December 16, 2015
Let's review tenets for resection of large or giant arteriovenous malformations. This is a 48 year old female who presented with a 6cm right temporoparietal arteriovenous malformation which was previously partially embolized, but not treated further. You can see the location of the malformation on the Chronal images. The embolization materials superiorly can provide some guidance and act as intraoperative navigation compared to preoperative angiography images. Most of the feeding vessels are originating from the distal middle cerebral artery branches. Obviously, this is an important fact to consider during resection of the mass. As the initial steps of operation should focus to the anterior aspect of the mass and disconnection of these vessels. The large draining veins are predominantly within the cortex moving toward a superior sagittal sinus. There's also draining veins going inferiorly toward the deep venous system. Let's look at the angiogram of this malformation to better define the Angio architecture of the malformation as expected on CTA. There are large the feeding vessels from the distal MC branches. There is embolization materials superiorly and the predominant draining vein is moving superiorly toward the superior sagittal sinus. Obviously, this superficial draining vein has to be protected until the end of the operation. The flow within the AVM is relatively quick and therefore this AVM is considered a challenging one in terms of its numerous number of deep feeding vessels and the amount of potential for post operative edema after it's resection. The patient under went a right temporoparietal craniotomy using a horseshoe incision the dura was opened and a currently in fashion based over the base of the temporal fossa, you can see the angio architecture of the malformation, including some of the anterior feeding vessels from the MCA, and also as expected the large draining vein over the surface of the cortex Based on the location of this malformation, I expect most of the feeders to be from the MCA and the PCA, the PCA feeding vessels from P three and P four, almost luckily, along the posterior medial aspect of the malformation. The initial steps of the operation as discussed previously, will focus on disconnection of the mass anteriorly and intra-operative ICG demonstrates again the expected Angio architecture of the feeding vessels and a flow 800 analysis of the ICG. also most likely will demonstrate the feeding vessels that are anteriorly and are supplying most of the flow to the malformation. Here's that flow 800 view with a area marked in red, signifying the majority flow originating from the anterior pole of the malformation. With the available information I started with disconnection of the AVM along its anterior pole. While focusing on finding the dominant large MCA vessels going to the malformation. You can see that the feeding Vessel is found right at the site where it joins to nidus to ensure exclusion of any emphasized vessels, larger feeding vessels are clip ligated and then coagulated on both sides of the clip before they are transected. The clip may be later removed. I use small permanent aneurysm clips rather than the traditional AVM clips as the aneurysm clips are easier to work with inter tension Here's the disconnection of this large MCA feeding vessel. I continue dissection, right that the surface of the nidus here is an emphasized MCA vessel which obviously has to be carefully protected and not inadvertently sacrificed. Here's a large draining vein, I continue the peel phase of dissection right around the borders of the vein. I redirect my attention to the MCA branches. Inferiorly, where a moderate sized vessel is amenable to coagulation and then subsequently transected. Other small MCA branches are coagulated and cut. I continue further dissection inferiorly. Next I disconnect the posterior pole of the tumor from the cortical feeding vessels. Dissection here was relatively easy until, I came in close contact with a large draining vein. I have found that most often there were numerous arterial branches with very thin walls, similar to white matter feeding vessels, close to the large draining veins of AVMs. Their control can be quite challenging. However, one has to be very careful during hemostasis of these feeding vessels in the region of their dominant draining vein to avoid any injury to the vein. patience is necessary to achieve hemostasis in this area, The draining vein looks very healthy. Now the AVM is essentially disconnected mostly anteriorly and posterior, somewhat superiorly here some artifact during coagulation from the embolization material. you can see the difficult bleeding from the white matter feeders here. There was some bleeding from the nidus that I controlled with gentle coagulation. If gentle coagulation is not effective, I usually use a piece of cotton and gentle tamponade to control the bleeding. You can see upon temporary occlusion of the vein the Avion continued to swell. This phenomenon confirms the fact that there are other large feeding vessels that have to be first coagulated and excluded, the bleeding from the nidus at this junction was controlled with a piece of cotton soaked in thrombin aggressive manipulation and coagulation of a nidus should be avoided to decrease the risk of hemodynamic changes prematurely within the malformation. Here is a large feeding vessel from P3 to the malformation along the medial edge of the tentorium that was excluded here is hippocampus the choroid plexus within the right temporal horn. The Plex of feeders to the malformation are coagulated and cut. And the medial temporal structures are carefully protected. Here along the superior aspect of the malformation where the deep white matter feeders can be quite challenging to control. Some oozing has to be tolerated at this stage of the operation. The second temporary clipping of the vein reveals no further swelling of the malformation. Subsequently I placed a clip and coagulate the vein and exclude the vein from the malformation to extract the nidus Remove all the malformation controlled some of the bleeding hemostasis was readily obtained, post resection, ICG, and flow 800 demonstrated it complete exclusion of the malformation without any early draining veins. As you can see here, it's primary arterial feeders, post operative angiogram demonstrated complete exclusion of the malformation without any early AV shunting. There is some large arterial branches that go to the previous area of the AVM. However, there's no venous shunting. This patient recovered from surgery without any complicating features. Thank you.
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