Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Acoustic Neuroma – Blade vs. Photon The formation of an acoustic is the over proliferation of Schwann’s cells, usually beginning along the vestibular nerve in the internal auditory canal at the junction at the peripheral and the central myelin. Therefore, an acoustic neuroma is more accurately described as a vestibular neuroma if the nomenclature were based on the nerve of origin. It is generally a slow growing, benign tumor; however, the exact growth rates are variable and while the explicit mechanism determining growth rate has not been elucidated, it has been noted that growth rate is dependent on the fraction of tumor cells in the proliferative phase of the cell cycle. The more cells in the proliferative phase, the faster it will grow. Tumors are generally described as slow or medium growing and these are the majority of patients. Fast growing tumors are defined as those tumors growing at about 1cm per year in diameter. Tumors are roughly spherical in nature and therefore their volume depends on the equation for volume of a sphere, which is proportional to the radius cubed. Therefore, even small changes in the diameter relate to large changes in volume. Acoustic tumors or neuromas usually rise up from the nerve trunk of the vestibular nerve and gradually grows out of it as it increases in size and assumes a peripheral position. The vestibular nerve measures about two inches from the site of origin of the brain stem to its termination point in the labyrinth. It has two portions, the inferior division and the superior division. These tumors appear to occur with equal frequency in each of these divisions. More specifically, neuromas are believed to originate at the transition zone from the central to peripheral myelin, which is known as the Oppersteiner-Redlick zone, which occurs nearly halfway along the length of the vestibular nerve. This area approximates the vestibular ganglion known as the Scarpa’s ganglion, which is believed to be the specific site of origin. On this slide I have a better picture that shows the proximity of the 6 th, 7 th, and 8 th and all the cranial nerves. So here is the 6 th nerve, 7 th, 8 th, here is the vagus nerve, and here is the spinal accessory nerve. By mass effect acoustic neuromas can affect any of these nerves. A schwannoma begins as a confined lump of growth that compresses the adjacent axons around its periphery as it expands within the perineurium. This is different than a neurofibroma, which is shown in the bottom here, which forms from axons causing obstruction and thinning of the Schwann’s cells and a reactive perineurium. Here is acoustic neuroma compressing these axons here and here is a neurofibroma as seen in neurofibromatosis. A typical microscopic appearance of acoustic neuromas has two distinct cellular characteristics, which are termed Antoni-A and Antoni-B fibers. Antoni-A are represented by these cells here and Antoni-B are by these loosely packed cells here, and as shown in this micrograft, it can occur either independently or together and their presence has no known clinical correlation. As a tumor grows, it typically follows the path of least resistance, which is immediately into the cerebellar pontine angle. On rare occasions, tumors grow laterally into the vestibule of the inner ear area and even into the middle ear cavity. Thus most tumors consist of two portions, a stalk within the internal auditory canal and the main extra temporal portion of the cerebellar pontine angle. Here is a small acoustic neuroma growing and as it gets bigger it starts to fill up the cerebellar pontine angle, then it starts to compress the brain stem and this picture shows further compression and this would give you resulting hydrocephalus. There are two distinct clinical presentations: bilateral and unilateral. Bilateral tumors occur in patients with neurofibromatosis type II and the unilateral occur in the sporadic form. They are both associated with neurofibromatosis type II gene which is believed to be a tumor suppressor gene. An acoustic neuroma accounts for 6% of all intracranial tumors, but 80% of all tumors found at the cerebellar pontine angle are acoustic neuromas. The yearly instances are about 1:100,000. It is believed that there are total of less than 1000 persons in the United States with neurofibromatosis type II. The incidence, however, in cadavers of the acoustic neuromas has been found to be about 2.4%. So there is a large discrepancy between the detected and actual incidence. Acoustic neuromas are commonly associated with hearing loss but can manifest in other ways. Their symptomatic presentation is affected by their site of origin as well as their growth pattern. The internal auditory canal houses the cochlear vestibular nerves, facial nerves and internal auditory artery, and as it grows it compresses these structures and collapses into the cerebellar pontine angle as I described. If the tumor grows superiorly