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Grand Rounds-The Oral Boards Review: Peripheral Nerve Tumors and Neuropathic Pain

Robert Spinner

November 01, 2011


- The second part of our review for peripheral nerve disorders has been divided into two. Eventually there will be a third part to this review which will include peripheral nerve tumors. Thank you.

- All of that aside, I'd like now to say a few words about nerve tumors, and help you distinguish benign from malignant and help with localizing some of these. Now, as I've mentioned, imaging is very important, especially on your boards. And I would just tell you one hint. Any area that you can localize, producing focal pain in an unusual site, or that causes radiating paresthesias that's not the carpal tunnel, or the cubital tunnel, for example, should be imaged. So for example, if somebody had a peroneal nerve-type palsy I would percuss along the nerve. If there was no trauma, then I'm thinking about an entrapment at the fibula neck. If, however, the patient localized to the thigh rather than the fibular neck, then I want to make sure the thigh is part of the imaging. So, for example, if a patient told you they had foot drop, you examine them, they have sciatic neuropathy, part of their history was when they sit, their symptoms are provoked, then I want to make sure that I test their buttock by provoking that as a pain trigger. I want to do a Tinel's sign there. I want to do various hip motions, and eventually I want to image it. And lo and behold, I bet they have a mass in their buttock region. Whether they're finding, or telling you that it's Tinel's sign. Any mass associated with a nerve that is detected on your clinical exam should be imaged. Assuming everything is a lipoma or a lymph node, or a ganglion cyst when they're in unusual spots is a shortcoming. I'll just leave it at that. I would get some MRI, or even an ultra-sound. Now, a basic fact that really is simple, that is really not harped on loudly enough is the fact that most, almost all, benign nerve-sheath tumors present with some neurologic symptoms, but without deficit. Let's say that the opposite way. It's exceedingly rare for a patient with a benign nerve-sheath tumor, that's a classic nerve-sheath tumor, that that patient would have a deficit of weakness at the time of onset. That's very important. So if you have a patient with symptoms but with a normal exam, and you image them, and you review it with the radiologist, and they say it's a nerve-sheath tumor, then you're down to a schwannoma or nerve hydroma. Then you need think about syndromes. If there's no syndrome and it's solitary, then it's usually a schwannoma, almost always, and that patient has a very good outcome with surgery, if that's necessary. Now let's distinguish that from someone who presents with neurologic symptoms and neurologic deficit. That would be rare for a benign nerve sheath tumor. It would not be rare for a malignancy, so most commonly would be a malignant peripheral nerve sheath tumor, but it could also be metastatic or perineural spread. It could be an extraneural malignancy, like a sarcoma, pressing on the nerve. These patients should have more pain. They might have systemic illness. They would have progressive, rapid deficits, a mass and an ugly-looking MRI scan, typically. So I think the history and the physical exam are very important in your getting between the benign nerve sheath tumor and a malignant one. All you have to do is ask the radiologist, was it a benign nerve sheath tumor? That's as far as they'll probably get, because after that, if it's regular, it's probably benign. If it's a little bit inhomogenous or not quite perfectly round, or larger, then it might be malignancy. Where things get a little bit complicated, but I think are really quite clear, are there are rare lesions that are benign lesions but they're not benign nerve sheath tumors. It is a lesion that I've been particularly interested in, called a intraneural ganglion cyst, where there's cyst fluid in the nerve that causes a mass. The difference is this signals like cyst. I'll show you a case because I think this is testable, I think it's important because there's now surgical treatment that can be directed and cure it. So an intraneural lesion, most commonly a cyst, most commonly a damaged peroneal nerve causing a foot drop, this is characteristic of a treatable, curable lesion. That's not malignant at all, but some people still think it is, and that's why they're doing big resections. The other lesion, like I told you with the the posterior interosseous nerve, is an extraneural benign lesion. This would be like a ganglion or lipoma near the posterior interosseous nerve causing a sandwich of the tumor against the posterior interosseous nerve, against the arcade of Frohse. It's creating a mini compartment. Now there are some syndromes that you need to know about that I'm gonna simplify for you based on a peripheral nerve surgeon's perspective. And if one is 1 in 3000 people who know about the cutaneous stigmata and sort of a laundry list of how many things you need, café-au-lait spots, upraised lesions, axillary freckling and the like. These