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Posterior Fossa Exploratory Surgery for Geniculate Neuralgia

Aaron Cohen-Gadol, M.D.

October 22, 2014

Transcript

- Hello, ladies and gentlemen. Thank you for joining us for another session on the AANS operative grand rounds. The following session will be discussion regarding surgical management of geniculate neuralgia or primary otalgia or neuralgia due to nervus intermedius. This is a rare and difficult disorder to diagnose. We'll discuss today Some of the technical nuances related to exploratory posterior fossa surgery for transection of nervus intermedius. Thank you.

- Bill, thanks again for joining us. This is a very rare disorder, thanks God, geniculate neuralgia or primary otalgia or severe ear pain or ear canal pain. It's also called nervus intermedius neuralgia because originates or the pain is supposed to come more commonly from nervus intermedius which is located between the seven and eighth cranial nerve in the cisterns of the seven and eighth nerves. This is extremely rare, and the diagnosis absolutely critical because so many different pathologies can overlap in terms of creating ear pain. However, for patients who are absolutely miserable with the pain and are often suicidal, this procedure that is technically challenging actually can be very much satisfying. It happens maybe once or twice a year for me and, you know, I treat about 200 trigeminal neuralgia patients who require surgery with MBDs a year. And I'm sure for you it's as rare that doing the posterior fossa exploratory surgery for severe ear pain or primary otalgia is rare And the diagnosis has to be very carefully considered. What are your pearls in terms of the diagnosis and treatment?

- So as you mentioned, Aaron, it's a very difficult diagnosis to make with absolute certainty because there's a lot of overlap with the other pain syndromes. Trigeminal, and obviously glossopharyngeal. You really wanna make sure you're not missing glossopharyngeal neuralgia. And I had the patient seen by otologist and head neck specialists. We do a complete radiographic workup, both CT and MRI, to look for any pathology at all that could be causing the ear pain prior to considering this. And also obviously they need to be medically refractory. So ultimately it's an extremely rare disease that we only see a few cases compared to the the vast number of trigeminals and less across glossopharyngeal neuralgias we see.

- Thank you. And this is briefly the discussion before we proceed, none of which really interferes with the presentation. So let's define geniculate neuralgia pretty briefly. It's an involuntary intermittent or potentially partly constant neuralgic pain deep within the ear canal. The pain may radiate to mastoid or occipital regions of the face. But again, primarily the pain is in the ear canal. The nerves that innervate the inner canal or the surrounding areas are 5, 9, 10, and most importantly, nervus intermedius that is responsible for taste and lacrimation. Is this another neuralgia neurovascular conflict syndrome, such as trigeminal neuralgia and hemi facial spasm maybe. But again, the verdict is out there because it is such a rare disorder and treatment options are mostly anecdotal. The series are very small and again the surgical treatment has to be very, very cautiously offered. Here is a patient's interview that would illustrate what typically geniculate neuralgia can be described by the patient. You can please pay attention to details of his description, as you will find out the nuances of diagnosis are absolutely the most critical factor in good outcomes in this disorder. Can you please tell us about your pain?

- The pain I have is very intense. Worst pain in my life, 10 out of 10 on the pain scale. It would feel like I was being stabbed in the head with an ice prick or sharp object, right at the ear canal. Would come and go. The pain would be intense for a few seconds, go away, come back within a minute or two. I would have periods of remission where I wouldn't have any symptoms at all. And then for a day or two, I would feel like I was being stabbed a hundred times a day. It was terrible. And the wind from the air conditioning turning on, I could feel the light breeze from the air conditioner on my ear, and that would trigger a pain episode. The point where I wouldn't try to avoid being around places where air conditioning or windows were open, just to try to prevent being around a breeze.

- Okay. Can you tell us where exactly the pain was again?

- The pain was right near the ear canal. It felt like I was either being stabbed in the ear deeply or deeply through the area directly around the opening of the ear canal.

- Thank you.

- Note that we have listened to that patient's interview. Let's talk about some additional basic information. And again, it's extremely rare. it's often misdiagnosed. And again, the neurologic character of being, you know, I like to recall having cutaneous features and response to neuropathic medications such as tegretol is important. It is again, the triggers are tactile stimulation within the ear canal, coughing, yawning, swallowing, and taking a shower as the water gets into the ear often creates a severe electrical shock. What has been your nuances of diagnosis in terms of this disorder of Bill?

- So I agree with you. I think you've nicely described the basic clinical features to this. I think one of the important things is to differentiate it obviously from glossopharyngeal neuralgia because they can present primarily with ear pain as well. And to differentiate those two. And I like to have a laryngologist and head neck surgeons look at the patient with me. And we often do the anesthetic test in the posterior pharynx to rule out glossopharyngeal neuralgia before we consider geniculate neuralgia.