it can impinge on the trigeminal nerve and abducens nerve, and if it grows inferiorly it can compress the glossopharyngeal nerve, the vagus nerve, and the spinal accessory nerves. Continued growth causes pressure to the cerebellum, compression of the fourth ventricle causing hydrocephalus. It is the hydrocephalus that causes headaches and visual loss in progressive neurological deterioration and eventually death. In fact, in the 19 th century it was understood that a patient with unilateral hearing loss, facial numbness together with headache and progressive bilateral visual loss had a lesion of the cerebellar pontine angle. In 1992, Celznik, Jackler, and Pritzly at UCSF published a paper reviewing their records of 136 patients newly diagnosed with an acoustic neuroma, and reports the average symptom durations of tinnitus and hearing loss both occurred almost four years prior to diagnosis followed by vertigo at 3.6 years, and then after a long hiatus, headache was noted, disequilibrium, and lastly trigeminal symptoms occurring about just under one year prior to diagnosis. The facial nerve symptoms were about 0.6 years before diagnosis. These durations are not much different today even with the use of MRI. Both the growth and symptom evolution are obviously continuous events the growth of acoustic neuromas can divide into a series of three stages, intracanalicular stage, the cisternal stage and brain-stem concussion stage. In the intracanalicular stage is associated with hearing loss, tinnitus and vertigo. This hearing loss is typically high frequency sensorineural hearing loss that is usually unilateral or asymmetric and there is an impairment of the speech discrimination score out of proportion to the patient’s pure tone deficits. About 85 % of all patients will complain of hearing loss. A quarter of the time it is sudden in onset and while only 15% of patients will complain of hearing loss, if you get an audiogram only 4% of them will actually have a normal audiogram. This hearing loss however, does not appear to be related to the size of the tumor. The cisternal stage is associated with worsening of the auditory symptoms, transition from the vertigo to the disequilibrium and occasionally headaches. The brain stem compression causes all of the previous symptoms to be worse. In addition, hydrocephalus can cause the headache and visual changes such as visual loss and double vision. Before talking about the different modalities of treatment for acoustic neuromas, it is important to first look at their natural course without treatment. Since 1985 there have been many reports in the literature investigating the role of conservative management in acoustic neuromas. There are at least 26 studies reviewing over 846 patients with acoustic neuromas followed for a mean time of approximately 3½ years. There is a female preponderance of 1.5:1 and the average age of 63. The number of patients per study ranged from 4 – 123 patients, and only 8 of these studies included patients with neurofibromatosis type II. Let’s first look at the percent of acoustic neuroma which grew; 52% of the acoustics grew, there was no growth in 43% of the patients, and there was involution in 5% of the patients. The mean annual growth rate was about 1.4 mm per year. However, the range of individual tumor growth rates varies widely and is highly variable in anywhere from involuting at –4.8 mm per year to growing rapidly at 30mm per year. Most acoustic neuromas grow slowly; about 80% grow less than 2 mm per year, and as noted above, there is that large discrepancy in the tumor growth rate between individuals and this has lead some authors to categorize the tumors into substance based on their rate of growth. However, this has not really added any prognostic value. In a recent study by Dr. O’Reilly and colleagues, he looked at 44 consecutive patients. He followed these patients with gandolium-enhanced MRI for an average time of about 2½ years. About half of the lesions were within the internal auditory canal and half were in the cerebellar pontine angle and 70% of the tumors he reviewed displayed no growth. Now what is interesting is that of the 12 tumors that did grow, nearly half were intercanalicular and half of them were not. So, you could not say that one tumor in one location had more predilection to grow than the other. Most authors now agree that the growth of an acoustic neuroma is unpredictable. There seems to be no correlation between the patient’s age nor the initial tumor diameter and future tumor growth and there can be rapid growths several years after a period of no growth, although this appears to be more the exception rather than the rule. The possible reasons for the rapid growth include rapid metallic activity, cyst formation, hemorrhage and/or edema. In addition, a number of immunohisto-chemical DNA flow studies and chromosomal studies have failed to show any reliable predictors of growth of acoustic neuromas. What seems to hold true is