patients have neurofibromas, they can have plexiform neurofibromas, and these plexiform neurofibromas can transform into malignancies. They typically don't have schwannomas. These may be somewhat harder to take out. The plexiform neurofibromas, as you'll hear, are usually almost impossible to cure from a major nerve. It may be able to debulked sufficiently enough. NF-2, these patients don't have the stigmatas of NF-1. We know about them because of the acoustic neuromas. These patients, when they have peripheral nerve lesions, they have schwannomas. They don't have neurofibromas, and, unless they were radiated, don't have sarcomas, usually. NF-2 is 1 in 30,000 people. So it Schwannomatosis. This is the new kid on the block. This is part of the spectrum of the family of NF-related diseases. There are no cutaneous stigmata. They don't have acoustic schwannomas, but they can have schwannomas anywhere else and on rare occasions, even intracranially. Let's talk about the benign intraneural nerve sheath tumors. Most commonly in isolation, they're schwannomas. They can be neurofibromas, especially syndromic with NF-1. Plexiform lesions in NF-1 is pathognomonic. These are not uncommon for a neurosurgeon. schwannomas and neurofibromas, as I mentioned, typically present with some pain or paresthesias, but not typically weakness. What we've learnt from Dr. Klein's large series and huge experience over 30 years is that they can often resected safely. Our cartoon from one of our publications shows a schwannoma being resected. This is a nice operation. In fact, it's easier than other neurosurgical procedures when done in the periphery because I'm able to mobilize the nerve and then map it out by looking where the fascicles are, where the bare area is. Here the bare area is bulging eccentrically. Make a longitudinal epineuratomy away from the fascicles and the bare zone and then find the single entering and exiting fascicle, resect that, after Klein-- This would not cause stimulation or induction into your target muscle and they can be resected. About 80 - 90% of the time in his experience, function can be preserved. So here you do whatever you can to save the nerve. This is a nice and gratifying operation. Here's a good example of a patient who has a schwannoma. The imaging can be consistent with a speckled type of appearance. This is good for a benign nerve sheath, especially one that's round. You can see the entering nerve on many cuts. This is in line with the median nerve. The patient found this mass while putting on soap in the armpit. Here, when percussing in the axilla, one caused a radiating Tinel's sign into the fingers. Function was normal, there was no weakness. Though I thought we could watch this, the patient was worried, she had a history of carcinoid syndrome. Most people don't believe in preoperative testing, or a biopsy, percutaneously of what would appear to be a benign lesion, so I resected this. Approximated this control of the median nerve had obtained. Just like the cartoon, the median nerve is identified. A continuous branch was seen and protected. The eccentrically-placed mass is displacing the fascicles of the median nerve. Here you can see the tumor, map it out. Here's the bare zone, a little bit vascular, make an epineurotomy, find a entering tube, single or double fascicles. It's a stealth mission, the rest of the nerve is left alone and is intact, working normally without that benign nerve sheath tumor. schwannoma. Patient can have more than one tumor here. Patient presents with symmetric or bilateral tumors, involving the brachial plexus. When one is symptomatic or large, you can take them out. Obviously there are lots of factors that go into the desire to take them out. On your exam, the patients could become more and more symptomatic, or they'll be growing. There are numerous advantages to taking out a tumor when it's small. It's easier to take out, you don't have to worry about it growing and follow up with serial exams over the course of a lifetime. You have definitive pathology. Neurofibroma, for example, can transform, so here we have not only a benign lesion, but if it were a nerve fibroma, you would need to remove any possibility of malignancy. There are lots of reasons to take it out, but most importantly, it's for pain control or for size. This patient with schwannomatosis presents every year with different symptomatic lesions. This one is involving a branch of the obturator nerve and then the sciatic nerve and then here the trigeminal nerve, but not the acoustic nerve. The vestibular nerve and acoustic fibromas wouldn't be present in patients with schwannomatosis, but on occasion, can be present... Oh sorry, they wouldn't be present in schwannomatosis, they would and could be present in NF-2. We're learning that schwannomas don't have to be single fascicles. There are more fascicles that can be involved and these can give different appearance, including a dumbbell appearance or a multifascicular appearance, and that's why you still have to have your horns up and your antennas up if somebody has a funny-looking scan. And we just saw one last week, where a patient had what was a plexiform schwannoma. Their