|
The management of acoustic neuromas has been revolutionized by the physicians and scientists at the House Ear Clinic. In the early 1960's acoustic neuromas were treated utilizing a suboccipital approach without the aid of an operating microscope. At that time the mortality for acoustic neuroma removal in the State of California was 40%. At that time, Dr. William House, a young associate of his brother Howard, was able to diagnose a small acoustic neuroma. The patient was referred to a neurosurgeon and the neurosurgeon recommended that the tumor be observed - a common course of management at that time.
The tumor grew relatively rapidly and was then operated by the suboccipital approach without the aid of magnification. Unfortunately, this young fireman died of the surgical procedure. This had a profound effect upon Dr. William House and at that time he began doing dissections in the laboratory with the aid of magnification and subsequently developed first the middle cranial fossa and then the translabyrinthine approach for removal of acoustic neuromas.
The use of the operating microscope soon became standard practice for all approached for removal of acoustic neuroma. The mortality rate rapidly fell to less than 1% and preservation of facial nerve function became the rule rather than the exception. More recently, preservation of hearing has also become a realistic goal in acoustic tumor surgery.
At the House Ear Clinic and Institute, a surgical team manages these tumors. The team consists of a neurotologist, a neurosurgeon, an internist, the anesthesiologist and then the entire support team of surgical intensive care and clinical nurses who care for the patient during their surgery and hospitalization. We believe that this team approach is important in that it adds the combined expertise of several disciplines to improve patient outcomes.
At the House Ear Clinic all current modalities used for the treatment of acoustic neuromas are employed. In general, we favor surgical removal of the tumor but may employ stereotactic x-ray therapy when indicated. Our indication for stereotactic x-ray therapy are the same as those recommended by the consensus conference of the National Institute of Health, namely a relatively small tumor that is growing in an elderly patient or one whose medical condition is such that it is deemed inadvisable to perform surgical removal. We recommend surgery, however, for the majority of our patients.
return to top of page »
SURGICAL THERAPY
Surgery for acoustic neuromas has been performed since the early 1900's. The initial successes were few and far between by the early pioneering neurosurgeons who treated this problem. The past twenty years have witnessed an astounding improvement in our abilities to successfully deal with these tumors while preserving the neurological function of the patient.
Since the early 1960's, surgeons at the House Ear Clinic have been at the forefront of innovations in the surgical treatment of acoustic neuromas. Many of the most significant advances in surgical approaches to the skull base have originated from House Ear Clinic surgeons. The treatment of acoustic neuromas and other brain tumors is constantly undergoing refinement and evaluation at the House Ear Clinic. Because of this commitment to "cutting edge" and quality patient care, the House Ear Clinic has become the largest referral center for acoustic neuromas world wide. Each year, more than 200 patients with acoustic neuromas are treated by members of the House Ear Clinic team; more than at any other center in the world.
In contemporary surgical treatment of these tumors, the vast majority of patients lead a normal life following their surgery. The two main concerns that patients typically have is preservation of facial nerve function and of hearing. The facial nerve exits the brain stem and is anatomically in a position adjacent to the vestibulocochlear nerve. The anatomical relationships of the nerves to the structures of the inner ear and the brain stem can be seen in the section on anatomy. Preservation of facial nerve function is extremely important because of its cosmetic implications. Normal movement of the face on each side is controlled by the facial nerve. Any disruption leads to a loss of normal muscular tone and movement in that side of the face. Our results at the House Ear Clinic with facial nerve preservation are greater than ninety-eight percent (98%) in terms of preserving the anatomical continuity of the nerve.
Preserving anatomical continuity of the nerve means that the nerve is intact and was not disrupted by the surgical procedure. Even with an intact nerve, the functional abilities of the nerve may not be complete. However, results from our series over the years have shown excellent results in terms of functional outcome of the facial nerve. In a recently reviewed series of over three hundred and eighty (380) patients who underwent a middle fossa-type approach at the House Ear Clinic, ninety-five percent (95%) of these patients maintained excellent facial nerve function after surgery. Only five percent (5%) suffered minor weakness of the facial nerve function. Preservation of facial nerve function is dependent to some degree on the size of the tumor that is removed. The influence of tumor size on facial nerve functional outcomes is illustrated by another recent study from our group observing a recently treated group of over one hundred and ninety (190) patients via a translabyrinthine approach with tumors measuring greater than 3cm in size. In this group of patients, eighty percent (80%) had an acceptable functional outcome. (House-Brackmann grades 1-3)However, only fifty-five percent (55%) of patients had an excellent outcome (House-Brackmann grades 1-2). The aforementioned series of over 380 patients all had tumors smaller than 2cm in diameter. This comparison is a good illustration of the influence of tumor size on outcome.