that tumors which will ultimately require intervention seem to grow more rapidly. The mean annual growth rate of tumors that failed conservative therapy was 4.8 mm per year. But again this is very variable. In addition, the study by Walsh showed that a markedly different growth rate for these tumors which were intercanalicular at the time of diagnosis and a had a growth rate of only 0.2 mm per year, while those that extending into the cerebellar pontine angle grew about seven times faster, about 1.4 mm per year. In this large study that we reviewed of the 846 patients, about one-fifth of all patients watched conservatively failed conservative therapy and required some sort of intervention. Now this only represents a three year followup time, so you have to look at the data carefully. But we can conclude, I think, that if conservative management is chosen then followup must be for life and be close. In reviewing the literature, it is difficult to assess the impact of conservative management on hearing loss because different authors use different definitions of hearing preservation. Some only look at the pure tone average while others look at the speech discrimination scores, and reports are widely variable. There is a study done by Charvey in 1995 in the otolaryngology and surgery journal. He reported that 23 patients lost their eligibility for hearing preservation operation either because of deteriorating hearing or tumor growth. Over 70% of these patients had small tumors less than 15 mm in diameter. Most of the patients had small tumors. Then in contrast, Yamamoto et al in 1998 in the Minimally Invasive Surgery Journal reported that neither tumor growth nor deterioration of auditory acuity occurred in 5 of 12 patients. In a study by Walsh, looking at 72 patients, he has found that deterioration of audiological function had nothing to do with the tumor size at all. And so, we can see from these three studies I presented, which are fairly representative of the literature, the effect of tumor size and hearing seems to be unclear. The recommended criteria for conservative management is the patient with poor general health, the patient with small tumor size, especially if it is intracanalicular, if they have minimum or no symptomology, if the tumor is in the only or the better-hearing ear, and if the patient has neurofibromatosis and any combination of the above four criteria. Obviously, conservative management is not the treatment of choice in many patients. There are two main classes of treatment now available for acoustic neuromas, surgical excision and radiotherapy. Radiotherapy includes gamma knife, Lynac, or linear accelerators using x-rays, and a conventional fractionated therapy using a variety of radiation resources. Historically, surgical excision has been the goal standard by which all acoustic neuromas have been treated. However, in the late 1960’s radiotherapy for the treatment of acoustic neuromas began and the field is rapidly evolving. I think we should first begin with surgical therapy as it has been around for the longest period of time and is the standard by which any alternative therapy must compare. As you are all aware, there is an enormous amount of data concerning the results and outcomes of surgical therapy so we will only be reviewing representative data from some large published studies. Looking at the history of surgical therapy, acoustic neuromas were an early target of neurosurgeons because at the time the only intracranial tumors which could be reliably localized were those that involved either the motor strip or the cranial nerves at the base of the brain, and because they could be localized by their symptomology. Acoustic neuromas with their characteristic presentation were easy to diagnose and to localize. The earliest attempt at removal of acoustic neuromas was performed by Charles McBurney of New York in 1891, who has been immortalized by the appendectomy incision, which bears his name. They reported that after opening the suboccipital plate with a mallet and gouge, the cerebellum swelled massively, so much so that it had to become necessary to “shave off the excess”, this was due to the marked hydrocephalus those patients presented with at that time. No tumor was removed, and the patient, not surprisingly, died twelve days later. The first successful results were achieved in 1894 by Dr. Valance in London and Dr. Enindale in Scotland. In these very early attempts, a unilateral suboccipital craniotomy was employed. A complete removal was performed by finger dissection, hemostasis was obtained by packing the cerebellar pontine angle with gauze and there was a grave emphasis upon operative speed; however, the outcome was dismal. The initial mortality was echoed by many of those who were to follow. The few successes reported left patients severely crippled. The next area in acoustic neuroma surgery was pioneered by Dr. Harvey Cushing of John Hopkins and then later Harvard. In 1905, he advocated