|Acoustic Neuroma (swelling of 8th nerve, just under Facial nerve)|
Nikolopoulos and O'Donoghue reviewed 111 articles on acoustic neuroma treatment and stated that "well-designed comparisons between treatment methods do not exist, and therefore claims by clinicians favoring a particular treatment are unfounded" (2002). Similarly, studies of long-term quality of life show no significant difference (Robinett et al, 2014). We do not think that clinical wisdom can be completely discounted, but certainly the present situation seems to be that acoustic neuroma treatment is an art and no single treatment option is clearly superior.
According to Carlson et al (2015), about half of all patients are operated as soon as they are diagnosed, about 24% are radiated, and about 29% were observed. They also stated that in the US, there is a trend toward more observation and less surgery/radiation, mainly because tumors are being diagnosed earlier, when their size is smaller.
Over time, more acoustic neuromas are being diagnosed because there are far more MRI scans being done. There is a trend towards having smaller acoustics, and also towards having less aggressive acoustic neuromas over time. In other words, the playing field is changing and at present, we have a lot less aggressive tumors than in the past, due to sampling bias.
Medical Management of acoustic neuroma -- also called "wait/see" or "watchful waiting":
In practices with great experience, most acoustics less than 20 mm (i.e. 2 cm) in size are managed medically (Caye-Thomasen, 2016) -- i.e. with "watchful waiting". This to us appears to be a good strategy as well.
Between 29 and 50% of all acoustic neuromas are currently treated with medical management (Caye-Thomasen, 2016; Carlson et al, 2015; Stangerup and Caye-Thomasen, 2012). Medical management consists of periodic monitoring of the patient's neurological status, use of hearing aids when appropriate, and periodic imaging studies (such as MRI's). It is an appropriate method of management in some patients (Hoistad et al, 2001).
An "emerging" treatment for acoustics are medications.
There are a few medications that may slow growth or even cause shrinkage of acoustic neuromas.
Dilwali et al (2015) suggested that aspirin might reduce tumor growth of acoustic neuromas, and another study in 2014 (Kandathil et al), also reported "A significant inverse association was found among aspirin users and sVS growth (odds ratio [OR]: 0.50, 95% confidence interval [CI]: 0.29-0.85), which was not confounded by age or sex. ". MacKeith et al (2018) found no difference in aspirin intake (determined with a survey of 653 acoustic patients) between patients with stable acoustics and growing acoustics. So as of 2018, we have some disagreement in the literature. According to Dilwali, it is the Cox-2 receptor that mediates this effect, and thus one would expect a positive effect from any Cox-2 inhibitor that crosses into the brain. An odds ratio of 0.5 is not large - -i.e. aspirin is not a "magic bullet".
Bevacizumab, a VEGF-binding antibody, has previously been shown to induce tumour shrinkage and improve hearing in patients with NF2 (bilatral vestibular schwannomas), according to Alanin et al (2015). The risk of this treatment is somewhat high, and in fact one of the 12 patients in their study died from brain hemmorage.
At this writing (2016), we think it is reasonable for persons with acoustics being "watched" to consider taking daily aspirin, as the potential for harm is small. This is not the "standard of care" right now. Aspirin or similar drugs that inhibit Cox-2 (e.g. celebrex) need far more investigation, and one should also be cautious as these medications have well known adverse effects.
The tumors often grow very slowly (or not at all), less than 1 mm/year, and one may elect to follow a tumor with serial audiometry and/or MRI scans (Shin et al, 2000). In individuals of advanced age, a serious threat to life or bodily function from tumor growth may be judged unlikely in the remainder of a patient's expected lifespan, and for this reason, medical management may be elected (Perry et al, 2001). Once a tumor is diagnosed, a repeat scan is obtained at 6 months and then at yearly intervals (Perry et al, 2001).
This procedure has its own risks. Even when the tumor is not growing on MRI, there is a risk of losing useful hearing in this situation, making the individual no longer a candidate for hearing preservation type surgery. Somewhere between 10 and 43% of patients followed for about 2 years lose "useful" hearing (Warrick et al, 1999; Shin et al, 2000; Lin et al, 2005).
