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Tentorial AVM: Principles of Resection

August 13, 2016


Here's a good example of a tentorial arteriovenous malformation, which describes the advantages of selective preoperative embolization. This is a 41 year old male who presented with history of spontaneous intraventricular hemorrhage. And more specifically, within the fourth ventricle, a large arteriovenous malformation was identified. You can see the very dominant, draining vein touching the surface of the tentorium. Here's the initial angiogram, again, demonstrating this large size of the malformation. Most of the feeding arteries are from the superior cerebellar arteries. The draining vein joins eventually the torcular, and it's one of the hypertrophied tentorial hemispheric veins. Although I usually do not prefer to have the AVMs embolized, for select AVM, such as tentorial AVM. So I do believe embolization is quite useful because the feeding arteries to the AVM are typically on the other side of the AVM, away from the surgeon. The AVM is essentially between the surgeon and feeding arteries. And since early access to these arteries is not possible, their embolization can be quite effective for controlling the bleeding. This patient underwent embolization initially, however, the AVM quickly recanalized, you can see the configuration of the malformation, which appears now more diffuse after the embolization. This is one of the shortcomings of embolizing the large pedicles as the deep white matter feeders, especially in the cerebellum to the AVM can hypertrophy relatively easily. Patient was placed in the lateral position. You can see the generous suboccipital craniotomy while exposing the Ipsilateral transverse sinus. Here's the view under the operative microscope, transverse sinus, cerebellum was carefully released from the tentorium and a large draining vein was exposed. The vein was untethered and followed to the nidus of the malformation. My first goal involves disconnecting as many of the superior cerebellar artery feeders as possible. Here's working on the surface of the cerebellum or the tentorial aspect of the cerebellum. Small cap of the cerebellum over the malformation was then coagulated and removed. Here's the view behind the vein. You can see some of the feeding vessels to the malformation from the SCA. So here's the draining vein, I'm working behind the draining vein to disconnect the feeding arteries. That's an important step during managing these malformations. These feeding vessels were aggressively coagulated and cut. Here's the more poster aspect of the nidus. Again, the draining vein, nidus, feeding arteries. feeding arteries are also being coagulated and cut. I continued to work around the malformation as you can see here, staying outside of the nidus as much as possible to prevent any bleeding from the nidus. Now here's removal of the cap of the cerebellum that I discussed a moment ago. The deep white matter feeder has now become more important. Their control can be quite challenging. We're against outside the nidus as much as possible. The deep white matter feeders harbor a more robust wall away from the nidus. Here's further removal of a small cap of cerebellum, so that the malformation nidus is more clearly visualized. And here's the draining vein, removing a cap of the cerebellum in order to remove the nidus effectively under direct vision. Here's removal of the cap. Here's the nidus, draining vein. Now I can dissect the deep proportion of the malformation much more effectively. Some of the gliosis related to the previous episode of hemorrhage. Ultimately the fourth ventricle will be visible at the depth of our dissection. Here mobilizing the nidus more superiorly. I expect the fourth ventricle to be just about here as you can see, aqueduct, piece of cotton that will be used to cover the fourth ventricle, so bleeding would not drain into the ventricular system during our later phases of dissection. Now disconnecting the more medial wall of the malformation. Some of the SCA feeding vessels may be encountered here as well. Again, I go around the vein while circumferentially disconnecting the SCA feeders to the malformation. Again, portion of the nidus, potentially thrombosed from the initial episode of hemorrhage. Again, here is the nidus more circumferentially isolated, and disconnecting the final, larger SCA branches to the malformation. You can see that the control of the deep SCA branches can be at times challenging while working around a large draining vein. Here again is the surface of the nidus, the more demagnified view of our operative corridor. You're now working more immediately and inferiorly, completing the final stages of AVM nidus disconnection. Now the AVM is mobilized superiorly toward the tentorium and out of our dissection cavity. Here are some of the deeper feeders. Temporal occlusion of the draining vein which was much darker, reveal no further swelling of the malformation. I went ahead and disconnected some of the final peel attachments to the nidus. You can see the vein is quite dark by now. So the vein was coagulated. The vein was cut, and the most posterior attachments to the nidus were also disconnected. The AVM was removed, resection cavity inspected, hemostasis secured. The cavity carefully inspected for any residual nidus. And the fourth ventricle was cleared of any blood. Ample ammonia irrigation used to clear the field. Postoperative angiogram revealed complete exclusion of the malformation, and CT scan revealed no complicating features, and this patient made an excellent recovery. Thank you.

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