Interview with Michael Glasscock III M.D.
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Topic: Issues Regarding Acoustic Neuromas
AO/Beck: Hi again Dr. Glasscock. It's a pleasure to chat with you, and I thank you for allowing me to pick your brain again! For the readers who may not be familiar with you, can you please give me a thumb-nail sketch of your professional background?
Glasscock: Sure. I'm a retired neurotologist. I did my fellowship in otology and neurotology at the House Group in the mid-1960s. I founded the Otology Group in Nashville, Tennessee, and worked there for 27 years until I retired a few years ago.
AO/Beck: Very good, that was brief! The focus of the discussion today is acoustic neuromas (ANs). Although these are somewhat rare in our day-to-day practice, I was surprised to read a few years ago, that based on autopsy MRI studies of asymptomatic people, about 1 in 100 people have ANs. Does that make sense, or am I remembering that sideways?
Glasscock: Actually, there were two autopsy studies done several years ago that looked at the internal auditory canal and they determined the AN occurrence rate is about 1.5 or maybe 2%. Throughout my career, I operated on about 1500 acoustic tumors. When I first started doing acoustics with Dr. House in 1965, he barely had 200 cases at that point. We reported 200 cases in 1968.
AO/Beck: Diagnosis and treatment options, as well as the philosophical approach have changed since then!
Glasscock: Exactly right. In the early days, when we first started removing acoustics, whenever we found a tumor we operated on it. Of course, before CT scans, we never knew exactly how a big a tumor was until we got there.
AO/Beck: If I recall, the radiological imaging study available at that time was the polytome and the posterior fossa pantopaque study?
Glasscock: Yes. Before polytomes all we had were petrous pyramid radiological studies. I found the Stenvers view to be the best for comparing the IAC. A suspicious Stenvers and reduced caloric would push us to a posterior fossa myelogram. Small tumors could be outlined reasonably well most of the time with pantopaque, but impossible with medium and large tumors. If we could not get the contrast material into the posterior fossa and the patient had fifth nerve findings we knew we were dealing with a medium to large tumor. When we went to surgery, we blocked out the whole day because we didn't know for certain what size lesion we were dealing with, until we started to remove the tumor. When CT came along, it was a major revelation. It was the first time we could see how big the tumor really was. Then when MRI came available with gadolinium contrast, less than 20 years ago, it was so accurate, it was simply amazing. That's when I started to change my whole attitude about operating on these tumors. We realized that you could follow them with serial MRI, and many of them simply were not going to grow.
AO/Beck: I guess we had better clarify that ANs are benign tumors, and as we stated earlier, probably some 1 or 2 percent of the general asymptomatic population has them. So what you're saying is, if the patient has a small tumor, and if it's not growing, and if it's not causing any problem relating to hearing or balance or brainstem compression etc, there is no reason to remove it?
Glasscock: Exactly. These are benign tumors and if they are not causing problems, and they are not growing, they can be observed via MRI. Many of them will remain stable, and in essence, the AN might outlive the patient! If I saw somebody 65 or 70 years old, with a very small tumor I would never recommend immediate surgery. Early on, in the 1960's or early 1970's, yes. At that time we recommended surgery as soon as we discovered the tumors. But in the 1990's, if there was an older person with a very small tumor, I would say, You have a benign tumor. It may or may not grow. However, we can do an MRI scan once a year and we'll follow it to see if it's growing. If it's growing, we can remove it. If not, we can leave it alone.
At the end of my career, I ended up with about 30 or 40 people who I was following with serial MRIs and their tumors did not change at all. Again, that was true of small tumors only. For bigger tumors, I'd recommend surgical removal, particularly if I was trying to save hearing.
AO/Beck: Dr. Glasscock, would you please tell me your thoughts about gamma knife therapy for ANs?
Glasscock: The issue I've got with gamma knife advocates is that in some respects, they're at the point we were back in the early 1960s. Many centers treat every patient they see with gamma knife. Even if the tumor stays stable and does not grow, I believe they don't know if they have a cure or not. I saw a patient in 1996 that had an MRI scan in 1991, five years earlier. Her MRI scan revealed a 1.2 cm tumor in 1991. They just argued with her and argued with her to do gamma knife. She decided she didn't want to. She wanted to follow it. I saw her five years later and it was still 1.2 cm. I told her, If you'd been treated with gamma knife you'd be one of their best cases! So my beef with them is this, as far as I'm concerned they're 40 years behind philosophically. What they really ought to do is MRI these patients with small tumors and follow them for a period of time to make sure the tumors are growing. With the MRI you can see a one millimeter difference. Only then, should they treat them. Larger tumors, 2 cm or greater, should be removed surgically, that's my belief.
AO/Beck: What is the down side, what are the risks of gamma knife therapy?