One of the major recent focuses of acoustic neuroma surgery is the preservation of hearing. Major strides have been made in recent years in terms of improving the results of hearing preservation with surgery. Much like facial nerve results, the size of tumor is an influential factor. Also important is how well the patient hears prior to surgery. Hearing is determined by a test called an audiogram. This is performed by an audiologist. If the results of the audiogram indicate that the hearing level is sufficient to indicate a reasonable chance of success with saving the hearing during surgery, then a surgical approach is selected that is designed to save hearing. Otherwise, it may be advisable to choose a treatment approach that sacrifices hearing in order to obtain a total resection of the tumor.
Most patients with adequate pre-operative hearing levels have small tumors which are mostly confined to the internal auditory canal. In these cases, at the House Ear Clinic we routinely recommend and perform a middle fossa approach. Continued refinements in this approach have led to superior hearing preservation results. Some patients also are candidates for a retrosigmoid approach. These are patients whom have small tumors that have only a small portion of the tumor located within the internal auditory canal. However, this is a minority of patients with acoustic neuromas who have only a small component in the internal auditory canal. In patients with small tumors who have been operated by the middle fossa approach at the House Ear Clinic since 1992, good hearing has been preserved in roughly two thirds of those patients. Any measurable level of hearing was preserved in eighty percent (80%) of those patients.
return to top of page »
SURGICAL APPROACHES
The choice of surgical approach depends upon the size of the tumor and the level of residual hearing detected on the audiogram. Again, the larger the tumor the lower the chances of saving hearing. The three most common surgical approaches for acoustic neuromas are the translabyrinthine, middle fossa and retrosigmoid approach. All of these procedures are performed under general anesthesia. Patients in general spend 5 days in the hospital, including the day of surgery.
Translabyrinthine Approach
This approach was refined and popularized by surgeons at the House Ear Clinic in Los Angeles. The House Ear Clinic group has the largest experience in the world with this surgical approach for acoustic neuromas and other skull base tumors. The translabyrinthine approach involves an incision that is made behind the ear. The mastoid bone and the balance canal structures of the inner ear are removed in order to expose the tumor. This approach results in complete tumor removal in nearly every case. One of the main advantages in this approach is that there is little or no retraction of the brain required to provide excellent exposure of the tumor. Another advantage is early and direct localization of the facial nerve which facilitates separation of the nerve from tumor, optimizing facial nerve outcome. After completion of tumor removal, the opening in the mastoid bone is closed with a fat graft which is taken from the abdomen.
This approach sacrifices the hearing and balance mechanism of the inner ear. As a consequence, the ear is made permanently deaf. Although the balance mechanism is removed on the operated ear, the balance mechanism in the opposite ear provides stabilization for the patient. Rarely patients experience transient vertigo immediately after surgery. This generally improves within the first five days following surgery and the patient has no further problems. In cases of larger tumors, the compensation for loss of the balance nerves on the tumor side has naturally occurred over time while the tumor has slowly grown to its large size. The patients rarely experience any vertigo in the early postoperative period.
Middle Fossa Approach
The middle fossa approach is another treatment that House Ear Clinic surgeons developed and currently utilize more than any other center in the world. This approach is used for small tumors and is utilized in cases when hearing is to be conserved. An incision is made beginning just in front of the ear and extends upward in a curved fashion. A small opening in the bone is made above the ear, and the membrane that covers the brain is elevated away from the bone and gently held away from the bony floor of the skull. Bone is then removed over the top of the internal auditory canal to expose the tumor. Tumor removal is complete in the vast majority of cases. Every effort is made to preserve hearing and still completely remove the tumor. In these cases of small tumors, hearing is preserved in the majority of cases in our experience at the House Ear Clinic.