only decompression of the posterior fossa by extensive removal of the suboccipital bone, fearful that actual resection of the tumor would not be safe. Dr. Cushing then developed a bilateral suboccipital craniotomy. However, he did not advocate complete excision of the tumor only removal of the core thereby, protecting the brain stem vasculature and often preserving cranial function. His mortality rate was only 20% in 1970 and decreased with some refinements in his technique to only 4% in 1931. While the mortality of the procedure was low many patients might have to succumb to their residual tumor because he left some of it in there. Dr. Walter Dandy who was a pupil of Dr. Cushing, and also trained at John Hopkins, felt that complete excision was necessary and first reported complete excision in 1960. By 1941, he described a unilateral suboccipital approach where he gutted the tumor and then gently drew the capsule away from the brain stem, with resulting mortality of about 10%. The next advance in acoustic neuroma surgery was the development of the translabyrinthine approach, which while not first performed by Dr. William House, was indeed perfected by him in the early 1960s with more detailed view offered by the operating microscope and control of an operating drill. Of interest is that the approach was criticized by both Dr. Cushing, an otologist, who would never think of such a preposterous approach, and Dr. Dandy, who also felt that the approach was much too dangerous. Dr. Albercrono Stockholm during the late 1930s and 1940s was the first to place great emphasis on facial nerve preservation, which is so routine to us today. He also employed a type of facial nerve monitor applying electrical stimulation to identify the nerve and he had a special nurse observe the face during the procedure. And finally Dr. Poole and Dr. Pava of New York in 1957 were the first to advocate the removal of the intracanalicular component of the tumor because up until this point, surgeons would truncate the tumor at the porous acousticus and coagulate the remnant. Now to compare radiosurgery versus micro surgery, I have elected to concentrate on six different categories to determine treatment success. These include tumor growth, facial nerve function, hearing preservation, need for further treatment, mortality and treatment specific complications such as CSF leak or meningitis in surgery or hydrocephalus in radiation therapy. In a review published in 1997 by Dr. Sammy Emattes in Hanover, Germany at the Norsdadt Hospital of 1000 vestibular schwannomas, which they operated on, they reported a 98% complete excision rate with less than 1% recurrence rate, 7 out of 880 cases. Now in looking at the facial nerve function, others have adopted a grading system developed in 1985 by Dr. House and Dr. Brackmann as shown here. You can review the slide but the one important thing I want to point out is grade 4 with the House/Brackmann grading system, you get incomplete eye closure and they have obvious facial weakness that is disfiguring to the patient, so I think any surgical result, any grade 3 or better would be considered a good result as they can close their eye and do not have complications from dry eye. It is well published that the tumor size greatly effects patient nerve function postoperatively. In multiple studies by various authors it has been repeatedly reported that an intracanalicular tumor can be completely resected leaving the facial nerve function completely intact 100% of the time. So far intracanalicular tumor surgery is 100% successful. Looking at some samples of studies from the literature of experienced microsurgeons, we can see the results of facial nerve functions for various size of tumors and level of functions of the nerve after surgery. It is kind of a complicated slide, but basically there are three numbers in this column, the results are graded by size of the tumor; small is less than 2 cm, medium is 2 to 3.9 cm, and large is greater than 4 cm. There are four studies here and there are many cases. He did not categorize the grade of the patient or function, he only said whether it was working or not. This first number represents the percent of patients having a grade 1 or grade 2 facial nerve function, the second number represents House/Brackmann grade 3 or 4 and the last number represents House/Brackmann grade 5 or 6. And basically you can see that the trend from small and large, this number gets smaller in every case. Basically for small to medium tumors the results are pretty good. If you look at grade 4 and above you are looking at 90%-100% success in preserving facial nerve function. In a study published by Dr. Sammy Emattes reviewing 1000 vestibular schwannoma resections, 979 which were total resections and 21 cases were purposely subtotal resections for decompression only, the authors reported an overall anatomic preservation of the facial nerve in 93% of the cases. The ranges of preservation range from 86% if the