multiple fascicles were affected. If you take out multiple tumors, you're going to have deficit because there is little nerve left. neurofibromas used to be thought to be unresectable because they were thought to be more concentric and involved more of the nerve. Several fascicles are going in, several fascicles are going out, so Dr. Klein has shown over his lifetime that he's able to preserve the function many times up to 70 or 80%, maybe a little bit lower in NF-1 related patients. Again, you need to think about, in these types of patients, the small transformation rate into malignancy. Not all neurofibromas are concentric. Here you see a patient, in fact, with a lesion involving the sural nerve. This was a patient with NF-1. There was no question this was neurofibroma, but yet it really looked like a single fascicle and was able to save the sural nerve on this patient whom I really thought was going to be resectomy. Another patient with a sciatic set of lesions. Again, eccentric neurofibromas. The difficult one is the plexiform neurofibromas. Every nerve can be affected, every fascicle can be affected. You're watching for malignancy, you're following patients with NF-1. The patient presents with a little deficit because now every fascicle's involved, there's some concern because pain is worse. Been asked about doing a biopsy or resection. I would say in a case like this, which fascicle, which part of the tumor are you thinking is malignant. Here it would be impossible to know. On occasion, though, there's one fascicle or one dominant nodule that becomes protuberant or worrisome. That's different, and you can debulk these. Here, oftentimes we watch these and educate the patient about the problem. So here for example, is patient with NF-1 who has lesions involving the sciatic nerve complexes from stem to stern, with some pain, some deficit. There's not much you can do except follow this and treat them empirically, with medication, but there's no way that you could determine that this one, that little nodule that's causing the pain. Here you can see on the cross section that every part of the nerve is being affected. I wanted to talk about this intraneural ganglion cyst, because like I say, there's been some progress regarding the understanding of its pathogenesis and treatment. It used to be thought to be curious disorder, but now, in fact, it's not curious. It's interesting, but fixable and understandable. Patients present characteristically with a foot drop. Oftentimes, it's predominantly a deep peroneal innervative loss, so dorsal plexion, toe extension may be paralyzed, they're severely weak. Eversion, superficial peroneal nerve, is unaffected almost always. Due to this, you can confirm that clinical localization will be injury to the fibular neck. Again, unusual localization, it's not carpal tunnel, it's not cubital tunnel syndrome. Get an image with an MRI, you would be able to see the pathology. If you view this type of image with your radiologist, this is cyst. The radiologist will tell you that's it's irregular, it's benign, it's not a nerve sheath tumor. People thought, could this be some sort of transformation from a cystic schwannoma? It's not. These are connected to the joints. The peroneal nerves are, these lesions are always in this location. They're connected via the articular branch, from the superior tibial figure eight joint into the articular branch into this side of the common peroneal nerve, and this common peroneal nerve, it's fibers are here and deep, so when it does this, it goes into this part of the nerve always, and that's why the deep is affected before and preferential to the superficial. In fact, there's never been a case of a superficial peroneal nerve lesion in this location because the presentation is pathognomonic. The treatment here, in order to prevent the very high recurrence rate that had been described previously, the recurrence can be eliminated. All you need to do is cut this little articular branch. And I'll show you how obvious that is at surgery when we look for it and you know about it. The difference is that most people know that the common peroneal nerve divides into a deep and superficial branch. Again, this is the foot and toe extensors, this is the evertors, but very few people know that a very regular articular branch that goes to the joint at that level, but this is underneath the peroneus longus muscle, where the nerve gets entrapped, the resection is difficult to do. This is a cadaver specimen, but this corresponds with our MRI appearance of cysts in the articulation of the superior tibial fibular joint, extending into that branch and up. Here's an operative appearance of a recent case. Here's the common peroneal nerve. Here's the cyst. The difference is that the cyst is still going. This is the peroneus longus fascia. The joint is clear over here. It's difficult, very few people know to look here. And you may think the cyst has stopped here, but in effect, if you trace it through the fascia and through the muscle, you can follow this branch and in fact, it can be a skip lesion where this may appear normal, but in fact, you can see that this is still cyst and if you disconnect