Retrosigmoid Approach
An incision is made behind the ear and an opening in the skull is made behind the mastoid bone. The portion of the brain called the cerebellum is retracted away in order to expose the tumor. In most cases the tumor can be completely removed. Every effort is made in this approach to preserve hearing and still completely remove the acoustic neuroma. In some cases, because of invasion of the auditory nerve by the tumor, it is necessary to sacrifice hearing in order to completely remove the neuroma. The success of hearing preservation in these cases is largely dependent upon the size of the tumor and the condition of the auditory nerve in relation to the tumor.
return to top of page »
RADIATION THERAPY
Radiation therapy, in its various forms, has been applied to the treatment of acoustic neuromas. Historically this was done since the results of surgery in the past (prior to the 1970's) were actually quite dismal in most cases. However, with improvements in microsurgical technique and surgical approach, as well as, the acquisition of great experience by surgical teams such as at the House Ear Clinic, very few patients overall have undergone any form of radiation therapy for their acoustic neuroma. Since acoustic neuromas are benign growths we do not routinely advise radiation treatment. Radiation therapy is not risk free and does not result in disappearance of the tumor. Hearing loss, facial paralysis, and other serious complications have also occurred after radiation therapy. After this treatment, some patients have experienced continued tumor growth and have required surgical removal, which is much more difficult due to the effects of the radiation. High complication rates and especially treatment failures have been a particular characteristic of treatment with conventional and focused beam radiotherapy techniques. In recent years, patients have been treated with a different method of radiotherapy which is called stereotactic radiosurgery.
Stereotactic radiosurgery is a method of delivering a radiation dose in such a way as to minimize the affects of the radiation on the surrounding normal tissues while delivering a very high dose to the tumor. Low dose radiation beams are aimed from many different directions to converge on the tumor and, thereby, deliver a very high radiation dose. This type of treatment comes in several different forms. These methods are variously named the gamma-knife, LINAC, proton beam therapy, and fractionated radiosurgery. There are many questions that are not answered in terms of the long-term result of this therapy. These procedures are attractive to many patients because of the short-term promise of low complication rates and a shorter hospital stay. This form of treatment is an option only for patients with tumors measuring less than 3cm in diameter, as radiosurgery is ineffective in larger tumors.
A published series of patients treated by stereotactic radiosurgery have documented the various complications that can occur with this treatment. This includes facial paralysis, facial numbness, hearing loss, damage to the brain stem, hydrocephalus, and dizziness. Because of the high complication rates with early attempts at stereotactic radiosurgery, the various centers performing this treatment have continuously been decreasing the radiation dose delivered in these cases. This creates a very real concern for the long-term effectiveness of this therapy. It is well demonstrated that decreasing radiation doses leads to a lowering of the effectiveness of radiation treatments in both malignant and benign tumors. The question of long-term efficacy will not be answered for several more years when patients who have recently undergone this treatment are continually followed and studied for any recurrence of the tumor. These patients will need yearly MRI scans for many years to monitor the tumors for further growth. For the time being, this form of therapy has to remain classified as "experimental" because of the continuous alterations that are ongoing in radiation dose and the uncertain long-term effectiveness of the treatment.
Currently, most patients who are referred for stereotactic radiosurgery are elderly or are in poor general medical condition, making them a high surgical risk in terms of undergoing general anesthesia. The size of tumor is also extremely important in terms of someone's candidacy for this treatment. Tumors which are 3cm or larger in diameter are not candidates for stereotactic radiosurgery as it has been shown to be completely ineffective in these large tumors.
return to top of page »
THE House Ear Clinic PERSPECTIVE ON ACOUSTIC NEUROMA THERAPY
In the earlier part of the 20th century, many patients with vestibular schwannomas presented with debilitating neurological sequelae.(1) Olivecrona (1967) reported facial paresis at the time of tumor diagnosis in 54.7% of his patients.(2) This fact, combined with the emphasis placed on preservation of life, certainly explain Dandy’s (1941) statement. "Paralysis of the facial nerve must usually be accepted as a necessary sequel of the operation.".(3) Pennybacker and Cairns (1950), in their review of 130 cases of vestibular schwannoma, stated that "complete facial paralysis seems a small price to pay for relief from an acoustic tumour".(4)
Neural preservation in vestibular schwannoma surgery, like surgical mortality, has undergone tremendous evolution over the past century. With the introduction of the operating microscope and the revival of the middle cranial fossa and translabyrinthine approaches by William House in 1961, mortality rates dropped dramatically, and the focus of vestibular schwannoma removal shifted to the preservation of neural function. Patients undergoing vestibular schwannoma surgery today expect that they will survive surgery and are most concerned with preservation of facial function and, when appropriate, auditory function.