On the other hand, no matter what treatment procedure is used, surgical or not, in the long term, retention of "serviceable" hearing is very unlikely. The so-called "hearing preservation surgery" rarely preserves useful hearing, and hearing also tends to deteriorate fairly rapidly with time, with or without a tumor still being there. Because of this observation, some surgeons simply recommend taking out the entire 8th nerve when most convenient as this approach makes tumor recurrence very unlikely. In our opinion, this is should be a judgment call -- but not an unreasonable idea. A reasonable estimate is that over a year, about 75% of tumors will have visible enlargement, averaging 1.5 mm, and about 25% will not. Some variants grow much faster than others. In recent years, far more acoustics are being detected that are not growing rapidly, and the 1.5 mm/year statistic is likely much too high.
Wait/See patients are not necessarily doomed to go deaf -- Stangerup et al (2010) stated that "Most vestibular schwannoma patients with 100% speech discrimination at diagnosis maintain good hearing even after many years of observation. ". We agree with this.
In persons with neurofibromatosis, hearing is likely to remain stable in unoperated ears for about 1-2 years (Masuda et al, 2004).
Most people these days (i.e. in 2018) opt for a combination of watchful waiting followed by radiation treatment. This is covered in detail here.
|Very large acoustic neuroma (coronal view, the tumor is the large white blob). Source: Mayo Clinic Neuroscience Update.|
Surgical Treatment of acoustic neuroma
For larger tumors, cystic lesions, and neuromas with brainstem compression, according to the neurosurgeons, microsurgical resection in experienced neurosurgical centers is the preferred option (Unger et al, 2010). These are generally larger than 20 mm, but there is some "wiggle room" depending on where the tumor is located and the size of the individuals posterior fossa.
About half of all acoustic neuromas are presently treated with immediate surgery (Carlson et al, 2015). This number appears to us to be unreasonably high, as recent data suggests that acoustics grow more slowly than was previously appreciated, and also it is difficult to see the advantage of doing immediate surgery compared to a waiting process.
This fraction will likely decline over the next few decades as watchful waiting as well as use of GammaKnife/Cyberknife and other radiation based treatments grow. The figure above shows a large acoustic neuroma in which surgical management would generally be preferred. In most instances surgical removal of a large tumor is the preferred option because it prevents potentially fatal complications of tumor growth (although this would be very unusual). Surgery may theoretically enable "preservation" of hearing, although it is very rare that hearing is actually serviceable after surgery. Usually the surgery is done at an academic center by a team of surgeons including a neurotologist (a specialized otolaryngologist) and a neurosurgeon. There are several operative approaches.
Common surgical approaches to acoustic neuroma
(Image from Jackler R, Atlas of Neurotology and Skull Base Surgery (Mosby 1996, First edition, with permission).
|Temporal bone CT scan of man who had an acoustic removed via the retrosigmoid approach. Bone has been removed from a substantial portion of the posterior fossa. This page shows another image from the same patient, showing cochlear ossification.|
The translabyrinthine approach makes no attempt to preserve hearing, and does not open as much of the skull. This approach is generally a good one in terms of little collateral damage (Springborg et al, 2012), but of course, would not be appropriate for someone with substantial hearing. There is no expectation that hearing will be preserved. It is not a good approach for large tumors as visibility is poor.
The middle fossa approach (not shown above), can theoretically preserve hearing, but like the retrosigmoid, the approach is intrinsically more dangerous than the translab, as it involves retraction of the brain, and also more prone to complications.
On the internet, there are some surgeons that propose endoscopic treatments for acoustic neuroma. With the idea that acoustic neuroma surgery is somehow similar to "band-aid" abdominal surgery, a "scope" is inserted through a hole drilled in the skull and all work is done through a tiny hole. While it is possible to do this, we think it is foolish. What one gains from a smaller incision, in our opinion, is lost by the added risk of poor exposure and visualization. Do you really want somone trying to operate on a very delicate structure such as the 8th nerve, through a tiny hole ? Disasters certainly occur in surgeries with wide exposure -- why would one want to risk your brain function in order to have a smaller scar and shorter recovery period ? Interestingly, some of these surgeon's have lost their medical license because of fraud related to these surgeries. As of 2017, we think you should stay away from doctors who propose endoscopic treatment of the inner ear. This advice not only includes both acoustic neuroma and surgery on other ear conditions, such as superior canal dehiscence or perilymph fistulae.
Compared to radiosurgery, the primary advantage of conventional surgery is avoidance of late complications associated with radiation of neighboring structures. This is a reasonable consideration which, in our opinion, makes conventional surgery advantageous when the patient is a reasonable surgical risk.
