal. Any size tumor can be removed with this approach. One of the main advantages of the retrosigmoid approach is the possibility of preserving hearing. For small tumors, a disadvantage lies in the risk of long-term postoperative headache.[14]
Middle fossa approach
This approach is in a slightly different incision location and is utilized primarily for the purpose of hearing preservation in patients with small tumors, typically confined to the internal auditory canal. A small window of bone is removed above the ear canal to allow exposure of the tumor from the upper surface of the internal auditory canal, preserving the inner ear structures.[14]
Radiation
Another treatment option for an acoustic neuroma is radiation. Stereotactic radiation can be delivered as single fraction stereotactic radiosurgery (SRS) or as multi-session fractionated stereotactic radiotherapy (FSR). Both techniques are performed in the outpatient setting, not requiring general anesthesia or a hospital stay. The purpose of these techniques is to arrest the growth of the tumor causing the tumor to die, which is called necrosis. This treatment has not been well studied and thus it is unclear if it is better than observation or surgery.[15] All types of radiation therapy for acoustic neuromas may result in "tumor control" in which the tumor cells die and necrosis occurs. Tumor control means that the tumor growth may slow or stop and, in some cases, the tumor may shrink in size. In almost no cases have acoustic neuroma tumors been completely eliminated by radiation treatments. In other words, radiation does not remove the tumor like microsurgery can. Tumors under 2.5 - 3.0 cm, without significant involvement of the brainstem, are more favorable for radiation treatment. Side effects can occur when the brainstem is irradiated and in some cases of large tumors, radiation is contraindicated.
In single dose treatments, many hundreds of small beams of radiation are aimed at the tumor. This results in a high dose of radiation to the tumor and very little to any surrounding brain structures. Many patients have been treated this way with high success rates.[clarification needed][medical citation needed] Facial weakness or numbness, in the hands of experienced radiation physicians, occurs in only a small percent of cases. Hearing can be preserved in some cases.
The multi-dose treatment, FSR, delivers smaller doses of radiation over a period of time, requiring the patient to return to the treatment location on a daily basis, from 3 to 30 times, generally over several weeks. Each visit lasts a few minutes and most patients are free to go about their daily business before and after each treatment session. Early data indicates that FSR may result in better hearing preservation when compared to single-session SRS.
Radiated patients require lifetime follow-up with MRI scans. Follow-up after SRS and FSR typically involves an MRI scan and audiogram at six months, one year, then yearly for several years, then every second or third year indefinitely to make sure the tumor does not start to grow again. Patients should understand there have been rare reports of malignant degeneration (a benign tumor becoming malignant) after radiotherapy. In some cases the tumor does not die and continues to grow. In those instances, another treatment is necessary - either microsurgery or sometimes another dose of radiation.
Studies are beginning to appear for the other modalities.[clarification needed] All of the techniques use computers to create three dimensional models of the tumor and surrounding neural structures. Radiation physicists then create dosimetry maps showing the level of radiation to be received by the tumor and the normal tissues. Surgeons, radiation therapists and physicists then modify the dosimetry to maximize tumor doses and minimize radiation toxicity to surrounding normal tissues. Treatments generally last 30–60 minutes. Just like for surgery, the experience of the team in treating acoustic neuromas with all modalities (surgery and radiation) can affect outcomes.
There are a multitude of studies supporting short-term (<5 yrs.) and longer-term (over 10 yrs.) tumor control with radiation. Unfortunately, as is the case with microsurgical studies, most have inconsistent follow-up to draw definitive conclusions.[16]
Complications
The overall rate of complications is about 20% for surgical removal, the most common being cerebrospinal fluid leakage.
Cancers (radiotherapy)
There are documented incidences of new malignant gliomas and malignant progression of ANs after focused radiotherapy using either SRS or FRT for benign intracranial lesions.
Tumor regrowth
Tumor regrowth occurs in 1-3% of cases treated. Likelihood of regrowth is proportional to the bulk of tumor remaining in case of surgery, and inversely proportional to radiation dose in case of radiotherapy.