The total number of vestibular schwannomas removed at the House Ear Clinic now approaches 5000. With experience and refinements of technique, the results have progressively improved. Following is an up-to-date review of our past and present series with regard to postoperative outcomes.
Middle Cranial Fossa Approach
Hearing preservation is the major reason we use this approach in appropriately selected patients. Our hearing preservation rates described in five series from 1989 to the present demonstrate preservation of hearing to within 15 dB speech reception threshold (SRT) and 15% word recognition score (WRS) in between 59% and 71% of operated patients.(5-8) Our most recent published series demonstrated 60% Class A or B hearing according to the reporting guidelines of the American Academy of Otolaryngology-Head and Neck Surgery and we have seen the same success in the management of NF2.(5,9) These results compare favorably with those of recently reported gamma knife immediate post-treatment hearing preservation results.(10) We recently reviewed the duration of hearing preservation postoperatively and found 89% of patients retained useful hearing with a minimum of 5 years of postoperative follow-up. This is in sharp contrast to the radiation therapy literature demonstrating significant hearing deterioration over time.
The middle cranial fossa approach has, in the past, been described as an approach placing the facial nerve at undo risk. This has not been our experience. Our most recent reviews demonstrate excellent postoperative facial nerve function (House-Brackmann Grade I or II) in over 94% of our patients.(7,8)
The middle cranial fossa approach provides an unobstructed view of the entire IAC and its contents. This allows complete tumor removal under direct vision. In a review of 500 cases with several years of follow-up, we identified only one case of residual tumor (0.2%).
We have not seen a permanent neurological complication following this approach. A single patient experienced a postoperative seizure that responded to Dilantin. After one year of seizure prophylaxis the Dilantin was stopped and no further seizures have occurred. We feel our low rates of complications are the result of short temporal lobe retraction times (average 90 minutes).
Translabyrinthine Approach A recent review from our database of vestibular schwannoma cases provides data from 1302 patients who underwent a translabyrinthine approach between 1982 and 1993. Their mean age was 50.0 years, and 46 per cent were male and 54 per cent were female. Tumor size varied from 0.5 to 6.5cm, with a mean size of 2.4cm. Operating time averaged 3.3 hours. Three (0.2 per cent) deaths occurred in this series.
Data on long-term (6 months) facial nerve function as determined by the House-Brackmann scale were available on 889 cases, with a mean follow-up time of 2.1 years. Of these, 58.2 per cent had a grade I function; 12.6 per cent, grade II; 13.2 per cent, grade III; 7.8 per cent, grade IV; 3.3 per cent, grade V; and 5.1 per cent, grade VI. In this same group of patients undergoing surgery since the advent of facial nerve monitoring (1988), 59% were grade I, 15.4% were grade II, 9.3% were grade III, 7.7% were grade IV, 4.2%, were grade V and 4.5%, grade VI. The vast majority of the poor facial nerve outcomes occurred in larger (greater than 4 cm) tumors. When comparing the risk of facial nerve paralysis in comparable tumors (<3.0 cm), the surgical risks in our hands are only a few percent greater when compared to the most recent gamma knife reports cited above.
Postoperative Follow-Up
In our experience, vestibular schwannomas rarely recur after translabyrinthine removal. Our recurrence rate for unilateral tumors removed through the translabyrinthine approach treated between 1961 and 1995 was 0.3%.(11) The average interval to recurrence was ten years. Based upon these findings we have recommended a single gadolinium-enhanced MRI five years postoperatively.