it right here at the joint, you would still get the rush and evacuation of cyst material. Really, that's all you need to do, you don't need to resect this. The cyst itself can just be decompressed via a little slit. In fact, if you just cut that, it'll drain out here and go away. You don't need to take out the cyst as many people still do, but if you cut this, the cyst is gone. You never need to treat it again. You just need to be aware of it, image it, identify it and then, treat it. Now that's benign intraneural. I wanna now talk about benign extraneural cysts, because as I told you and I showed you the posterior interosseous nerve case, these can compress and constrict a nerve, especially causing kind of a mini compartment-type of pressure. And here, as I showed you with that case, you image it, then you know what you're dealing with. You see the nerve anatomy, you make a diagnosis, because these in fact, can be diagnosed without tissue. Ganglia appear certain ways, lipomas appear certain ways on imaging. You protect the nerves and take out the tumor. Here's an example of a benign cyst. Patient presented with foot drop, but the difference between this ganglion and the one I just showed is this is round, it's compressing the nerve, it's not in the nerve. This is extraneural, compressing the nerve. The other one was intraneural. They're both joint-derived. Here, you can do a similar type of operation and take out the cyst or you can disconnect, but here, most people would think that the joint is unusual and there's a hole in the joint, so some people might do a joint-related procedure. That's beyond what you need to know. I did want to now spend a moment talking about malignancy, because I think this is a completely different history. Let's show a case, patient may have NF-1. They may tell you about that, they may tell you that they don't know, some patients don't know they have NF-1, present with a new mass. A typical history would be a person with a new mass, now weakness that's progressive and severe, and severe pain that's worsening, refractory with medication. Could you get pain that's bad, refractory with medications, with a benign tumor? Sure, but you wouldn't get this history of weakness associated with it like that where you have a worrisome cancer pain. Here would be a patient. Now, I might not tell you that he had NF. This was being gentle. Here, you might be asked what these are or if you didn't know them, they might lead to them afterwards that you can see. Cutaneous neurohydromas, some axillary freckling, café-au-lait spots, no family history in this case. This patient presented with this large, immobile mass. If you took a history, there would be a large immobile mass. Benign tumors are mobile, transversely but not up and down. And here, you'd have severe weakness. I'd ask you what muscles and ask you about carpal tunnel, then ask about extrensics and I could tell you that this patient had that benediction sign. So this patient would be trying to make a fist, he can't. These are paralyzed, the thumb is paralyzed, then sensory loss, pain, big mass here and then stigmata of NF-1. This is a worrisome history. Image it. This, while it was called at our institution, a indeterminate, but likely benign, mass, has this area that could be considered similar to necrosis. It's not quite perfectly regular, it's got some nooks and crannies, PET scan was positive, PET scan being positive, is indeterminate, but in all these areas where this mass is readily accessible, I'm worried about a malignancy. I did a percutaneous biopsy, it was malignant. I staged the patient, I then got the tumor team involved, and we made recommendations, and at our institution, the patients with malignancies first suspect them. Rapidly enlarging mass, increasing pain, increasing deficit, especially with NF. That's a great test question. But here, regardless of what you do, you want to tell your examiner or your patient, that here, I am concerned and now can diagnose you with a malignancy. This is completely different than trying to take out the tumor with maintaining function 90% of the time. Here I'm trying to save lifetime because survivals are 50% at five year. Here you don't want a nerve-saving operation as part of the schwannoma-type operation. You wanna do a sarcoma-type of operation. At our institution, we'll come back here to see this in a second, we do neoadjuvant therapy in an attempt to shrink tumors. So we would radiate, possibly give chemotherapy, try to do a nerve-sparing, limb-sparing operation as best as one can, but you need to do a definite operation with a wide resection. So limb-sparing, you save whatever nerves you can in the neighborhood, but the nerve of origin is gonna have to go and then you can think about reconstructing it either with some type of nerve operation or a tendon transfer, but the bottom line is that you need to be aggressive, get rid of the tumor with cancer-type of operation, treat them aggressively, and then think about reconstructing the deficit. But you need to counsel them completely different. If I were an examiner, I think this would be a very fair question, because most people, when I ask them about