- Okay. Okay. Thank you. And as you very well mentioned, we need a CT MRI of the brain and the ear, and a very thorough ENT evaluation, a dental evaluation or other possible evaluations. Strictly exclude head and neck pathologies if there's burning pain around the ear and ear canal it could be part of Ramsay hunt syndrome that is herpes infection. And a 10% cocaine solution injection into posterior pharynx if the result causes pain relief for a couple of hours, that is consistent with diagnosis of glossopharyngeal neuralgia as glossopharyngeal neuralgia may have only ear pain as it's presenting symptom. And if that's the case during exploratory surgery, you wanna pay special attention to the lower cranial nerves and proceed with surgery as you are focused on glossopharyngeal neuralgia. At times, xylocaine solution injection into the ear canal may cause some relief and that can be consistent with diagnosis of genicular neuralgia. But again, these are not very perfect pathognomonic diagnostic features for genicular neuralgia. The correct diagnosis is most important that neuralgic pain of shooting electrical pain upon touching the ear canal, swallowing, chewing, water into the ear or the wind going through the ear canal, it causes that shooting pain that's critical. Many conditions can cause ear and face pain. A typical facial pain, primary pathology of the ear, oral cavity, head and neck pathology, Temporomandibular joint disease, probably one of the most common causes of ear pain and besides, common cause of chronic ear pain, let's put it that way. Probably, acute ear pain is the infection and otitis media externa. And again, carcinoma of the nasal pharynx very often can present as ear pain and you don't wanna miss that on time. Again, what are the treatment options? Carbamazepine. And if the pain is extremely disabling and the patient comes and says, listen, I have typical neuralgic pain and you can definitely verify that, and the pain is so excruciating that the patient can be suicidal at times. I think a consideration in this situation of surgical treatment would be reasonable. Any thoughts there Bill?

- No, I think that's been nicely described. And we would do exactly that workup, both trying to quell the pain with either posterior fossa injection of cocaine in that case or the inter-operative or intra-ear xylocaine as well, is a good, useful test.

- Thank you. And here we are. What are the surgical treatment options? Posterior fossa exploratory surgery exploring the seven, I'm sorry, the five, seven and eighth complex as well as nine and 10 cranial nerve complexes along the brainstem. If there is an evidence of vascular compression along any of these nerves, we go ahead and mobilize and transposition the nerve and place a Teflon patch. We will consistently proceed and section the nervus intermedius, which can be technically challenging to identify between the seventh and eighth cranial nerves and cut the nerve and potentially consider sectioning the ninth nerve and upper rootlets of 10, if a suspicion of glossopharyngeal neuralgia is present. What are your thoughts in terms of surgical options, Bill?

- Yes. I mean, we would perform a lower cranial exploration in such a case and look for vascular compression of either seven and eight or nine, 10, 11, and plan to go ahead. And if there was vascular compression of nine and 10, we would do a microvascular decompression. And if there was no conflict at all with seven and eight, we may just leave it at the first operation. And then secondly, look at nervus intermedius and section that.

- Okay. So would you, if you don't find the vascular compression at the primary first operation, would you consider finding the nervus intermedius and cutting it?

- Yeah. If it was easy to identify, we would go ahead and cut that. I think that's a reasonable option.

- Thank you. Other options that have been described in the literature include sectioning of the geniculate ganglia or chorda tympani through a middle fossa approach, but I think those surgical options are much more invasive and really have to be very, very cautiously offered to the patient, because of the morbidities that could be associated with a more extensive middle fossa exploratory surgery in addition to a posterior fossa exploratory surgery. Also, imaging is important to rule out a structural pathology. High resolution MRIs offer negative, again, the surgical exploration is very cautiously offered in terms of in the face of adequate diagnosis. So what is the surgical anatomy of nervus intermedius? There is three pitted supple segments to this nerve described by Al Hopkin The proximal segment is closely related to the seventh nerve at the root exit zone of the seventh nerve, along the brain stem. The intermediate segment, which is the free segment between the seventh and eighth cranial nerves, just a little bit distal to the proximal segment is the most free piece that floats easily between the two segments. Not easily in terms of finding it surgically, but at least it's somewhat separate and then it's most accessible for the surgeon to identify. So, in other words, if you can dissect over the seven and eighth cranial nerves from the vestibular nerves, the nerve is most likely between the seven and eighth and along the middle segment of the cisternal portion of the seven and eighth complex. And the distal segment of the nervus intermedius often is incorporated into the seventh nerve and is not dissectable without morbidity. What is most important is that we have to be very careful to dissect this nerve from the eighth nerve as the long-term consequences of medic refractory vertigo can be very disabling. And therefore, not much aggressive resection should be performed. There's usually two to four fascicles for the nervus intermedius and 20% of the patients may not have a distinct nervous intermedius despite adequate inspection, even into intermediate segments. Any thoughts regarding the surgical anatomy, Bill?