return to top of page »
Stereotactic Irradiation
Radiosurgery is a term originally popularized by Leksell referring to a procedure that delivers three-dimensional stereotactic external-beam irradiation to a specified tissue volume in a single session. This term is now applied to various techniques, including gamma-units using 60Co photons, protons, helium ions, and neutron beams and modified linear accelerator units (linac). Stereotactic external-beam irradiation differs from conventional external-beam radiation therapy in several important ways: 1) Treatment of small tissue volumes in the range of 1 to 30 cm3, 2) A single fraction of radiation is typically delivered. Some institutions are exploring fractionated therapy, but, for the treatment of vestibular schwannomas, long-term data with significant numbers of patients is lacking, and 3) High-dose gradients at field edges minimize dose deposition outside the target volume. Since its introduction in 1969, the gamma unit has been used to treat vestibular schwannomas based upon these principles. Initially utilizing high marginal doses and CT planning, the complications reported from experienced centers far exceeded those reported from microsurgical centers of excellence (12). With the improved technology of MR imaging for treatment planning, and the gradual empirical reduction in marginal dosing, the complication rates have reached levels comparable to those reported by microsurgical centers of excellence.
As discussed previously, the evolution of goals in the treatment of vestibular schwannomas has shifted from solely the preservation of life, to include the preservation of function (facial and auditory). What must be common to any form of intervention, should one be chosen, is the goal of life-long control.
The concern over the management of these benign tumors with stereotactic irradiation lies partially in this principle of life-long control. Studies have clearly demonstrated a dose response relationship with single fraction radiation. This relationship, at the current doses employed to the tumor margin, does not demonstrate complete cell kill. This fact is based upon the fundamentals of radiation induced cell death. Irradiated cells are most sensitive to injury during metaphase. Benign tumors have few cells in this phase of the cell cycle in comparison to malignant tumors. The ultimate result of irradiation is DNA damage secondary to the direct effects of the gamma rays, or strand breaks from oxygen radicals that are generated. There are also indirect tumor effects that result from radiation induced damage to nutrient vessels. The cells with damaged DNA either undergo apoptosis (programmed cell death) due to the load of DNA strand breaks, or, they undergo cell cycle arrest. The total and marginal doses currently prescribed have been done so empirically, with insufficient biological evidence that the cells will all undergo apoptosis. These cells will not remain in cell cycle arrest indefinitely. They will either enter an apoptotic pathway, or they will harbor radiation/repair-induced mutations that will allow them to re-enter the cell cycle and grow.
The time that it will take to see the fraction of tumors with cells re-entering the cell cycle can only be estimated as there is no long-term (20 to 30 years) follow-up. All of the irradiated vestibular schwannomas seen at our institution, and in the literature, demonstrate enhancement up to a decade after treatment suggesting a significant fraction of cells that have not undergone apoptosis.
As dosing has recently undergone significant reduction in an effort to reduce complications, a brief review of current data from experienced centers is provided. Flinkinger et al. recently provided data on one hundred ninety nine patients receiving gamma knife radiotherapy (median marginal dose of 13Gy) for their vestibular schwannomas with a median follow-up of 30 months.(13) The range of follow-up with the number of patients at each year was not provided. Additionally, the authors state that they had "more than one year MR follow-up" in 147 patients. Of those followed, to their knowledge, five patients (3.4%) have required microsurgical removal for continued tumor enlargement. In this same group of patients they identified MR evidence of 1 to 2 mm of tumor growth in nearly 10%.
In a recent series of patients treated with the gamma knife (marginal doses of approximately 13 Gy), Prasad et al. reviewed 95 patients with between 5 and 10 years of follow-up and found tumor growth in 6.3%.(14) When analyzing their complications, they noted that despite hearing preservation in many of the patients immediately after treatment, approximately 60% lost their preserved hearing over time. These figures support those of the Marsailles experience outlined in the preceding chapter. We also agree with the Marsailles group that cystic tumors should be considered for microsurgery due to the risk of post-irradiation complications.
We believe that all of these series lack sufficient follow-up. This is best illustrated by the experience with radiotherapy in another benign intracranial neoplasm, pituitary adenomas. In a study of radiotherapy for nonfunctional pituitary adenomas, Breen and co-authors demonstrated actuarial tumor control rates of 77.6±6.3% and 64.7±12.9% at 20 and 30 years, respectively (15). From these studies it is clear that to completely assess tumor "control" with radiotherapy it will require several decades of follow-up on these newer dosing strategies. As mentioned above, these irradiated tumor cells may re-enter the cell cycle due to induced mutations, potentially in genes regulating growth control resulting in neoplasia. Several authors, in contrast to the findings of Breen et al., state that radiation failures will occur early. This has not been our experience in the thirty cases of microsurgical management of radiation failures performed at our institution. We have seen several cases of failure beyond three to five years.