this, they sorta go into Dr Klein, 80 - 90% schwannoma type of thing. I ask them, do they think that the patient's deficit will get better, they kinda say yes. That's not true at all. In fact, when you take out the schwannoma, you're trying to save function. Very rarely do they have a deficit. If they have a deficit, most likely they wouldn't get better. So the sarcoma-type of operation, the MPNST is derived at, is a different operation, you're trying to save the life. Now on the previous slide, I did talk about risk factors. There are three that are known. They can occur spontaneously, just bad luck. They can occur a decade or so after radiation in the area, that's not unusual, and they can be related to NF-1, and they're thought to be due to the number of tumors and the surface area of those tumors. But in general, these patients get aggressive operations, wide resections, either functional or physiological amputations. Here's ones of the brachial plexus. Finally, let's just end briefly talking about neuropathic pain, because I do think this is an important part of your armamentarium and an important part of what a neurosurgeon should know and deal with. Now, with neuropathic pain, how do you know that this is this rather than mechanical pain, and I think you'll know it when you see it or you'll know it when you hear it. Patients describe this burning, lancinating pain, electrical in nature, it's a nerve pain. And I think, for all intents and purposes, you as a neurosurgeon for your boards need to know two different things. One is the concept of a nerve or a neuroma in continuity. Some, similar to the ones we saw before, earlier in the first talk, where the nerve is injured, but in continuity, that's a neuroma, and it's a painful neuroma. Verse a neuroma from a stumped neuroma or a cut nerve. They're both neuromas but you wanna treat them a little bit differently and work them up a little bit differently. The history can often tell you that you're suspecting these, whereas for example, a Morton's neuroma is not this neuroma, it's actually a nerve in continuity that's been injured, but because it's been injured so bad, people call it a neuroma, ambiguous nomenclature. First, how to treat. Well, number one is diagnose it. So again, go back to your four legs on the table and the Michelle Cleo metaphor that I discussed. So diagnose and recognize early. Pain, the lancinating pain with neurologic symptoms and a focal, localizable Tinel's sign. How to manage. Well, I think the first thing is to avoid nerve injury whenever you can. So I think knowledge of the anatomy, we talked about carpal tunnel syndrome, we talked about some of those small branches you saw of my decompression of the ulnar nerve at the elbow. Medial elbow pain with cubital tunnel, might give you numbness in the proximal form, that's a known problem after ulnar nerve decompression or transposition. Those skin nerves are there, you need know about them. So plan your incisions accordingly, use good technique and then sometimes you need good luck. And sometimes you need to not paint yourself in a corner by having good foresight in order to prevent it. So where to place your incisions, and that's why I was talking about the typical topographical landmarks, even with carpal tunnel. An easy operation can lead to painful neurologic screwup. But I think you should have an algorithm for nerve pain for your boards. First of all, you make your diagnosis and then you treat. So pharmacologic options, you know about the ladder of treatment, whether it's antiepileptics, or antidepressants, or narcotics, or nonsteriodals, whatever you want to use, you have to have a pharmacological treatment plan that works. Behavior modification is important, because this is a multi interdisciplinary approach, including therapy, desensitization exercise, psychologists, we've all taken care of pain patients. For surgery, once you've availed nonoperative measures, there are different things one could try that I just want to give you some type of algorithm. We talked about neuropathic pain. Now, for example, with lateral femoral cutaneous nerve compression, decompression can be done, for example, with a neurolysis. You're releasing the inguinal ligament, that would be enough for many people, some people move down and do a neurectomy for that, either primary or if this first operation fails. That's controversial. You can't do a neurectomy of a mixed nerve that's working there, so you'd have to be either a sensory nerve or a long-term nerve that's not working, but I'd be reluctant obviously to do that on someone's painful mixed motor nerve. Now, reconstruction is advocated by several, so for example, if you had that radial nerve injury that I showed in the arm following the lipoma resection that ended up in schwannoma by the family physician. I did a primary repair. Getting rid of a neuroma can oftentimes help pain, so doing a nerve repair or graft, that's a comprehensive approach for the function, may help with the pain. Sometimes with pain or bad skin coverage, you have to think about flaps and good tissue beds. Sometimes when people have neuropathic pain, it could be a small tumor that could be resected. All