tumor is greater than 30 mm to 94% for tumors which were less than 3 cm. In the case of cystic masses, the preservation rate was a little bit lower at 88%. Now the results of their facial nerve function, not anatomic nerve preservation, but function, were as follows: So here we have the preop incidence of facial paresis of some sort, 17% of the patients had some facial paresis and postoperatively, that jumps to 53%. Of these 17%, these are represented by these numbers right here so 8.6, 0.71 and 1.3 add up to 17% and you can see that there is a drop of 83% of patients that came in with a grade 1 level function, it dropped down to 47% after surgery. These other ones are not too bad. Overall they had 73% of their cases had a House/Brackmann grade 3 or better result. Dr. Wigen and Fickel reviewed the acoustic neuroma registry in a recent paper looked at all the cases in the acoustic neuroma registry from 1989 to 1994 and looked at 1,579 patients. There were 87 patients who had preoperative facial nerve palsies, 50% of the patients had normal postoperative function, 44% had worse postoperative function, and 2% had improved postoperative facial nerve function. They also broke down the tumors by their size and by the surgical approach. And if you look at intracanalicular tumors using the translabyrinthine approach, there are no reported cases of any facial weakness. For intracanalicular tumors from a posterior fossa approach, the grade 1 or 2 was 90% of the time; patients had a House/Brackmann grade 1 or 2 of facial nerve function. If you look at the rest of the results, again, the trend is the larger the tumor, the lower the facial nerve function. When hearing preservation is a consideration, only the middle fossa or suboccipital approaches can be used. There is an intrinsic difficulty in interpreting data on hearing preservation because various series have used different criteria to define serviceable hearing. One popular classification is this one here where serviceable hearing is any hearing that has a speech reception threshold of less than 50 decibels and a speech discrimination score greater than 50%. The American Academy of Otolaryngology and Head and Neck Surgery, classification is listed here and some authors will referred to that in their literature, but some authors just do whatever they want to get the numbers they want. I reviewed literature by Dr. Secar and Dr. Gourmley of the George Washington University in 1996 found that hearing preservation rates vary depending on tumor size just as with patient facial nerve functions. Most microsurgeons have classified acoustic neuroma size as follows when showed earlier, small is less than 2cm medium 2cm to 3.9cm, and large greater than 4cm. Based on this classification, they found the ranges of hearing preservation as follows here on this slide. There is a wide range depending on the skill level of the surgeon and other factors but small tumors 45%-82%, medium 22%-50%, and large tumors anywhere from no hearing at all to 33% of some hearing preservation. There was a study done by Dr. Brackmann at the House Ear Institute in Los Angeles, California, which has published this past year reviewing of 333 patient. Now, preoperatively 90% of these patients had serviceable hearing, which is the criteria listed there. The way you look at this slide is, this is the preoperative hearing 60% had class A hearing by the AAO guidelines and 30% had class B hearing. Postoperatively you read this direction, 33% of patients went from 60% preoperatively having a class A hearing down to 33% and patients that were 30% now they are 26%. So this is a success rate of about 59% of patients who had serviceable hearing after surgery. Another study published in 1997 in neurosurgery by Dr. Sammy again, he reviewed the same 1000 patients. All of these patients were operated on by the same surgeon using a suboccipital approach and this reviewed 732 cases with some preoperative hearing. They were able to preserve the cochlear nerve in 79% of the cases. And they preserved functional hearing overall in about 39.5% cases. Now in a selective review of just their last 200 cases, they were able to preserve some functional hearing 47% of the time. Now see here, they use a different hearing classification, there they have made up their own. So this is unlike any other that I have seen. The way you read this table, this is the number of patients preoperatively in each hearing category and they only use pure tone averages, they did not look at speech discrimination scores. And this here is the number they had each type of class represented each class of hearing postoperatively. Now what they did not know in their studies is that patients with better preoperative hearing did better postoperatively. They also looked at hearing preservation by tumor size and they found the same correlation. Here they have their own classification for tumor size, T1 to T4. Actually, the T2 size tumor had the best postoperative hearing