As described above radiation induced mutations can occur in other growth control genes leading to neoplasia. Studies in primates exposed to single dose radiation, similar to those given with gamma knife for vestibular schwannomas, demonstrated a 50% incidence of malignant brain tumor in the decade following irradiation.(16) In study of neoplasia in patients receiving radiation therapy for adeno-tonsillar hyperplasia, approximately one-third developed thyroid gland tumors and many were malignant.(17) In this same cohort of patients there were 66 neural tumors (2.2%), 67 salivary tumors (2.3%) and 93 carcinomas (3.1%) of multiple tissue types. In a follow-up study of 3013 of this same cohort receiving 7.5 Gy in three divided doses over three weeks, 85 neural tumors were identified in 70 patients (2.3%).(18) This included fifteen meningiomas, twenty-seven cranial nerve schwannomas and one malignant neural sheath tumor. The incidence of vestibular schwannoma in this group of patients was 0.7%, nearly 1000-fold greater than the normal population. One of the most striking features of this study was that new tumors were being identified more than 30 years after the initial treatment. This underscores the need for long-term follow-up not only for re-growth of the treated vestibular schwannoma, but, the appearance of radiation induced neoplasia. To date, there have been several reports in the literature of malignant tumors appearing after radiation therapy for vestibular schwannomas(19-22). Based upon the findings of Breen described earlier for radiated pituitary adenomas an actuarial rate for developing a radiation-induced neoplasm of 2.7±1.9% at 10 and 30 years, and the data sited above, we will likely be seeing similar results after vestibular schwannoma radiation therapy.
Conclusions
Based upon our current rates of hearing preservation, facial nerve functional preservation and cure (over 99%), we recommend microsurgery for those patients undergoing therapy for their vestibular schwannomas. We strongly recommend against radiation therapy for NF2 based upon our results and the unknown effects of irradiation in a condition known to result from a mutation in a growth control gene(19).
As no mode of therapy is without risk, we thoroughly discuss tumor observation with patients that have this as an option. Until studies demonstrating long-term tumor control (a minimum of three decades) with less than the expected rate of malignant transformation (approximately 3%) are available, we will only recommend radiation therapy for patients requiring treatment that are not surgical candidates either by personal choice or infirmity. Often, these are older patients.
return to top of page »
|
FIGURE 1. Preoperative MRI scan showing the 2 cm acoustic neuroma in the left internal auditory canal. |
|
FIGURE 2. Postoperative MRI scan demonstrating total resection of the acoustic neuroma on the left. The whitish material on the left is a fat graft placed in the area of the surgery to seal off the space containing cerebrospinal fluid. |
|
|
FIGURE 3. Preoperative MRI scan showing a 3.5 cm acoustic neuroma exerting pressure on the brain stem and cerebellum |
|
| FIGURE 4. Postoperative MRI demonstrating an approximately 90% reduction in the size of the tumor. The patient had no neurological deficits as a consequence of surgery, made a full recovery and actually improved neurologically with the pressure off the brain stem and cerebellum. |
|
House Ear Clinic ACOUSTIC NEUROMA PATIENT CASE STUDIES
Case 1 (CS1, CS2)
This 57 year-old woman presented with a several month history of tinnitus (ringing in the ears) in her left ear. Her doctor sent her to an Ear, Nose, and Throat (ENT) specialist who ordered an MRI scan of her brain. A 2 cm mass was detected in the left internal auditory canal. (Figure 1) She was then referred for consultation to one of the HEC physicians who ordered an audiogram. Her hearing was intact at a near normal level on the audiogram in the left ear. After consultation it was decided that the best treatment in her case was total surgical removal of the tumor via a middle fossa approach to try and save her hearing.
Her tumor was totally removed. (Figure 2) The facial nerve function was perfect after surgery. Hearing was preserved within 10% of her preoperative level on audiogram. She spent 5 days in the hospital (including the day of surgery) and was back to work after a one month recovery period at her home. She has no residual problems after surgery and her tinnitus resolved by 3 months.
