Placement of the Needle within the Foramen Ovale

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This video reviews technical nuances for cannulation of foramen ovale. As well as placement of the balloon within the Gasserian ganglion for compression rhizotomy. I'm going to use the case of a 72 year old male who presented with right-sided V2 and V3 medically refractory trigeminal neuralgia. My preference in terms of using the percutaneous procedure is that if the patient is older than seven years old or medically not amenable to microvascular decompression surgery, my first preference would be balloon compression rhizotomy. And if this procedure is ineffective, I'll proceed with radiofrequency rhizotomy. If ready radiofrequency rhizotomy is ineffective, I consider the use of glycerol rhizotomy. Let's go ahead and review techniques for penetrating foramen ovale. This is the setup in the room. As you can see fluoroscopy guides the surgeon, and we use AP and lateral fluoroscopy as we will review momentarily. The monitor is against the field the view of the surgeon and the assistant is standing behind the surgeon. And other assistant usually handles the head of the patient and ensures that correct trajectory of x-ray is taken. This is lateral fluoroscopy that is typically used. I'll start with marking the area of the skin incision, which is usually two and a half centimeter from the angle of the lip. I use two and a half centimeter as the standard entry point for the needle. Although some operators plan to use two centimeters for a V2 and three centimeter for V3 and vice-versa. So I just use a two and a half centimeter and average of the two for all my needle procedures. After the entry point is identified, we'll proceed and use a small knife to create a stab incision. Set incisions completed. This is only for the needle for the balloon compression rhizotomy, which is typically larger than the needle for radiofrequency rhizotomy or glycerol rhizotomy. you can see that I'm tapping the tip of the needle against the angle of the jaw or the mandible. This is the first landmark that is used on the way to reach foramen ovale. It is also important to know that the needle is approximately heading toward the medial canthus on one of the planes and as well as three and a half centimeter anterior to the internal auditory meatus on the other plane. Here's tapping on the jaw and then coming just medial to that, this is the point where the mucosa gets very thin and therefore it is critical for the surgeon to be very careful while passing the needle in order to avoid violating the mucosa and causing contamination of the needle. You can see my right hand or my non-dominant hand is directing the needle toward again, the medial canthus. And another 0.3 centimeter anterior to the internal auditory meatus. We'll go ahead and get an initial lateral skull x-ray. Before we do that, you can see this as an overlay view of the skull, and how the patient is positioned. You can see that if I had an x-ray vision, this would be the ideal trajectory for me to reach the foramen. And this is what typically I recommend to do as your experience in this procedure increases is that you can imagine where the foramen is just like having x-ray vision, and you can just point your needle to the best you can toward that point and get a lateral skull x-ray. Here you can see the needle is pretty much to the medial canthus or the medial edge of the pupil, and also three and a half centimeter anterior to the internal auditory meatus. Here is how the skull is really overlayed over the head of the patient in the same position, obviously as the patient. And you can see how it would be great with experience to imagine the frame and based on the landmarks of the eye and the internal auditory meatus. After the needle is placed. Here is, again, another view of the internal carotid artery and jugular vein. And another modality for helping you realize the pathway that we're trying to take to reach the foramen without injuring the vascular structures. Here's the initial lateral skull x-ray. You can see that the needle should be pointed at the junction of the petrous bone and the clivus. This area is the ideal point for the tip of the needle to be pointing at. And that's what this needle is doing at this time. Now that in one plane or in the sagittal plane, and we have reached the ideal trajectory, we'll go ahead and use the x-ray and obtain another image parallel to the barrel of the needle. And this allowed us to identify the location of the tip of the needle in relation to foramen ovale. This is a very useful x-ray trajectory. And I'm going to show you an illustration of how this works. Again, you can see, we turn the head contralaterally about 30 degrees, extend the head to make sure the area of the entry is the highest point as much as possible. And then we'll use the extra trajectory parallel essentially, and slightly more medial than the barrel of the needle. This trajectory is essentially parallel through the lumen of the foramen ovale. And therefore we can see the foramen clearly, and know that the tip of the needle is within the foramen. And this x-ray essentially obviates the need to get CSF through the needle to assure the needle placement is accurate. You can see the foramen is clearly demonstrated through that oblique x-ray and here's there clearly the margins of the foramen. And you can see the tip of my needle is just slightly posterior to that. And therefore we'll go ahead and withdraw the needle slightly and just angle the tip of the needle slightly more anteriorly. You can see here, this procedure is completed and you just fall into the foramen. And here you can see the foramen and the needle has already entered it. Typically when the needle enters the foramen, the jaw contracts, and that's another clear indication that the appropriate foramen has been reached. And the reason for contraction of the jaw is irritation of motor roots of the terminal nerve. Now that we have the foramen unequivocally penetrated, we'll go ahead and get another lateral skull x-ray. We can see that we're slightly deep within the foramen. I usually like to be only a few millimeters beyond the skull base. And the reason is for the balloon to achieve a very nice shape within the Gasserian ganglion, rather than being slightly more distal. And then the balloon usually inflates over the petrous ridge and does not reach or cause a nice seal within the cistern of terminal nerve. We'll go ahead and withdrawn a needle slightly. Here you can see another image where the needle has entered the foramen and is just barely into the trigeminal cistern. That is the ideal location for the needle tip. We go ahead and remove this stylet of the needle. You can see clearly CSF is overflowing here. CSF egress is not necessarily needed to assure accurate needle placement as long as lateral and oblique x-rays unequivocally assure that the needle tip is within the foramen ovale. Actually, most of the time, I do not persist on getting CSF. And most of the time I do not get into the CSF cavity. Then the second stylet is used to be able to create a pathway for the balloon. Here's the balloon deflated. You can see that the markings on the catheter guide me how far the needle should go in to make sure the balloon is inflated. We'll go ahead and inflate the balloon. For about 0.8 CC or however much it takes until I can feel a good seal and some gentle pressure resistance against the syringe handle. So it's not necessarily the amount of, or the volume of the contrast that's been injected. Rather, more that pressure and the resistance you're achieving while injecting the contrast. Here is one of the first stages as the balloon is inflating. You can see this as the final product of the balloon. It's slightly overflowing over the petrous ridge. However, you can see just a slight entrance into the V2 foramen, which is ideal. And this is really a considered an ideal shape for the balloon. If the balloon is slightly over, if the needle is too deep or the balloon is inflated too far into the trigeminal cistern, the balloon may overflow over the petrous ridge and not necessarily cause enough compression. After by one and a half minutes of compression, the contrast is completely withdrawn. Additional skull x-rays obtained to make sure all the contrast has been removed and the whole apparatus is subsequently removed. And the procedure is completed with small band-aid over the area of the entry of the needle. Thank you.

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