- Yeah, I think the key is to really make sure that you can identify it properly because it's a morbid operation. If you either end up injuring the seventh or some of the distributor components. And so we only section it if we're sure that we can identify it well, and it's obvious.

- Okay. Thank you. And again, inter operative monitoring the seventh and eighth cranial nerves is important. Do you monitor anything else, Bill?

- Well, we would do EMG for seven as well in a case such as this.

- Okay. So you wanna make sure as you're dissecting, you are not gonna overstimulate or injure the nerve.

- Correct. Also we can use it to help differentiate the nervus intermedius from the seven main branches of them.

- Okay. Thank you. And then here is an MRI of a patient with primary otalgia, and as you can see, there is this loop of the vessel potentially along the root exit zone of the seventh cranial nerve. This is another image again, showing potentially a vessel in the region. And here is, interestingly Bill, we found in one of our patients that we wanna report is this patient had a very classic primary otalgia and had the stimulation evidence of hyperactivity in functional MRI in his brain stem along the trigeminal spinothalamic tracts. And so this may be something in the future that people can look into in terms of identifying pain syndrome, specifically affecting the spinothalamic and trigeminal thalamic tracts. Nothing that, again, pathognomonic the clinical diagnosis is more important.

- It would be nice to have an objective correlate though.

- Correct. As you can see, there's some hyperactivity you can see on the trigeminal spinothalamic sensory tract. And again, the position of this operation is very similar to trigeminal neuralgia and neurocranial nerve decompressions, microvascular decompressions, we're not going through the details right now. I would like to ask our viewers to refer to the previous presentation on glossopharyngeal neuralgia that has been recorded again by Dr. Phil Caldwell, demonstrating his neurolysis for evaluation. And, I'm sorry, for performance of posterior fossa surgery. Here is an illustration of examining the nerve after the cerebellum has maybe been retracted medially. And I tried to expose and identify the root exit zone, I'm sorry, root entry zone on the trigeminal nerve. And if there is a vein and not necessarily compressive, we leave that alone. And then next we attract our attention to the nerves seven and eighth cranial complex, where we look first above the nerve between the seven and eighth nerve. And again, the seventh nerve is more grayish in color and is anterior It starts inferiorly and moves superiorly and anteriorly. The eighth cranial nerve, also known as the vestibulocochlear nerve are more whitish and more posterior and both posterior in origin and posteriorly sort of path, therefore pathway is more posterior. And after we look at the nerve above them, we attract, if we can't find the nervus intermedius, we try to go more inferior and usually find the fascicles of the nervus intermedius and prepare them for transection. Often there is a vessel between the seventh and eighth cranial nerve complex as well, making the dissection easier. What are your nuances of technique for identifying the nervus intermedius, Bill?

- So in this case, you wanna look both inferiorly and superiorly and try to separate out seven and eight and see what the root entry zone of the brainstem, and then follow up between them and look in the cisternal segment to see if you can find nervus intermedius in between the two. And I think it's critically important in this case to try and really mobilize and look from inferiorly, but from superiorly, try to, you know, reduce the amount of manipulation of the eighth nerve, as much as possible, because this is where the morbidity comes in with the operation is manipulating the eighth nerve trunk when you're trying to look for seven, the nervus intermedius between seven and eight.

- Right. In other words, what you're mentioning, Bill is that you don't want a patient who wakes up still having horrible pain, and now can't walk anymore either. I think that that's essentially the worst of both worlds. Unacceptable outcome. And here it is holding the nervus intermedius with the hand dissector and cutting the nervus intermedius again mobilizing the arterial routes along the brainstem, along this ninth and 10th cranial nerves. And again, decompressing any vessels around as seven and eighth cranial nerves as well. And here is really me. I'm trying to look around the root entry zone of the fifth nerve inter-operative photo. Again, looking inferiorly, finding the nervus intermedius with the dissector. Again, this is the seventh and eighth cranial nerve. And again, after that, the cut, the nervous cut, and we look at the root exit zone of the facial nerve and between the seventh and the eighth cranial nerve. And there's usually a vessel or a vein and artery running between the two. And any additional vessels can be mobilized. Again, you can see how much, with adequate microsurgical techniques, you can dissect the vestibulocochlear nerve from the facial nerve and be able to look in between without causing significant morbidity. Any thoughts here, Bill?

- Yeah, I think again, just like we discussed in the glossopharyngeal neuralgic case is that you need to look right at the brainstem because if you just focus on the cisternal segment, you really wanna look back at the brainstem, see the root entry zone of both those nerves and make sure there's no conflict at that level.