Facial nerve damage
In the 2012 Acoustic Neuroma Association patient survey, 29% of the respondents reported facial weakness or paralysis, some of which were pre- and some were post-treatment. This represents a significant improvement from the 1998 Acoustic Neuroma Association patient survey of post-treatment acoustic neuroma patients, which revealed that at the time they completed the survey, only 59% were satisfied with the appearance of their face. Treatment for an acoustic neuroma may damage the facial nerve – either with surgery or radiation. It is usually possible, however, to preserve some degree of facial function even in cases where the nerve is extensively involved. For those with partial nerve regeneration, in whom some facial weakness remains, non-surgical facial rehabilitation therapies also may be beneficial.[17]
Headaches
Head pain is expected in most patients immediately after acoustic neuroma surgery (acute phase) because of the incision, variations in cerebrospinal fluid pressure, muscle pain, or even meningitic pain. It typically responds to appropriate medications and resolves within several weeks. Headache that persists for months or even years after surgery (chronic phase) can be debilitating and may be an under-appreciated complication of acoustic neuroma treatment. In patients who experience chronic headaches, the pain often persists for prolonged periods of time, and does not always respond well to various medical and surgical treatments. The exact prevalence and causes of chronic postoperative headache (POH) are elusive. After surgical treatment of acoustic neuroma, the reported incidence of headache in the 2012 Acoustic Neuroma Association patient survey has ranged from 0% to 35% depending on the type of surgical approach, technique used and reporting interval since surgery. Frequent and severe POHs have been more often associated with the sub-occipital or retrosigmoid approaches than the translabyrinthine or middle fossa approaches.[18][19]
Balance
Essentially everyone who has been treated for an acoustic neuroma experiences difficulty with balance and/or dizziness to some degree. For some, this instability may be mild and noticeable only in certain circumstances, such as ambulating with head movements, or walking in the dark. For others, there may be difficulty returning to work, or even performing regular daily activities such as driving, shopping, house work and even working on your computer. [20]
See also
References
- ^ "Acoustic Neuroma". NHS Choices. Retrieved 30 August 2013.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma Basic Overview". ANA Patient Information Booklets: 3.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma Basic Overview". ANA Patient Information Booklets: Page 2.
- ^ Acoustic Neuroma Association (January 2013). "Hearing Loss Rehabilitation For Acoustic Neuroma Patients". ANA Patient Information Booklets: Page 1.
- ^ a b Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Page 4.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Page 10.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Page 3.
- ^ a b Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Page 5.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma Basic Overview". Acoustic Neuroma Association Patient Information Booklets: page 1.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Pages 10–11.
- ^ a b Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Page 6.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Page 7.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Pages 7–8.
- ^ a b Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Page 8.
- ^ Muzevic, D; Legcevic, J; Splavski, B; Cayé-Thomasen, P (16 December 2014). "Stereotactic radiotherapy for vestibular schwannoma.". The Cochrane database of systematic reviews 12: CD009897. doi:10.1002/14651858.CD009897.pub2. PMID 25511415.
- ^ Acoustic Neuroma Association (November 2013). "Acoustic Neuroma - Basic Overview". ANA Patient Information Booklets: Pages 8–10.
- ^ Acoustic Neuroma Association (February 2012). "Facial Nerve and Acoustic Neuroma - Possible Damage and Rehabilitation". ANA Patient Information Booklets: Page 1.
- ^ Acoustic Neuroma Association (June 2012). "Headache Associated with Acoustic Neuroma Treatment". ANA Patient Information Booklets: Pages 1–2.
- ^ Acoustic Neuroma Association (2012). "ANA Patient Survey".
- ^ Acoustic Neuroma Association (November 2011). "Improving Balance Associated with Acoustic Neuroma". ANA Patient Information Booklet.
- Notes
Text has been adapted from the following ANA Patient Information Booklets of the Acoustic Neuroma Association:
- Acoustic Neuroma Basic Overview
- Hearing Loss Rehabilitation For Acoustic Neuroma Patients
- Facial Nerve and Acoustic Neuroma - Possible Damage and Rehabilitation
- Headache Associated with Acoustic Neuroma Treatment
- Improving Balance Associated with Acoustic Neuroma
- ANA Patient Survey
External links
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