preservation, but here they are looking at pure tone averages with hearing loss down to 80 decibels, so that is pretty pronounced hearing loss. Again the Acoustic Neuroma Association review that I presented earlier, looked at hearing as well, and of the 1,526 patients that were included, 89% of these patients presented with some hearing loss, 76% after surgery had worse hearing and 21% had hearing unchanged from the preoperative level. Other complications of surgery include trigeminal dysfunction, which has been reported to be between 2% to 4%, CSF leak, which was reported to occur 8% to 15% of the time. However, only 1% to 2% of the total group requires surgical intervention. Meningitis is reported approximately 5% of the time and mortality is very low anywhere from 0% to 1%. Radiotherapy in general has been around for over a century, but use in the management of acoustic neuromas is a process that is relatively still in its infancy. It was not until 1969 when Dr. Lexell marked the beginning of a new era of acoustic neuroma treatment by using gamma knife therapy on a patient with von Recklinghausen’s disease. Although the treated tumor started to progress after a period of observation, the case marked a beginning of an era. Before this, there were no reports of radiation treatments being used in the management of acoustic neuromas. Since that time much investigation into the efficacy of gamma knife therapy has been published into literature. However, in just 32 years there has been many advances in the diagnostic imaging, treatment planning systems and delivery of radiation which have altered the results of gamma knife therapy from those first published. In addition, trial and error has played a crucial role in the development in current treatment and protocols. So therefore an extensive review of the literature would be misleading indeed. For these reasons I have chosen to select three studies that offer relatively long-term follow-up and incorporate the most recent advances in radiotherapy of acoustic neuromas. Here are the three studies we will be looking at. They all are from 1998 or later. This study here is out of the University of Pittsburgh. This is probably the weakest study actually, as you will see Dr. Wu, I just put his name up here, but Dr. Carpenter and others are involved in this study. This is actually unpublished data that they are submitting as review of 77 cases. Dr. Prasad at the University of Virginia was published in May of 2000, reviews 153 cases with a followup of 1 to 10 years. Now as we all are experts in external beam radiation therapy following my last grand rounds, I am sure I only need to provide a cursory review of gamma knife therapy. And, unlike conventional fractionated radiotherapy, gamma knife therapy is administered in a single session typically lasting about 30 minutes +/-. They only used local anesthesia accompanied, in some instances with IV sedation, and typically multiple isocenters are used which are determined using the planning MRI and planning computer. Total dose varies conservatively between patients and institutions with the average maximal dose ranging anywhere from 25 to 50 gray and the average tumor margin dose ranging from 12 to 20 gray. But, usually they try to stay in the lower side of that range. What is nice is that the patients typically go home the same day after the treatment. Now when we are looking at gamma knife therapy versus surgical, you have to understand the treatment goals are different. The treatment goal for radiation therapy is reached if there is a cessation of the tumor growth or a decrease in the size of the tumor. In surgical therapy the goal is complete removal of the tumor and if complete removal isn’t obtained then this could be considered a failure if that was the intention of the surgeon. The first study is Dr. Fleckinger with a review of 162 patients. Of these 162 patients, which were reviewed from 1987 and 1992, 42 had undergone previous microsurgery, 11 of these 42 patients had actually had multiple previous surgeries, up to four resection attempts. What makes this study somewhat difficult to interpret is that their mode of treatment planning and radiation dosage changed throughout the treatment group, as new information and technology became available. Patients that were treated from 1987 to 1990 were evaluated using only computer tomography scans and planning was based on these scans. It was not until 1991 that they started using MRI for their treatment plans. In addition their tumor margin dose was initially 18 to 20 gray, based on initial publications out of Sweden by Dr. Norent. This dose was decreased from 16 to 18 gray at the tumor margin within the first two years of the study. and by 1992 they did decreased it down to 14 to 16 gray. So the doses are changing and the way they are planning treatments is changing, yet they grouped all these patients together and presented them in a paper. Now the reason the tumor margin dose is