Glasscock: Good question. Suppose the tumor does grow. If it does, and there are certainly documented cases where patients have had gamma knife or linear accelerators, and the tumors do grow, then when the tumors are removed surgically, it is very difficult to preserve the facial nerve.
AO/Beck: I believe the tumor also becomes more adherent to the brain and the cranial nerve tissue too?
Glasscock: Yes, that's a big issue as well. According to the House Group, after a tumor has received gamma knife therapy, it becomes very adherent and surgical removal is more difficult. I have no problem with gamma knife if it is used scientifically. I have three otologist friends who have been trained in the use of the gamma knife. They are making sure the tumor grows and only then do they treat the lesion. But those centers that treat all small tumors, and say they get good results before they know the natural course of the tumor, are, I believe, shortsighted and ill advised. Again, a lot of those tumors will not grow.
AO/Beck: Let's talk about your preferred surgical route. I suspect the translabyrinthine craniotomy (TLC) approach is the approach of choice?
Glasscock: Absolutely. Certainly for any tumor over 1.5 to 2 cms if there's no hearing, TLC is a beautiful procedure. The thing people don't understand about TLC is that if you have a really big tumor you can always do a combined TLC with a suboccipital approach. But the biggest advantage of the TLC approach, which a lot of the neurosurgeons miss, is that you can identify the facial nerve very accurately in the lateral part of the internal auditory canal and you can dissect the facial nerve off the anterior part of the tumor under direct vision. You cannot do that from the suboccipital approach. I've done a lot of suboccipital procedures and you simply cannot identify and protect the facial nerve as well as you can with TLC.
AO/Beck: What are your thoughts on neurotologists that remove ANs by themselves, without neurosurgeons?
Glasscock: Of course it varies with the individuals and their expertise. I always trained my fellows to immediately start working with a neurosurgeon once they entered practice. I believe the team approach is the best one for the patient.
My opinion is, unless you do a neurosurgical residency and you've faced neurosurgical complications, such as increased intercranial pressure, brain stem infarctions, all those things that can occur during brain surgery, trying to do it by yourself as a neurotologist makes no sense. I always taught the neurotology fellows to work hand in hand with a neurosurgeon. I also taught them that both surgeons should know how to do all parts of a procedure. I taught my neurosurgeon how to do a labyrinthectomy and mastoidectomy, and he taught me how to work on the brainstem. If our patient had a problem post-operatively, the neurosurgeon was experienced in those complications, he knew the case, had been there, had worked on the brainstem, and knew exactly what was going on. Frankly, there are some very good neurotologists who do AN surgery by themselves. That's fine, until they have a complication and they have to call in a neurosurgeon who doesn't know anything about the patient, has never seen the individual before, and has never been in the patient's posterior fossa. The neurosurgeon and the patient are at a terrible disadvantage.
Of course, there were times when I would take out the tumor by myself, but only if it was a very small tumor, and only if the neurosurgeon was in the room and only if he said go ahead and take it out. The neurosurgeon being there at the time of the surgery is very important. And anybody that says they don't have complications during and after acoustic tumor surgery is lying through their teeth.
AO/Beck: Please tell me your thoughts on hearing preservation during AN removal?
Glasscock: Frankly, I'm amazed by some of the reports I've seen in the literature regarding hearing preservation. When I was doing posterior fossa surgery, I was an average surgeon, and frankly I had a terrible time preserving hearing. I'd go middle fossa, posterior fossa, I'd monitor everything, I would use all kinds of solutions to dilate the blood vessels and the best I could ever do consistently was about 30-35%. But aside from the percentage of people who have their hearing preserved, is the issue of the quality of hearing saved. Suppose you have a patient with a 0 dB pure tone level with 100% discrimination in the left ear. You perform a successful surgical procedure on the right and preserve an 80 dB hearing loss with 0% discrimination in the operated ear. In my opinion, you have not helped that individual with the hearing in the right ear! They will not be a successful hearing aid candidate, and when they go into a noisy restaurant they're not going to be able to hear very well. They're not going to be able to pick up the direction of sound with the best hearing aid. Any time you preserve hearing you have a trade off. You may pick a riskier surgical approach, or perhaps you run the risk of a recurrence because you're reluctant to take the entire tumor off the auditory nerve. There was a paper years ago on stapedectomy by Gene Derlacki that showed if you couldn't get within 15 dB of the better ear you did not help the patient unless they continued to wear a hearing aid. Because even though the surgery was a success, even if you improved the hearing in the operated ear, the patients continued to have problems and did not appreciate their hearing gain. So I think there's a lesson there about hearing preservation surgery as it relates to ANs.
AO/Beck: Once again Dr. Glasscock, I want to thank you for your insight and thoughts about issues related to ANs, and the time you've afforded me today.
Glasscock: Thanks Doug, it really is fun working with you too, and I appreciate your letting me throw some of my personal thoughts and reflections out there for general consumption! Maybe some of these discussion will impact our colleagues and allow them to think of these issues from alternative viewpoints.
