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Sylvian Fissure Split: Small MCA Aneurysm

January 15, 2016


The Sylvian fissure split is one of the very basic microsurgical procedures that should be mastered early on during the training of our residents. Effective methods to split the fissure can significantly add to the efficiency of the operation. The inside-to-outside technique is often talked about. However, the nuance of technique are seldom reviewed. Let's go ahead and review these basic principles for the inside-to-outside dissection technique and clip ligation of a small MCA aneurysm. This is a 34-year-old female who suffered from an unruptured right-sided MCA aneurysm. This aneurysm was relatively small. However, due to her previous history of subarachnoid hemorrhage from a non-contiguous aneurysm treatment of this small aneurysm was indicated. You can see the size of aneurysm, which is about four millimeters, primarily placed at the level of the bifurcation and somewhat asymmetrically based over one of the M2 trunks. You can also appreciate the relative small length of the M1. Show now into right-sided standard pterional craniotomy. You can see the location of the head. The dural opening. The right sided Sylvian fissure. I use a round arachnoid knife to open the Sylvian cistern along its more generous aspect at the Sylvian point. You can see jeweler forceps are used to gently tear this superficial thick arachnoid bands. This technique adds significant amount of efficiency to the procedure and protects the thin-walled superficial Sylvian veins. Aggressive coagulation is avoided when small bleeding is encountered and irrigation is used to clear the field. I even use this method slightly deeper within the Sylvian fissure. You can see how the superficial thick arachnoid bands are dissected without any injury to the veins. Some of the veins are on tethered, but not necessarily sacrificed along the posterior aspect of the Sylvian fissure split. Next, I use the fine tip, non-stick bipolar forceps to gently dissect the deeper proportion of the Sylvian fissure all the way to the area of that insula. Some of the more superficial arachnoid bands are dissected using micro scissors to avoid peel injury. Here now you can see the inside-to-outside technique. At the most distal aspect of the fissure, I entered deep and identified the insula and the deep arachnoid bands. You can see the M2 branch. Subsequently, I'm going to dissect deep to superficial rather than superficial to deep since the separation between the opercula and the digitations between the temporal and frontal opercula are much more defined along the deeper aspect of the fissure than superficially. Here, you can see the M2 branches remaining deep within the fissure. Early identification of the dissection planes assists with more superficial dissection. Dynamic retraction of the suction device is quite helpful. Here, you can see how the deep to superficial technique or the inside-to-outside technique is employed. Now, the lesser wing of the sphenoid is encountered. Some of the Sylvian veins heading toward the sphenoparietal sinus are preserved. Here, you can see the location of the optic nerve. Generous dissection of the fissure allows gravity retraction to mobilize their frontal lobe. Next, I divert my attention to the area of the aneurysm. The aneurysm is sharply dissected from the surrounding arachnoid bands. So all the branching vessels and perforating ones are identified. Next a fenestrae clip was implanted across the neck of the aneurysm, protecting this smaller branch. Intraoperative ICG angiography demonstrates the desirable result in terms of occlusion of the aneurysm sack and patency of the surrounding vessels. You can see that an atraumatic dissection of the fissure can leave the temporal and frontal opercula very healthy without any significant peel injury. Some of the superficial Sylvian veins are also protected. Postoperative CT angiogram, as well as catheter angiogram in this patient confirms complete exclusion of the aneurysm sack. Thank you.

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