Each of these surgical approaches has advantages and disadvantages that must be considered in selecting an optimal approach. Surgical treatment where the brain is exposed is nearly always performed by a team of surgeons, usually including a neurotologist and a neurosurgeon. Most patients are admitted to the hospital a day before the operation. After surgery, they spend a night in a monitored unit. Most are discharged from the hospital within 4-6 days after surgery, and return to work is usually possible in 6 weeks. MRI's are usually obtained at 1 and 5 years to detect residual or recurrent tumor. Total or near total (95%) removal of the tumor is advised (Sanna et al, 2002). Careful follow up with MRI is advised to detect recurrence. Nodular or progressive enhancement in the internal auditory canal may represent regrowth (Brors et al, 2003).
Tumors that extend into the labyrinth itself (i.e. "intracochlear schwannomas") may not be removed by the "retrolab" approach to tumors, and may recur. There are also many significant complications that can result from surgery that should be considered (see below).
With respect to hearing preservation surgery, while of course this is certainly desirable, unfortunately the chance of hearing being preserved after acoustic neuroma surgery is slight. Nedzelski and colleagues recently reported that only about 16% of patients had "serviceable" hearing in the follow up interval after "hearing preservation surgery". (Lin et al, 2005). While hearing may be "preserved" immediately after surgery, it usually deteriorates in most within a few years. Peng and Wilkinson (2016), on the other hand, stated that " microsurgery, including the middle fossa approach, may provide excellent hearing outcomes, particularly when a small tumour has begun to cause hearing loss." There is a "catch-22" problem here. Small tumors are doing very little damage, so one might want to just let them grow. On the other hand, a surgeon might argue that it is too late to save hearing once the damage is done. We ourselves favor the conclusion of the Nedzelski group -- that hearing preservation is possible but unlikely after surgery on the 8th nerve.
Subtotal resections of acoustic neuromas, unsurprisingly, are associated with far greater frequency of "recurrence", to be exact, 13 times (Jacob et al, 2016). One would wonder if the term "recurrence" is the right one, as the surgeon here just leaves some tumor behind. Jacobs et al state that "Maximal surgical resection should be the goal in VS microsurgery." Still, one can reasonably argue that these tumors take so long to grow, and that most of the damage has already been done at the time of the initial resection, this gives surgeon leeway to judge whether the risks to the patient from the surgery are commensurate with the risks to the patient from regrowth. In other words, your surgeon should have good judgement.
At the author's clinical practice in Chicago Illinois, it is suggested that prospective operative candidates primarily consider safety and the probability of complications when considering surgery or radiotherapy (i.e. GammaKnife or CyberKnife). If one has serviceable hearing, and there is no other danger of waiting (such as needing a bigger operation), one might reasonably simply wait until hearing becomes unserviceable (i.e. useless) before proceeding with surgery or radiation. Here the procedure would be periodic hearing tests, and less frequent MRI scans. The frequency of testing is mainly determined by the rate of change in the measures, but about every year for hearing testing and about once/year (or more) for MRI scanning is usually appropriate. If there is no change after the first 6 months, it is reasonable to move the rechecks out farther -- to once/yearly, or sometimes once every few years. If the tumor is very small (i.e. 5 mm or less), then studies might reasonably be spaced out further out. It is most cost-effective to follow hearing and nystagmus (with Frenzel goggles), and do an MRI least frequently of all.
We have some patients in our practice with acoustic neuromas that we have followed for 20 years. Their tumor has grown very slowly, but as their hearing is unaffected and the tumor is not large, both we and the patient have decided to just keep watching. On the other hand, we have also had a few where their tumor enlarged substantially over a few years, and we sent them on to our surgical colleagues.
Medical management, surgery and radiotherapy methods of managing acoustic tumors all seem reasonable at this writing, with the choice depending on individual factors. Medical management is almost always the best strategy for small tumors. Surgical management has the advantage that it "gets it over with quickly", but normally dizziness is much worse shortly after tumor removal (El-Kashlan et al, 1998). Radiotherapy is less acutely stressful, but it can delay resolution of dizziness.
The usual dogma is that patients with acoustics, prior to surgery, do not need vestibular rehabilitation. Evidence for this is that in persons with small acoustic neuromas, conservatively managed, there is a small reduction in balance associated with a slightly higher than control risk of falls. (Low Choy et al, 2016).