AO/Beck: I think that's likely Dr. Glasscock!
Glasscock: Sure. I'm a retired neurotologist. I did my fellowship in otology and neurotology at the House Group in the mid-1960s. I founded the Otology Group in Nashville, Tennessee, and worked there for 27 years until I retired a few years ago.
AO/Beck: Very good, that was brief! The focus of the discussion today is acoustic neuromas (ANs). Although these are somewhat rare in our day-to-day practice, I was surprised to read a few years ago, that based on autopsy MRI studies of asymptomatic people, about 1 in 100 people have ANs. Does that make sense, or am I remembering that sideways?
Glasscock: Actually, there were two autopsy studies done several years ago that looked at the internal auditory canal and they determined the AN occurrence rate is about 1.5 or maybe 2%. Throughout my career, I operated on about 1500 acoustic tumors. When I first started doing acoustics with Dr. House in 1965, he barely had 200 cases at that point. We reported 200 cases in 1968.
AO/Beck: Diagnosis and treatment options, as well as the philosophical approach have changed since then!
Glasscock: Exactly right. In the early days, when we first started removing acoustics, whenever we found a tumor we operated on it. Of course, before CT scans, we never knew exactly how a big a tumor was until we got there.
AO/Beck: If I recall, the radiological imaging study available at that time was the polytome and the posterior fossa pantopaque study?
Glasscock: Yes. Before polytomes all we had were petrous pyramid radiological studies. I found the Stenvers view to be the best for comparing the IAC. A suspicious Stenvers and reduced caloric would push us to a posterior fossa myelogram. Small tumors could be outlined reasonably well most of the time with pantopaque, but impossible with medium and large tumors. If we could not get the contrast material into the posterior fossa and the patient had fifth nerve findings we knew we were dealing with a medium to large tumor. When we went to surgery, we blocked out the whole day because we didn't know for certain what size lesion we were dealing with, until we started to remove the tumor. When CT came along, it was a major revelation. It was the first time we could see how big the tumor really was. Then when MRI came available with gadolinium contrast, less than 20 years ago, it was so accurate, it was simply amazing. That's when I started to change my whole attitude about operating on these tumors. We realized that you could follow them with serial MRI, and many of them simply were not going to grow.
AO/Beck: I guess we had better clarify that ANs are benign tumors, and as we stated earlier, probably some 1 or 2 percent of the general asymptomatic population has them. So what you're saying is, if the patient has a small tumor, and if it's not growing, and if it's not causing any problem relating to hearing or balance or brainstem compression etc, there is no reason to remove it?
Glasscock: Exactly. These are benign tumors and if they are not causing problems, and they are not growing, they can be observed via MRI. Many of them will remain stable, and in essence, the AN might outlive the patient! If I saw somebody 65 or 70 years old, with a very small tumor I would never recommend immediate surgery. Early on, in the 1960's or early 1970's, yes. At that time we recommended surgery as soon as we discovered the tumors. But in the 1990's, if there was an older person with a very small tumor, I would say, You have a benign tumor. It may or may not grow. However, we can do an MRI scan once a year and we'll follow it to see if it's growing. If it's growing, we can remove it. If not, we can leave it alone.
At the end of my career, I ended up with about 30 or 40 people who I was following with serial MRIs and their tumors did not change at all. Again, that was true of small tumors only. For bigger tumors, I'd recommend surgical removal, particularly if I was trying to save hearing.
AO/Beck: Dr. Glasscock, would you please tell me your thoughts about gamma knife therapy for ANs?
Glasscock: The issue I've got with gamma knife advocates is that in some respects, they're at the point we were back in the early 1960s. Many centers treat every patient they see with gamma knife. Even if the tumor stays stable and does not grow, I believe they don't know if they have a cure or not. I saw a patient in 1996 that had an MRI scan in 1991, five years earlier. Her MRI scan revealed a 1.2 cm tumor in 1991. They just argued with her and argued with her to do gamma knife. She decided she didn't want to. She wanted to follow it. I saw her five years later and it was still 1.2 cm. I told her, If you'd been treated with gamma knife you'd be one of their best cases! So my beef with them is this, as far as I'm concerned they're 40 years behind philosophically. What they really ought to do is MRI these patients with small tumors and follow them for a period of time to make sure the tumors are growing. With the MRI you can see a one millimeter difference. Only then, should they treat them. Larger tumors, 2 cm or greater, should be removed surgically, that's my belief.
AO/Beck: What is the down side, what are the risks of gamma knife therapy?
Glasscock: Good question. Suppose the tumor does grow. If it does, and there are certainly documented cases where patients have had gamma knife or linear accelerators, and the tumors do grow, then when the tumors are removed surgically, it is very difficult to preserve the facial nerve.