Case 2 (CS3, CS4)
A 72 year-old man with Parkinson's disease had been followed for several years by his neurologist and treated with medications. He became increasingly unsteady and could no longer walk without the assistance of a walker. This deterioration prompted his neurologist to obtain an MRI scan of the brain. This demonstrated a very large tumor on the right side consistent with an acoustic neuroma. (Figure 3) An audiogram was performed which showed the patient had completely lost hearing in the right ear. The patient's age and symptoms dictated that a reduction in tumor size to relieve pressure from the brainstem was the goal of treatment. The most effective way to accomplish this is surgical debulking of the tumor.
The patient underwent a retrosigmoid approach for debulking of the tumor. (Figure 4) The surgery was performed in less than 4 hours and the patient spent one night in intensive care. After surgery facial nerve function was perfect and he had no new problems. He made an uneventful recovery, spending 6 days in the hospital and returned home. His unsteadiness improved and he was able to walk without the walker by 2 months following surgery.
Case 3 (CS5, CS6)
A 26 year-old woman first noticed hearing loss and balance problems 4 years prior to her referral to the House Ear Clinic. She was seen by a neurosurgeon in her city 2 years earlier and was diagnosed with a right-sided 2 centimeter diameter acoustic neuroma. She was told not to worry about this since "these tumors grow slowly". She continued to gradually lose her hearing and then began having difficulty swallowing. A CT scan of the brain and MRI were then performed showing the tumor had indeed grown significantly over 2 years. It was now 6 centimeters in diameter. (Figure 5)
The patient and her husband researched their options and were directed to the House Ear Clinic in Los Angeles, opting for the most experienced center in the world. She underwent a translabyrinthine approach for a total resection of the tumor. (Figure 6) Her facial nerve was preserved anatomically and had some function after surgery. Facial nerve function has subsequently improved. Her unsteadiness resolved as did her swallowing difficulties in the months following surgery.
|
| FIGURE 5. Preoperative scans showing the very large acoustic neuroma. This set demonstrates the different views obtained by plain CT, CT with contrast and MRI with contrast. |
|
| FIGURE 6. Postoperative CT scan with contrast demonstrating total tumor removal. |
|
|
| FIGURE 7. Post gamma knife MRI scan showing the growing tumor 2 years after stereotatic radio surgery. |
|
| FIGURE 8. Histologic section of the acoustic tumor removed by House Ear Clinic surgeons which contains many active tumor cells. These are present despite previous treatment with gamma knife radiosurgery. |
|
Case 4 (CS7, CS8)
A 59 year-old man experienced gradual hearing loss and was diagnosed with a 2 centimeter acoustic neuroma. He underwent surgery via a retrosigmoid approach at another institution. His hearing was lost completely and he had some weakness of his facial nerve. Eighteen months later he had a follow-up MRI which showed that the tumor had returned, again approximately 2 centimeters in size. This time he opted for treatment with the gamma knife. He received a dose of 26 centiGray and had no side effects from radiation.
FUTURE DIRECTIONS IN THERAPY
Physicians and scientists at the House Ear Clinic and House Ear Institute in Los Angeles are at the forefront of cutting edge research in hearing science and the biology of acoustic neuromas. Research is also ongoing in novel treatment strategies for other tumors that affect the base of the skull. Patients are involved in clinical trials of neuro-protective agents which are being studied for their effectiveness at improving hearing preservation, as well as, facial nerve function after surgery for acoustic neuromas.
Scientists at the House Ear Clinic and Institute are studying schwannoma cells (the tumor sells in acoustic neuromas) in an effort to develop gene therapy protocols. This genetic approach will likely take many years to develop, but certainly has promise.
Two years later he had a routine follow-up MRI scan, which unfortunately detected a tumor that measured 2.5 centimeters in size. (Figure 7) The tumor was growing, despite the gamma knife treatment with a very high dose of radiation. (Figure 8) He then sought the help of physicians at the House Ear Clinic.