On the other hand, in most instances (but certainly not all), acoustic neuroma surgery results in complete loss of vestibular function on the operated side. Gamma knife treatment also is associated with substantial decline in vestibular function (Wackym, 2004). Patients frequently experience vertigo and imbalance post-surgery (Levo et al, 2004; Tufarelli et al, 2007). Vestibular rehabilitation may speed recovery from this deficit. Unless there already is complete loss of vestibular function prior to surgery or radiation (as documented on ENG or VHIT), we think it is best that the patient who is planning to have acoustic neuroma surgery visit a vestibular physical therapist to make sure that there is a "good fit" and to learn the basic procedures, and for the individual to begin a weekly program of PT for 1-2 months following discharge. It is important that the otologic surgeon who performs the operation be involved with the therapy as in some situations (i.e. patients with CSF leak), therapy should be delayed.
Suggestions have been made that patients with acoustic neuroma have a "preemptive strike" on their vestibular function, to speed up their return to work after surgery. In other words, spread the dizziness over a longer period. Attempts have been made to use low dose intratympanic gentamicin prior to surgery. This appears to be a bad idea for several reasons. First, not everyone develops unilateral vestibular loss, or for that matter, any vestibular loss at all after surgery. Why would you want to make injury a sure thing ? Second, adding a toxin onto surgery increases the risk of hearing loss. (Tjernstrom et al, 2016)
Piazza and others recently suggested that in the elderly, the following algorithm should be followed: If the acoustic protrudes less than 1 cm into the cerebellopontine angle, an MRI should be repeated in one year. If the growth rate is < 2 mm/year, the patient should be observed. If greater than this, offered surgery. We are a little puzzled about the 2 mm/year growth rate criterion, as one would think that if a tumor went from 1 to 3 mm total, it would still be very small, and one should still wait. Of course, a tumor that grew 10 mm/year, we would think should have something done to stop its growth. We are a little worried about the idea that one should "offer surgery" in older persons who are otherwise functioning well, as the mortality of surgery in those > 65 is 13-fold higher (see later section on the complication of "death"). We would think "offer radiosurgery" if possible, might be a better strategy.
Sylvester et al (2017) reported that in the elderly (defined as 65+), looking at 4137 total patients, there were much higher frequences of medical complications (e.g. heart attacks, strokes, bleeding), than in the non-elderly. Complications related to the surgery -- such as CSF leak, meningitis and facial nerve injury (see below)-- were identical.
According to Piazza, for tumors that protrude > 1 cm into the CP angle, and patients in good general health should be offered surgery. Patients in poor general health should be offered radiosurgery (Piazza et al, 2003). We think that this strategy is a little too much in favor of surgery, and instead we would usually advise patients to avoid surgery or radiation until there was a reasonable expectation of impending damage to structures other than the inner ear. We also would stratify by age.
Stangerup et al (2008) stated that "After comparing the hearing results of hearing preservation surgery and of radiation therapy with those of 'wait and scan' management, it appears that, in vestibular schwannoma patients with a small tumour and normal speech discrimination, the main indication for active treatment should be established tumour growth."
Surgical treatment of acoustic neuroma has a substantial risk. Overall, the risk of death from acoustic neuroma surgery is about 0.5 to 2 percent. Unexpected post-operative complications occur in roughly 20 percent with more complications occurring in elderly and infirm individuals and those with large tumors (Kaylie et al, 2001). Complications, ordered from rare to frequent, are listed.
A review of acoustic neuroma surgery suggested that CSF leak (9.4%) and meningitis (1.5%) are the most common complications (Slattery et al, 2001). El-Kashlan et al (1998) reported that dizziness from unoperated acoustic neuroma's is generally mild as damage progresses slowly and is handled with compensation. On the other hand, immediately after surgical removal, most patients report "severe vertigo and disequilibrium".
Cerebellar injury impairs recover from surgery for acoustic neuroma:
MRI scan from person who had acoustic neuroma removed via retrolab approach, and with refractory dizziness. On the right side of the picture (left side of head), there is a black area where there was damage to the cerebellum, presumably associated with the surgery. Another scan showing cerebellar damage following acoustic neuroma surgery. This type of injury will most likely be accompanied by permanent imbalance due to the combination of a cerebellar injury and loss of inner ear function on the left. Tumor operated in 1961. There is clear cerebellar damage on the left side of the cerebellum (right side of picture). Residual acoustic neuroma as well as cerebellar damage, in this patient who had surgery in the remote past.
