Vestibular schwannoma

The first symptom in 90% of those with an acoustic neuroma is unexplained unilateral 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. In about 70 percent of cases there is a high frequency pattern of loss. The loss of hearing is usually subtle and worsens slowly, although occasionally a sudden loss of hearing may occur(i.e. sudden deafness). Hearing loss can vary from mild hearing loss to complete deafness.[10]

Unilateral tinnitus (ringing or hissing in the ears) is also a hallmark symptom of acoustic neuroma. 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.[11]

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. Balance or vertigo is the third most common symptom in patients with acoustic neuromas (50% incidence). The onset of these may be subtle, like disorientation in dark hallways, and be dismissed as age related decline. These symptoms tend to occur later in the development of the tumor.

Vestibular schwannoma patients sometimes complain of a feeling that their ear is plugged or "full".[11]

Larger tumors can press on the trigeminal nerve (CN V), causing facial numbness and tingling - constantly or intermittently. The facial nerve (CN VII) is rarely affected in the same way; however, due to its proximity to some structures of the inner and middle ear, it can be damaged during radiological treatment or surgical removal of the tumor, particularly in the case of large growths.

At the time some people learn they have an acoustic neuroma, they are also told that this tumor may involve the nerve that controls facial movement. However, it is much more common for treatment, rather than the tumor itself, to damage this nerve, leading to weakness or paralysis of the face. Taste, a sensation that reflects accurately sweet, sour, bitter and bland, is also a function of the facial nerve. Should any of the cranial nerves be damaged or need to be cut during surgery, it is sometimes possible for a neurosurgeon to microsuture the ends together; however, this is a new and very delicate specialist procedure, where long recovery times, incomplete healing and some permanent loss of function are to be expected.

Recurring headaches are an uncommon symptom, also tending to occur only in cases of larger tumors.

Large tumors may cause disabling and life-threatening symptoms.

Large tumors that compress the adjacent brainstem may affect other local cranial nerves. 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, clumsy gait and mental confusion. This can be a life-threatening complication requiring urgent treatment.[12]

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.[17]

Current studies suggest surgeons should observe small acoustic neuromas (those 1.5 cm or less).[7]

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.

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.[17] Surgery cannot restore hearing already lost.

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.[18]

During surgery, intraoperative neurophysiological monitoring of the facial, acoustic and lower cranial nerves can reduce the risk of injury.[19][20][21] In particular, following the 1991 NIH National institutes of Health Acoustic Neuroma Consensus Panel, the use of facial nerve monitoring has become a standard practice in the United States to reduce the risk of facial paralysis.[22]

With massive tumors that compress the brainstem and cerebellum, staged surgical approaches or subtotal surgical resection followed by stereotactic radiosurgery may reduce the risks to life, brain and cranial nerves.[23][24]

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.[25]

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.[26] For small tumors, a disadvantage lies in the risk of long-term postoperative headache.[27]

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.[27]

Middle cranial fossa surgical anatomy as demonstrated in a right cadaver temporal bone by Dr Jack M Kartush - view from above.

[28]

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.

Most patients present with tinnitus before treatment, and also have it after treatment. About one in 5 patients without tinnitus acquire it, and for about 2 in 5 with tinnitus it resolves or decreases.

While formerly, preservation of hearing during treatment was very unlikely, the newer techniques of microsurgery and stereotactic radiotherapy have enabled the preservation of functional hearing in the majority of cases. Overall, 60-66% of persons treated for AR preserve their hearing. Likelihood of preserving hearing is correlated with better hearing pre-treatment, and smaller size of tumor. If preservation of hearing is an important goal, the choice of surgical approach may be different. Even in those with functional hearing following surgery or radiotherapy, hearing may decline for years afterward.

Tumor regrowth occurs in 1-3% of cases treated surgically, and 14% in cases treated with radiation. 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. In case retreatment with surgery following radiation was required, the rate of complications was from 19.4%[29] to 27%[30] in two different studies, because the tumor tends to fuse to the nerve.

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.[31]

Taste disturbance and mouth dryness are frequent for a few weeks following surgery. In a few patients this disturbance is longer or permanent.

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 post-operative headaches have been more often associated with the sub-occipital/retrosigmoid approach than the translabyrinthine or middle fossa approaches.[32][33]

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 a computer.[34]

In rare cases where large tumors infringe on the brainstem which controls motor nerves, with or without surgery, paralysis or death can result. This occurs in less than 1% of large tumors.

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. This treatment has not been well studied and thus it is unclear if it is better than observation or surgery.[35]

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. Acoustic neuroma tumors have been completely eliminated by radiation treatments in almost no cases. In other words, radiation cannot remove the tumor like microsurgery would. 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 suggested against.

In single dose treatments, hundreds of small beams of radiation are aimed at the tumor. This results in a concentrated dose of radiation to the tumor and avoids exposure of surrounding brain tissues to the radiation. Many patients have been successfully treated this way. 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. 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.[36]