A translabyrinthine approach was performed and the tumor was completely removed. Unfortunately, gamma knife treatment had resulted in scar tissue formation around the tumor and the facial nerve. This made it impossible to save his facial nerve and he was left with an immediate total facial paralysis. Several days following his surgery he underwent facial reanimation surgery. His surgeon connected the nerve that moves the tongue to the facial nerve, called a facial-hypoglossal anastomosis. He has since recovered some of his facial function, but still has some weakness.
return to top of page »
References
1. Cross JP. Unilateral neurilemmomas of the eighth cranial nerve: Then and now. Am J Otol. 1981:3;28-34.
2. Olivecrona H. Acoustic tumors. J Neurosurg. 1967:26;6-13.
3. Dandy WE. Results of removal of acoustic tumors by the unilateral approach. Arch Surg. 1941:42;1026-1033.
4. Pennybacker JB, Cairns H. Results in 130 cases of acoustic neurinoma. Journal of Neurology, Neurosurgery, and Psychiatry. 1950:13;272-277.
5. Brackmann DE, Owens RA, Friedman RA, Hitselberger WE, De la Cruz A, House JW, Nelson RA, Luxford WM, Slattery WH 3rd, Fayad JN. Prognostic factors for hearing preservation in vestibular schwannoma surgery. Am J Otol 2000; 21:417-424.
6. Shelton C, Brackmann DE, House WF, Hitselberger WE. Middle fossa acoustic tumor surgery: Results in 106 cases. Laryngoscope 1989; 99:405-408.
7. Brackmann DE, House JR 3rd, Hitselberger WE. Technical modifications to the middle fossa craniotomy approach in removal of acoustic neuromas. Am J Otol 1994; 15:614-619.
8. Slattery WH 3rd, Brackmann DE, Hitselberger W. Middle fossa approach for hearing preservation with acoustic neuromas. Am J Otol 1997; 18:596-601.
9. Brackmann DE, Fayad JN, Slattery WH, Friedman RA, Day JD, Hitselberger WE, Owens RM. Early proactive management of vestibular schwannoma in neurofibromatosis type 2. Neurosurg. 2001:49;274-283.
10. Niranjan A, Lunsford D, Flickinger JC, Maitz A, Kondziolka D. Dose reduction improves hearing preservation rates after intracanalicular acoustic tumor radiosurgery. Neurosurg. 1999:45;753-765.
11. Shelton C. Unilateral acoustic tumors: how often do they recur after translabyrinthine removal? Laryngoscope. 1995:105;958-66.
12. Noren G, Greitz D, Hirsch A, Lax I. Gamma knife surgery in acoustic tumors. Acta Neurochir Supp 1993:58;104-107.
13. Flickinger JC, Kondziolka D, Niranjan A, Lunsford D. Results of acoustic neuroma radiosurgery: an analysis of 5 years’ experience using current methods. J Neurosurg. 2001:94;1-6.
14. Prasad D, Steiner M, Steiner L. Gamma surgery for vestibular schwannoma. J Neurosurg. 2000:92;745-759.
15. Breen P, Flickinger JC, Kondziolka D, Martinez AJ. Radiotherapy for nonfunctional pituitary adenoma: analysis of long-term tumor control. J Neurosurg. 1998:89;933-938.
16. Beir V. Health effects of exposure to low levels of ionizing radiation. National Academy Press, Washington D.C.
17. Schneider AB, Shore-Freedman E, Ryo UY, Bekerman C, Favus M, Pinsky S. Radiation-induced tumors of the head and neck following childhood irradiation. Medicine. 1985:64;1-15.
18. Sznajder L, Abrahams C, Parry DM, Gierlowski TC, Shore-Freedman E, Schneider AB. Multiple schwannomas and meningiomas associated with irradiation in childhood. Arch Intern Med. 1996:156;1873-1878.
19. Baser M, MacCollin M, Sujansky E, Evans DGR, Rebenstein A. Malignant nervous system tumors in patients with neurofibromatosis type 2. Presented at the 1996 FASEB Summer Research Conference on Neurofibromatosis, Snowmass, CO, June 29, 1996.
20. Wiet, R.J., Micco, A.G., Bauer, G.P. Complications of the Gamma Knife. Arch Otolaryngol Head Neck Surg, 1996. 122: p. 414-6.
21. Fagan, P., Chang, P., Turner, J.Triton Tumour - Letter to the Editor. Journal of Neurosurgery, 1999. 90: p. 987-989.
22. Shamisa A, Bance M, Nag S, Tator C, Wong S, Noren G, Guha A. Glioblastoma multiforme occurring in a patient treated with gamma knife surgery. J Neurosurg. 2001:94;816-821.
|