In a review of results of 258 patients operated via the translabyrinthine approach, stroke or cerebellar injury occurred in 1.1%. Cerebellar injury can occur due to traction as well as due to injury to branches of the anterior inferior cerebellar artery (Hegarty et al, 2002). Images of cerebellar traction injury are shown above. These patients generally have very prominent oculomotor signs (e.g. nystagmus) and persistent (e.g. lifelong) imbalance.
There can also be traction injuries to the temporal lobe, after middle fossa route surgery.
Death following acoustic neuroma surgery
There is overall a 0.5 percent incidence of death due to acoustic neuroma surgery. The elderly (> 65) have 13.18 times as much mortality as the non-elderly (Sylvester et al, 2017) .Thus if you are over 65 -- maybe surgery is not the best choice for you. There is usually the gamma knife option - -which has far less risk of death.
Discharge to long-term care (1.2%), to short-term rehabilitation (4.4%) are also possibilities (Barker et al, 2003). Thus, there is roughly a 1.7% chance of death or long term nursing care being required after acoustic neuroma surgery.
The odds are better if one chooses a "high volume" hospital and surgeon. So if you are planning to be operated -- think to yourself -- is it worth it to me to take a (roughly) one chance in 50 of being dead or requiring long-term nursing care ?
Other complications include CSF leak in 7.8%, meningitis in 1.6%.
Facial weakness of various degrees appeared in most, but severe weakness with House-Brackman scores of V-VI at 1 year occurred in 6% (Mass et al, 1998).
In the literature, surgeons often use the term "serviceable" hearing (e.g. Lin et al, 2005), meaning literally that hearing is of some service, or "better than nothing". Note that they are not talking here about "restoring" hearing to normal -- what is dead is dead. Also, realistically, surgery (or radiation) is a destructive procedure. A procedure that removes some nerve (with tumor) is unlikely to improve hearing. The best one might hope for would be a small reduction in hearing (after surgery), followed by stability.
With that in mind, of course, hearing generally gets worse after acoustic neuroma surgery. Keep in mind also that audiograms are somewhat subjective, there is such a thing as a placebo response, and reported results may sometimes mainly be wishful thinking.
Turning to the data:
Wiet and others have reported results in 500 cases (Wiet et al, 2001). Overall success at retaining useful hearing was 27%, with considerably better results obtained when operating via the middle-fossa approach.
Hearing in the operated ear often deteriorates over time to a greater extent than the unoperated ear, even without recurrent tumor (Chee et al. 2003). The percent of persons with "serviceable hearing" may deteriorate by 25% in the late post-operative period. This has been variously attributed to scarring, fibrosis, or microhemmorages during operation.
Over the long term, very few patients retain serviceable hearing (Lin et al, 2005). Some authors have suggested that given the modest hearing that is salvaged in the very few patients who are candidates for hearing sparing surgery, that hearing preservation as an objective of acoustic neuroma surgery is not worthwhile (Tos et al, 1988). Our view is that it is occasionally worth attempting, but one's expectations should be realistic. Hearing occasionally improves for the middle fossa approach (Stidham and Roberson, 2001). The middle fossa approach has more risk to one's brain and other aspects than other approaches.
One might preserve hearing when hearing is good, and the tumor is small. Then the patient must choose between the risk of sitting tight and surgery (or radiation). In other words, a gamble.
One would not be likely to preserve hearing without any change when the hearing is good, and the tumor is big. Here, the odds are stacked against one. It would seem likely though that people who already have moderate hearing impairment, would do worse than persons with excellent hearing, if one considers the net hearing after the surgery is over. This is just common sense.
This is simple stuff -- balance deteriorates after acoustic surgery because the surgery damages or removes remaining function in the vestibular nerve (Levo et al, 2004; Tufarelli et al, 2007). Tufarelli and associated reported that 10% of 459 patients judged their imbalance as disabling, and 73% felt that they had at least moderate oscillopsia (trouble seeing with head moving).
It has been our experience that over the long term (i.e. 2 years), balance generally returns to near normal, but persons who have other deficits such as visual disturbances (e.g. cataract), sensory loss (e.g. neuropathy), brain damage (e.g. cerebellar or brainstem damage due to the tumor or surgery), or poor adaptation (e.g. due to advanced age) may never obtain complete return of balance.
