Anterior Pontine AVM: Technical Challenges

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This is a nice video discussing in situ to disconnection technique for a Complex Medial Pontine Arteriovenous Malformation. This is a 26-year-old female who presented with a small and spontaneous pontine hemorrhage and mild left sided upper extremity paresis related to the hemorrhage. CT angiogram demonstrates this very medially located arteriovenous malformation at the lower of the pons with most of the feeding vessels originating from the trunk of the basilar artery. An angiogram was completed which further confirms the vascularity of the malformation from the basilar trunk. The malformation is relatively diffused and has a training vein one then moves more medially and one then moves slightly more laterally and inferiorly. This region was exposed by a right-sided retro sigmoid craniotomy. Patient is in the latter position. Here is the seventh and eighth cranial nerves. Here is the lower cranial nerves. You can see the anterolateral aspect of the brainstem. There is some hypervascularity there. And here is this sixth cranial nerve entering its foramen. Let's go ahead and further inspect this area. The critical step is to identify which feeding vessels are to the malformation and which ones are emphasized vessels to the critical parts of the brainstem. We going to work just above and below the seventh cranial nerve. Here are some corkscrew vessels that most likely feed the malformation. Here are the lower cranial nerves or the arachnoid bands are widely opened. Here you can see a relatively normal appearing vein, and here is what appears an arterialized vein along the anterior aspect of the brainstem. I continue to inspect these vessels. Some of these vessels look somewhat suspicious and corkscrew like. Again, we are below the seventh and eighth cranial nerves. Just medial to the lower cranial nerves. Everything appears to be relatively normal. Here is again, above the seventh and eighth cranial nerves. You can see some hypervascularity. You can see potentially a draining vein moving more medially. Here is the superior petrosal sinus. A FLOW 800 evaluation was performed. Again, this study evaluates the flow within the vessels and it's a quantitative measure of flow. You can see that there is evidence of arterialized vein, just medial to the seventh and eighth cranial nerves as expected. And the super petrosal sinus appears to be normal. A normal vein. However, some of the medial veins are very much arterialized. This is important information for me to confirm the location of the arterialized vein. Working above the seventh and eighth cranial nerves, I temporarily occluded some of the suspicious vessels and evaluated somatosensory and motor evoked potentials for any changes. If no changes were noted, I went ahead and coagulated these corkscrew vessels that were leading more inferiorly and medially toward the malformation. You can see the fine legs or tines of these bipolars that are quite important to allow adequate visualization while working in a very small operative space. Here is another temporary clip just on another vessel below the seventh and eighth cranial nerves. Here is that arterialized vein moving more superiorly and medially. Went ahead and did further dissection to be able to see more medially just around the sixth cranial nerve. The nerve is located here. Sharp dissection is used to look around the anterior aspect of the brainstem. You can see the use of dynamic retraction to work around the brainstem without placing the brainstem at risk of significant retraction injury. I suspect the nidus of the malformation would be located here. And the basilar artery should be just medial to the nidus. Here are some of the corkscrew vessels toward the malformation. These are most likely from the basilar trunk. Here is the nidus of the malformation. I'm going to use the epipial or insight to resection or disconnection technique. In other words, I just disconnect and coagulate the surface vessels and do not pursue the malformation into the brainstem. Here is another corkscrew vessel that has been coagulated and cut. Here is an less magnified view of the operative cavity. Periodic irrigation is used to keep the operative field clear. We will go ahead and continue our dissection. Here again, you can see the arterialized vein on the surface of the brainstem. We are just below the seventh and eighth cranial nerves. Of note, I use a piece of gel foam soaked in papaverine to cover the eighth cranial nerve and protect it during my dissection from the intense light of microscope and the risk of thermal injury from this intense light. Continue working along the anterior aspect of the brainstem, opening all the arachnoid bands. My goal is, again, to identify the nidus and the basilar artery just medial to it. Here is a flow study again demonstrating the arterialized vein. Basilar artery would be located more medially. Here is the nidus of the malformation. This is good information for me to be able to conclusively confirm the location of a nidus and its feeding vessels and the draining vein. Next, we will go ahead and continue our medial dissection some of the perforating vessels from the basilar artery. Here is the basilar artery finally identified. Now, I'm going to go ahead and skeletonize and disconnect these feeding vessels. Ultimately, the basilar artery should be skeletonize on this side, so all the feeding vessels to the malformation are disconnected. Here are the feeding vessels from the basilar trunk. And the basilar artery, the feeding vessels, which are being coagulated and cut. The depth of the operative field is quite long. Very fine tipped bipolar forceps are necessary. Again, continuing to skeletonize and disconnect these feeding vessels. The irrigating bipolars are quite effective. Here is the basilar artery. Feeding vessels are being disconnected. Here is another feeding vessel to the malformation. Here is the stump of the feeding vessel. That is being well coagulated to avoid delayed bleeding. I think, this is one of the last ones. Here, you can see the two feeding arteries from the basilar trunk that are very much apparent. I don't see any other feeding vessels to the malformation as I look further cranially along the basilar artery. Some of the feeding vessels on the surface of the brainstem are also coagulated and ultimately, the draining vein is also coagulated. All the dissection is confined to the epipial space. Here is working above the seventh and eighth cranial nerves. This is one of the draining veins that will ultimately be coagulated here. You can see that these draining veins are becoming less and less arterialized based on flow evaluation. So, they are ready to be also coagulated and cut after which hemostasis was secured. Postoperative angiogram demonstrated complete disconnection of the malformation. Again, you can see these stumps of feeding vessels that are apparent on the basilar trunk. This patient made a nice recovery. She had some temporary worsening of her hearing and slight facial weakness, both of which resolved under three months follow-up. Thank you.

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