AO/Beck: I believe the tumor also becomes more adherent to the brain and the cranial nerve tissue too?
Glasscock: Yes, that's a big issue as well. According to the House Group, after a tumor has received gamma knife therapy, it becomes very adherent and surgical removal is more difficult. I have no problem with gamma knife if it is used scientifically. I have three otologist friends who have been trained in the use of the gamma knife. They are making sure the tumor grows and only then do they treat the lesion. But those centers that treat all small tumors, and say they get good results before they know the natural course of the tumor, are, I believe, shortsighted and ill advised. Again, a lot of those tumors will not grow.
AO/Beck: Let's talk about your preferred surgical route. I suspect the translabyrinthine craniotomy (TLC) approach is the approach of choice?
Glasscock: Absolutely. Certainly for any tumor over 1.5 to 2 cms if there's no hearing, TLC is a beautiful procedure. The thing people don't understand about TLC is that if you have a really big tumor you can always do a combined TLC with a suboccipital approach. But the biggest advantage of the TLC approach, which a lot of the neurosurgeons miss, is that you can identify the facial nerve very accurately in the lateral part of the internal auditory canal and you can dissect the facial nerve off the anterior part of the tumor under direct vision. You cannot do that from the suboccipital approach. I've done a lot of suboccipital procedures and you simply cannot identify and protect the facial nerve as well as you can with TLC.
AO/Beck: What are your thoughts on neurotologists that remove ANs by themselves, without neurosurgeons?
Glasscock: Of course it varies with the individuals and their expertise. I always trained my fellows to immediately start working with a neurosurgeon once they entered practice. I believe the team approach is the best one for the patient.
My opinion is, unless you do a neurosurgical residency and you've faced neurosurgical complications, such as increased intercranial pressure, brain stem infarctions, all those things that can occur during brain surgery, trying to do it by yourself as a neurotologist makes no sense. I always taught the neurotology fellows to work hand in hand with a neurosurgeon. I also taught them that both surgeons should know how to do all parts of a procedure. I taught my neurosurgeon how to do a labyrinthectomy and mastoidectomy, and he taught me how to work on the brainstem. If our patient had a problem post-operatively, the neurosurgeon was experienced in those complications, he knew the case, had been there, had worked on the brainstem, and knew exactly what was going on. Frankly, there are some very good neurotologists who do AN surgery by themselves. That's fine, until they have a complication and they have to call in a neurosurgeon who doesn't know anything about the patient, has never seen the individual before, and has never been in the patient's posterior fossa. The neurosurgeon and the patient are at a terrible disadvantage.
Of course, there were times when I would take out the tumor by myself, but only if it was a very small tumor, and only if the neurosurgeon was in the room and only if he said go ahead and take it out. The neurosurgeon being there at the time of the surgery is very important. And anybody that says they don't have complications during and after acoustic tumor surgery is lying through their teeth.
AO/Beck: Please tell me your thoughts on hearing preservation during AN removal?
Glasscock: Frankly, I'm amazed by some of the reports I've seen in the literature regarding hearing preservation. When I was doing posterior fossa surgery, I was an average surgeon, and frankly I had a terrible time preserving hearing. I'd go middle fossa, posterior fossa, I'd monitor everything, I would use all kinds of solutions to dilate the blood vessels and the best I could ever do consistently was about 30-35%. But aside from the percentage of people who have their hearing preserved, is the issue of the quality of hearing saved. Suppose you have a patient with a 0 dB pure tone level with 100% discrimination in the left ear. You perform a successful surgical procedure on the right and preserve an 80 dB hearing loss with 0% discrimination in the operated ear. In my opinion, you have not helped that individual with the hearing in the right ear! They will not be a successful hearing aid candidate, and when they go into a noisy restaurant they're not going to be able to hear very well. They're not going to be able to pick up the direction of sound with the best hearing aid. Any time you preserve hearing you have a trade off. You may pick a riskier surgical approach, or perhaps you run the risk of a recurrence because you're reluctant to take the entire tumor off the auditory nerve. There was a paper years ago on stapedectomy by Gene Derlacki that showed if you couldn't get within 15 dB of the better ear you did not help the patient unless they continued to wear a hearing aid. Because even though the surgery was a success, even if you improved the hearing in the operated ear, the patients continued to have problems and did not appreciate their hearing gain. So I think there's a lesson there about hearing preservation surgery as it relates to ANs.
AO/Beck: Once again Dr. Glasscock, I want to thank you for your insight and thoughts about issues related to ANs, and the time you've afforded me today.
Glasscock: Thanks Doug, it really is fun working with you too, and I appreciate your letting me throw some of my personal thoughts and reflections out there for general consumption! Maybe some of these discussion will impact our colleagues and allow them to think of these issues from alternative viewpoints.
AO/Beck: I think that's likely Dr. Glasscock!