At a meeting at the ANA (acoustic neuroma association), the author of this page participated in a 2-hour session and interviewed 8 patients who had persistent vertigo. As a general rule, patients who had vertigo 2 years following surgery, had had a mixture of a cerebellar injury and total vestibular loss, associated with a difficult surgery (usually for a 4cm + tumor). The MRI scan of two patients are shown above. As a general rule, patients who have lost both inner ear function (from the acoustic), and substantial cerebellar function (from the surgery or acoustic), will have an enduring loss of balance.
Immediately after surgery, most patients have vertigo. The timing and prognosis of this vertigo depends on the reason and associated damage to the cerebellum (if any). A detailed discussion of dizziness, vertigo and imbalance, pre and post surgery can be found in this lecture handout.
Significant headache can occur following acoustic neuroma surgery (reviewed by Driscoll and Beatty, 1997). The incidence is very variable among surgeons and also depends on the choice of approach, but an overview of the literature suggests an incidence of about 20-35%. This compares with an incidence of about 8% after radiosurgery.
Schessel et al (1996) observed and documented adherence of neck muscles to the dura after craniotomy and reported a dramatic decrease in headache in patients who had craniotomy with replacement of the bone flap. Similarly, Harner also noted a drop in headache when cranioplasty with methyl methacrylate was used instead of craniotomy alone (Harner et al, 1995). The mechanism here is thought to be traction on the dura by movement of neck muscles. Many patients with this syndrome note aggravation by coughing or straining.
Schessel et al (1996) suggested that patients having surgery via the retrosigmoid approach had significantly higher frequency of headache than those who had the translabyrinthine approach. Several other groups have found a similar pattern. Schaller and Bauman (2003) noted severe headaches requiring daily medication and accompanied by a feeling of incapacity in 34% of patients at 3 months following retrosigmoid surgery. They found that these headaches were associated with aseptic meningitis and furthermore that they were associated with use of fibrin glue and drilling in the posterior aspect of the internal auditory canal. They suggested that prevention of postoperative headache may be accomplished by replacement of bone flap at the end of surgery, use of duraplastic instead of direct dural closure, and avoidance of the use of fibrin glue or extensive drilling of the posterior aspect of internal auditory canal.
Currently there is little information about incidence of headache using the middle fossa approach, but the few series available suggest a rather low incidence (Driscoll et al, 1997).
Management of post-operative headache utilizes analgesics, muscle relaxants, antidepressants and anticonvulsants, in a way similar to migraine management. Migraine abortive agents, however, and specific prophylactic drugs for migraine are not recommended in most instances. Nevertheless, a recent report found that sumatriptan (a migraine drug) improved headache in 9/10 patients with post-surgical headaches. This probably reflects the fact that migraine is an extremely common health condition that worsens with any type of head pain.
Persistent incisional pain may occur from entrapment of the occipital nerve or from formation of an occipital neuroma. Massage, local heat, and analgesics may help. Occipital nerve blocks (such as is done in the pain clinic) may also be beneficial.
Another mechanism that have been suggested is that bone dust trapped within the intracranial cavity may cause a protracted inflammatory response resulting in chronic headache (Driscoll, 1997). MRI images sometimes show dural enhancement (the membrane covering the brain "lights up") and CT images may show calcification along the brainstem (Schaller and Bauman, 2003). This sort of headache should not respond to blocking of scalp nerves (as is done in the pain clinic) and this procedure may be of some diagnostic use. In these patients, logically treatment might include anti-inflammatory agents and possibly corticosteroids. Narcotic analgesics are occasionally indicated.
No standards exist regarding patient follow-up following complete acoustic neuroma resection. On average though, 3 to 6 scans is common over a follow-up period of about 5 years. (Lee and Isaacson, 2005).
A person with an acoustic neuroma might desire a cochlear implant. Logic would suggest that this is generally a foolish endeavor, although there are reports to the contrary (Lassaletta et al, 2016) . Acoustics are nerve tumors, or in electrical terms, disorders of wiring. Cochlear implants stimulate the part of the ear prior to the wiring - -they affect the microphone. Thus, one would expect that a cochlear implant would generally be ineffective in someone whose cochlear nerve has already been damaged by a tumor. In situations where there is one deaf ear, a "BAHA" is the logical choice.
Nevertheless, one might give it a try anyway if an acoustic tumor is present in the only hearing ear or after surgery to remove bilateral acoustic neuromas. Belal (2001) reported that cochlear implantation is possible only if there is an intact cochlear nerve (as shown by a positive response to promontory stimulation), and if the implantation is done at the time of acoustic tumor removal, before the cochlea ossifies.