important is because it is well known that side effect profiles including facial nerve palsies and trigeminal nerve palsies are directly proportional to the dose at the tumor margin. Let’s first look at the rate of control, of 162 patients, there was 95% to 97% tumor control in the first three years and no further increase in tumor volume was identified in any patient after four years. Only 97 patients were available for followup after five years, and as shown in the graph or on the table, the numbers dropped off after that. Only four patients who exhibited an increase in size of their tumor represented true tumor growth, and those patients required surgical excision. Four patients of the 162 required surgical excision after radiation therapy. Now their surgeons did not describe the surgery to be any more difficult that a non-irradiated tumor; however, Dr. Brackmann reported five cases in 1995 and he stated that all the tumors he operated on were harder to resect due to prior radiation therapy. Now the point to remember from his case is that, again, only four patients required surgical intervention for tumor growth. There is no further increase in tumor volume after four years and as I said the operations were no more difficult than non-radiated tumors. If we look at facial nerve function, he reports that normal facial function was preserved in 85% of the cases. No patient with a House/Brackmann grade 1 function developed complete facial paralysis after radiosurgery, and complete facial weakness was only observed in those patients who had pretreatment House/Brackmann scores graded 3, 4, or 5. We will look at hearing. Only 32 patients had serviceable hearing prior to radiosurgery and 47% of these patients maintained their level of hearing and some degree of hearing and sound recognition was still present in 61% of the patients. In looking at their trigeminal function, it was preserved in 84% of the patients who had a normal function prior to radiosurgery. There were no trigeminal neuropathies seen in patients who had only intracanalicular tumors. Their other complications were hydrocephalus which occurred in three patients, and increased ataxia which occurred in seven patients. The next study was by Dr. Prasad, he looked at 153 patients at the University of Virginia from one to ten years and average followup of four years, 95% of his patients had a greater than a five year followup and his age range was from 18 to 88 years with an average of 60 years; 96% of these patients had only gamma knife therapy and 57 of these patients had microsurgery before they had radiation therapy. Now their doses, which they did publish, were ranging from 17 to 53 gray to the tumor and their margin doses were 9 to 20 gray with a median of 13 gray, and they used an average of 4 isocenters. First we have tumor growth he reports. He divides the patients into those patients who had only gamma knife and patients who had gamma knife following microsurgery. He showed tumor control rate of 94% in those patients treated only with gamma knife and 90% in patients treated with microsurgery first. Now what is interesting is that large tumors, those greater that 30 mm in diameter, are called large. He actually had a 95% control rate. Now the patients that had a 5 to 10 year followup, if we could just look at those 95 patients, he had a total control rate of 91% and he saw a 6% of the patients had increases in size of their tumors. This size increase can be seen, he saw, up to six years after treatment. So a lot of these studies that were initially published and looked at three or four years, he had seen growth up to six years. As we look at facial nerve function, 129 of the 153 patients were at risk for facial nerve dysfunction at time of their gamma knife. He had only three cases of facial paresis. The first case began six months after treatment and then resolved in six weeks. And the second case began a year after treatment and recovered in 18 months up to so far the time of publication, the patient report having 80% of normal function. And in the third patient, their symptomology began after six months after treatment and they ended up undergoing surgery because they thought that the tumor was growing and they didn’t realize that it could have just been a transient increase in growth. So this patient underwent surgery. So if we consider that this patient got better, and let’s just say that this patient does not get better and this patient was obviously operated on, the worse case scenario, the complication rate was 1.5%. We don’t know about the other two patients and that is why it has a zero there. Looking at their hearing preservation, they looked at 105 of 153 patients who had no residual hearing pretreatment. The remaining 48 patients were divided into these three grades, grade 1 and 2 are considered serviceable hearing, and that includes 36 patients. He assessed their hearing with both audiograms and he also assessed them subjectively, 58% had no