- Thank you Bill. And here it is, just like you mentioned, Bill, looking at the brainstem, mobilizing the arteries, placing Teflon patch to assure there is no evidence of compression, either at the seventh and eighth complex or the lower cranial nerves. And again, for the exposures, please refer to the trigeminal neuralgia or hemifacial spasm as well as glossopharyngeal neuralgia sessions for craniotomy and exposures. Let's go ahead and look at some of our videos. Short videos that would again, illustrate some of the basic standards for management of genicular neuralgia. Here as you can see that basic exposure or posterior fossa approach. The lower end of the transfer sinus is not visible as it's not necessary to expose the posteromedial aspect of the sigmoid sinus is exposed. Here is gently retracting the cerebellum and opening the ocular membranes. The bars are perfectly monitored to ensure that the gentle medial retraction of the cerebral hemisphere is not interfering with the eighth cranial nerve. Here is looking at the root entry zone of the fifth nerve. And again, nothing convincing is evident. Go ahead, Bill interrupt me at any time you can.

- Yeah. So we're looking for any significant conflict. You've got an artery there by seven and eight.

- And I think that's more of a vein. The artery is more superficial, but again, we look superiorly, I know you don't have the 3D view here to adequately see to the instances, unfortunately. And here it is sort of pulling on the nerve with a gentle dissector you sort of go round ' between the two and find the fascicles of the nervus intermedius, and then hold it with your suction. Go ahead and cut it with your micro scissors. And again, here is those vascular loops that you very well mentioned, Bill. You have to identify them, mobilize them, and carefully place the implant. Go ahead.

- There's one point that when we cut vessels, I try to cut a segment of the vessel or cut a segment of the nerve and remove it just to avoid any potential for reanastomosis of the nerves. So when we kind of glossopharyngeal nerve or nervus intermedius, we cut a section of the nerve.

- Okay. That's a grand nuance. He already is between the seven and eighth cranial nerve. You can see, got to be very gentle, retracting these two vessels and create this space between them and putting the Teflon implant to mobilize the arterial loop from the lower cranial nerves. Would you have done anything different here Bill?

- No. I think that's exactly what I would have done. I would have sectioned the nervus intermedius, see if we can find it so easily and then decompress the vessel loop as well.

- Okay. And I think again, further placement of the Teflon implant to assure adequate mobilization. Go ahead, Bill.

- Yeah. The one point that we like to do is if we can mobilize the loop such as that, we'll try to sling the loop away and we'll... It so hard to do in this situation because you don't have a lot of working room between seven and eight and nine, 10, 11, but we'll try to mobilize the artery away and sling it away, and hold it. And we'll stitch it, or sometimes fibrin glue the Teflon sling to hold the artery away.

- And you would stitch it to the dura of the peach Rispoli, is that correct?

- Correct. The pitches or the clivus depending on where you have to put the sling

- Okay. And you think that could potentially have a better outcome than just putting the Teflon patch as it is in this case?

- Yes. I don't know. But I prefer, if I can, to leave absolutely nothing touching the root entry zone or the nerves, as my primary option. If I feel I can't achieve that, then we'll do the intravasation of Teflon as you've nicely demonstrated here.

- All right. This is another patient, Bill. Again, left sided approach. Had primarily primary otalgia and look during this exposure, how the ninth nerve is being compressed and sort of conflicted with every pulsation of the vascular loop. And in this situation, we looked at the seven and eighth complex here, and absolutely no vascular conflict was evident. We did look for any branches of nervus intermedius or its fascicles and nothing was evident. And we did not wanna place the patient at an increased risk of post operative vertigo, and eighth nerve dysfunction. And so after adequate inspection around the seven and eighth nerve, at seven and eight complex, we went ahead and placed the Teflon patch between the ninth nerve and mobilized the nerve, and ultimately cut the ninth nerve. And the patient did very well. And it really shows again, that glossopharyngeal neuralgia can have very much overlaps with the genicular neuralgia and the ninth nerve has to carefully inspect it. This is a branch of labyrinthine artery, that went in between the seven and eight and was decompressed also. But again, this vessel has to be carefully preserved. I think the results can be very much variable. The short-term results are good up to 75% of patients with primary otalgia. Unfortunately, the long-term outcome is only 30% good based on the report of Fidel Janetta and others. The complications can be serious. The vertigo, hearing loss, and decreased taste, and lacrimation. Again, this is an operation that is nowhere comparable to microvascular decompression surgery for the fifth nerve, for the ninth and 10th nerve, and for the seventh nerve for a facial spasm and therefore judicious patient selection is so critical. And Bill, any closing statements, please?

- Yeah, I think you summed it up nicely, Aaron. I think that this is a less gratifying operation ear pain than glossopharyngeal pain classic throat or of course, trigeminal pain, which is usually a home run in very well selected patients. So we do this very occasionally, but only willing well-selected patients. Thank you very much.

- Bill, thanks again, as always for your expertise. We really, really appreciate your time. Thank you.

- Thank you.

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