of these are ways of doing corrective operations. On the flip side, there are either chemical or surgical types of neurectomies. Old time, years ago, we used to do methanol, cryo ablations, but again, that's one thing you can do and that's one of the things that they-- Surgical option is a reasonable one. And all these types of nerve operation, in my experience, work about 50% of the time, after I've done a comprehensive workup. The workup always entails nerve blocks, sometimes even we'll dilute saline, placebo block. Now, like we talked about, neurectomy can be done with either open or percutaneous means. Neuromodulation is another way, either for a stump neuroma or a neuroma in continuity. The advantage is that it's reversible, nondestructive. Screening may help. Localization doesn't always have to be known, you can do regional ones. There are other sites besides peripheral nerve, as you know, spinal nerve, spinal cord, motor cortex. You can do augmentation, modulation using drugs. And let's just show an example. I think one area of pain you need to know about is pain after a sural nerve harvest. I think if I were your examiner and I had you harvest some sural nerve, I'd ask you where the incision was, whereat the deficit would be, and then I would give the patient terrible pain. You got a great result functionally, but he's had debilitating pain, how would you manage? So I'd want you to go through the algorithm of medical treatment, maybe a block or two for diagnosis and then telling me what you're gonna do here. Another neurectomy and placing the cut end in a better place, deep away from the joint in a muscle, that would a good solution. Some people place cut ends of nerves in bone, and I think most people have moved away from that. For example, various nerves can be injured after hernia surgery. They're listed below: the ilioinguinal, iliohypogastric, genitofemoral, lateral femoral cutaneous nerve. I think the courses of these nerves should be known as well as their distributions and the areas that might be painful or affected in given individuals. With hernia surgery, the most common, at least in my experience, is the ilioinguinal nerve. But I think one needs to distinguish that from these other nerves, which are at least in the territory. Other surgeries in the area can also affect different nerves. The spine surgeons are well familiar with the lateral femoral cutaneous nerves as we discussed, either from bone grafting techniques or from positional ones. Other nerves might be related to Pfannenstiel-type approaches after Cesarean sections. So I think one should have an algorithm about how to treat patients with this problem. Here's a patient who had a hernia repair, who ever since the surgery, woke up with lancinating, electrical pain that went into the testicle and scrotum area, with groin pain, and here the pain went away with blocks, specifically designed at the ilioinguinal nerve, so after failed non-operative treatment, treatment ensued and here you can see scarring present in the region of the external oblique and there's the stump neuroma, which was identified and then trimmed back proximally and allowed to retract back into, perhaps, a better bed, where this new neuroma would obviously form, but perhaps would be in a better location and would not be symptomatic. You have to know that neuromas form after any nerve is cut, but the trick is to try to convert this painful trigger into a asymptomatic neuroma that's in a better position. Here's a different patient, who you can see, had had some ankle injury here, had some surgery, then some more surgery, then some more surgery, and before you knew it, there were about 10 operations on this patient for a tibial neuralgia. Her function wasn't bad, so we can't cut the nerve here, or I wouldn't advise it, but eventually I explored, found a neuroma in continuity that was working, so there was an intact NAP, in fact this was done preoperatively, the patient had function on the standard EMG. In this patient, I placed a nerve stimulator and here is the stimulator placed and the generator in the thigh and this patient has done well with seven year followup. So, different approaches for different pain problems. The last pain problem that I think you should know about for your oral boards is a patient with preganglionic brachial plexus avulsive pain. And here, again, after nonoperative treatment failed, I think one should know something about the DREZ operation, the physiology and the actual technique for doing it. I'd refer you to this excellent monogram with it, but I think this is directed at patients with refractory preganglionic pain, where you'd have pseudo meningoceles and should know a little bit about the surgery. Again, I think the notion that you know this surgery exists is probably the right answer and more than you need to know. With that, I think this tour de force that comes to an end. We talked a bit about the different approaches to peripheral nerve problems. I think you can appreciate my enthusiasm for the subject. I wish you all the best of luck with your exam and with your peripheral nerve practice in life.

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