change and 6% actually had improvement and there is decrease in hearing in 35% of the patients. Now if we looked at the patients who had serviceable hearing, 58% of them retained their pretreatment hearing levels, 42% had some deterioration and one-third of the patients actually loss useful hearing. He also found that tumor size was inversely proportional to the hearing preservation on small tumors. The results of small tumors are here. So at 75% success rate in large tumors he found up to 57% success rate. With the respect to the trigeminal nerve function, which was seen in only five patients, the onset was anywhere from one-half a year to a year and three of the five patients had complete resolution, which gives an overall permanent dysfunction rate of 1.7%. These other complications, he did not any hydrocephalus and he had no other cranial nerve symptoms. I think this is due to the fact that he is using lower tumor margin doses than the previous study. The last study I will go over quickly is done by Dr. Wu, Dr. Carpenter, and Dr. Gourmley. They started off with 77 patients treated at Hermann Hospital from 1993 to 2000. Only 49% of these patients had adequate followup. The average followup was four years, although they did extend up to 84 months. Important to know in this study is that all the tumors they treated were less than 30 mm, no large tumors. They did not provide any dosing information in their paper. If we look at the tumor control rates, they had basically a 91% control rate. Only 9% of the tumors increased in size. These patients were followed with MRI scans so this should be as accurate as we can be in this day and age. If we look at their facial nerve function, 88% of the patients had no change in their facial nerve function, 6% had improvement and 6% also had worsening of function. Now of these three patients, two of them did develop facial paralysis. And the reasons that they reported that they developed their facial paralysis is that the tumor underwent cystic necrosis, which is one of the problems with radiotherapy. If it undergoes cystic necrosis it gets bigger and you can get localized edema. In addition, cystic necrosis can also cause hydrocephalus, which is why this patient down here developed facial paralysis. However; after treatment of hydrocephalus, the patient’s nerve paralysis did resolve and he did gain some motor function back. If you look at their hearing results, they did not have many patients that had useful hearing, only 9. But of the total 49 patients that did have some sort of hearing, there was complete hearing loss in 29% of these patients. There was no change in 49% and there is improvement in 6% with an overall 55% success rate. Four of the nine patients that did have good hearing did have some hearing loss. A look at their trigeminal nerve function, they had 88% of their patients with no trigeminal symptoms, 8% had improved function, and only 4% of the patients had some kind of trigeminal neuropathy. Now there are other complications such as hydrocephalus. They had three patients that had hydrocephalus after treatment, and of the three patients, two of them did require surgical intervention. Case Presentation: E.R. is a 64-year-old gentleman seen for evaluation of a posterior fossa lesion. He has had a long-standing deafness in the right ear, which he dates to childhood. He feels it was possibly due to trauma as he was hit in the head with a baseball at that time. For two years he has noted decreased hearing in the left ear with tinnitus. He has also had episodic dizziness over that period of time, and has a chronic disequilibrium. He denies headaches or diplopia. He does admit to “fuzzy vision” and has noted some numbness in his left lower lip. Upon medical examination by his family doctor, he was found to have a large lesion consistent with an acoustic neuroma in his only hearing ear. He has no diabetes, hypertension, ischemic heart disease, or other major medical problems. The family history for acoustic neuroma and neurofibromatosis is negative. He is on no medications, and has no known drug allergies. Upon physical examination, both ear canals, tympanic membranes and middle ears are normal. The nose and oral cavity were both clear. The neck was supple without masses. Cranial nerves V and VII are intact. Romberg is negative. He has some difficulty performing tandem heel-to-toe walk. He has a profound sensorineural hearing loss in the right ear and moderately severe sensorineural loss in the left ear with an 80% discrimination. CT scan reveals a 3cm enhancing lesion in the left cerebellopontine angle and left internal auditory canal, consistent with an acoustic neuroma. The patient has been advised to have a vestibular battery to institute some form of rehab. He is currently undergoing consultation with Audiology in preparation for deafness. Treatment options will be discussed with him once further testing is complete. 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