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Brainstem AVMs: Techniques for Resection

December 02, 2015


Hi, my name is Aaron Cohen. This video reviews technical nuances for resection of brain stem arteriovenous malformations. And more specifically, a lateral pontine malformation, just lateral to the 5th cranial nerve on the right side. This is the case of a 52 year old male who presented with subarachnoid hemorrhage around the upper brainstem and was noted to have this lateral pontine malformation with a training vein over the cerebella. The feeders were primarily from the anterior inferior cerebellar artery. Here's a right-sided retromastoid craniotomy. You can see the transversus sigmoid sinuses. The dura was opened along the dural sinuses. Initial dissection of the cerebellopontine angle cisterns exposed two training veins. One over the surface of the cerebellum, which is suspected to be the superior petrosal vein and another larger one slightly deeper, which is most likely the arterialized vein related to the malformation. Further microsurgical dissection allows us to dissect these veins. Next, I obtain an ICG angiogram as well as a FLOW 800 map to better differentiate the identity of the vein here inferiorly versus the vein that was most likely draining the malformation. This information is important as one of these veins has to be sacrificed for me to have enough working space to dissect the malformation. The nidus of the malformation is now more clear against the medial aspect of the cerebellum. You can see the first larger vein, deeper and a more superficial vein. Here's the better anatomy of both of the veins. The ICG angiogram next will determine the rate of flow and the timing of the flow between these two veins. See that the early vein is here and the later vein as suspected was more superficial. The FLOW 800 map confirmed these findings that the inferior vein is most likely unrelated to the aneurism, but is mixing with the arterialized vein. Knowing this information, I sacrificed the inferior vein. In steps, to avoid bleeding. The arachnoid membranes over the nidus of the malformation and its' margins were then dissected open. The feeding vessels to the AVN were carefully skeletonized. Skeletonized and as you can see, the en passage vessel over their medial surface of the cerebellum was carefully protected. Some of the white matter feeders can be quite difficult to control. However, patience and persistence, and following these feeders into the white matter, allows their control using bipolar electrocoagulation. Here's inferior aspect of the malformation, just above the 7th and 8th cranial nerves. This malformation was primarily fed from the branches of the anterior inferior cerebellar artery. And here are these fine feeders that are being carefully exposed over the surface of the brain stem and subsequently transected. The section over the nerves momentarily would show you exactly the location of the 7th and 8th cranial nerves, and how these feeding arteries are actually transversing between the 7th and 8th cranial nerves. Here's the 8th cranial nerve. The first feeder is being coagulated and cut. Usually there is at least two or three additional feeding arteries coming from the anterior inferior cerebellar artery that as you can see, are being found and disconnected. Here's the deeper feeding vessel to the malformation. The surface of the brain stem is carefully protected during bipolar coagulation High magnification assists the surgeon to find these vessels and protect the normal surrounding structures. Here you can see the 7th and 8th cranial nerve complex and how the vessel is actually running between the two cranial nerves. The feeders are being transected carefully to make sure they're completely coagulated. Here are the stumps for both of those feeders. We continue now mobilization of the malformation away from the surface of the brain stem staying right at the nidus, avoiding any injury to the surface of the brain stem just lateral to the 5th cranial nerve. You can see this is a en passage vessel that's being carefully protected. Aggressive coagulation is avoided at the depth of the nidus to avoid any injury to the bystandard vessels. However, the terminal vessels feeding the malformation are being cut, using sharp dissection. Irrigation clears the field. This maneuver avoids aggressive suction over the peel of the brainstem. Now that we have disconnected most of the inferior aspect of the malformation, we disconnect the malformation along its more medial aspect from the brainstem. You can see fixed tractors are avoided and dynamic retraction is more than adequate. Here's the more superior aspect of the malformation that's being dissected. Again, we're just posterior to the root entry zone of the 5th cranial nerve. Here's the tentorium just working below it. Supracerebellar space. Using careful microsurgical techniques, preserving en passage vessels. Now the drain vein was coagulated and cut. The additional vein that was normal is being preserved and the nidus of the malformation is being delivered. Further inspection reveals, no residual nidus. Here again is a branch of the super petrosal sinus, which is normal. We'll go ahead and do another ICG to confirm that this is not an early draining vein. Here is the ICG. You can see that the vein is relatively late compared to the arteries in filling. And postoperative angiogram revealed complete resection of the malformation without complicating features. Thank you.

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