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Pterional Craniotomy: Subfascial Technique

January 15, 2016

Transcript

The terms of interfacial versus subfascial technique for reflection of the temporalis muscle and protection of the frontalis nerve. During performance of Pterional and Orbitozygomatic Craniotomies can be quite confusing. Let's go ahead and define these terms effectively and discuss their indications. First let's review the anatomy of the frontalis nerve. Obviously we're on the left side of the head. You can see the eye of the cadaver there for orientation. The frontalis nerve is essentially parallel to the post area edge of the frontal process of zygoma. You can see that the nerve is housed within the superficial layer of the temporalis fascia. Also, you can see that the edge of the fat pad, which is just below the superficial layer of the temporal fascia is way posterior. Than were the nerve is. The nerve is essentially a centimeter to a centimeter and a half, posterior to the age of the front process of zygoma. These anatomical landmarks are quite useful. You can also see that different frontalis nerve continues just along the edges of the frontal process of zygoma to enter the muscle. Therefore during the reflection of the muscle or reflection of the fat pad, transection and distraction should be avoided as it will lead to paralysis and permanent injury to the nerve. Let's go ahead and review some of the other basic concepts here. You can see that in this cadaver, the scalp has been reflected all the way to the level of the fat pad. There are four layers to the fat pad and adjacent fascia layers. The first one is state superficial layer of the temporalis fascia. Then its the fat pad itself or the interfacial fat pad. Then its the deep layer of the temporalis fascia. And then it's temporal muscle itself. Again, one has to remember that the frontalis nerve is not housed within the fat pad, but rather within this superficial layer of temporalis fascia which is just above the fat pad. Here is a more magnified view of this anatomical landmark. Again, the superficial layer of the temporalis fascia, the interfacial fat pad, the deep layer of the temporalis fascia and the temporary muscle itself. Cutting perpendicular to the front process of zygoma will lead to transection of the nerves. As you can see here, dissection should be carried parallel and just posterior to the frontalis branches which are about a centimeter post area to the poster edge of the frontalis process. Here is another dissection. You can see that the deep layer of the temporalis fascia is identified, and this is the interfacial technique or the fat pad and the superficial temporalis fascia have been reflected in one layer. Let's go ahead and review the details of the interfacia technique one more time. You can see that scalp has been reflected anteriorly, the superficial temporalis fascia and interfacial fat pad have been reflected in one layer. And the deep fascia remains intact and separated in a separate layer. I do not use this technique. I use the subfascial technique that I'll review in a moment. I believe that the subfascial technique will protect the front house branches more effectively. Again, the deep layer of the temporalis fascia is left alone and reflected with the muscle in a separate layer. The planes of dissection along the superior temporal line are important and should not transect the routes of the frontalis branches. Again, after the superficial temporal fascia and the fat pad have been reflected the keyhole and the frontal process of the zygoma are generously exposed, and the temporalis muscle is reflected inferiorly. These maneuvers are all generous exposure of the keyhole and the area of that pterion. Let's now review the subfascial technique, which is my preferred approach. You can see that the scalp has been reflected along with the superficial temporalis fascia, the interfacial fat pad along the deep layer of the temporalis fascia. all in one layer. Here is a magnified view again, The fat pad, the superficial layer and the deep layer of temporalis fascia reflected all in one layer in the temporalis muscle and the posterior aspect of the deep temporalis fascia are reflected inferiorally in a separate layer. Let's go ahead and review this sub fascial technique during an operation. The incision of arterial craniotomy, which is curvilinear is being completed. I use a wide spatula and separate the scalp from the fascia of the temporalis muscle. I use the belly of the knife to conduct the dissection parallel to the surface of the skin. You can see that the wide spatula quite effective to efficiently complete the dissection. Using the wide spatula actually can effectively protect the superficial temporal artery or at least one of its branches. In this case, the pridal branch had to be sacrificed, but the front top ranch remains intact. After hemostasis is obtained on both sides of the scalp edges. You can see again, the final branches of the- as they are protected. The dissection around the root of the estate is conducted using Metzenbaum scissors. Here's another branch of that pridal artery. The belly of their knife is used to mobilize the scalp anteriorly and identify the fat pad the posterior edge of which is not apparent. I palpate the frontal process od zygoma and the keyhole and their junction. Next the monopolar cautery is used to conduct the subfascial dissection. You can see the fat pad is entered. The temporalis muscle is exposed again, That trajectory of dissection is parallel to the frontal process of zygoma. Here's the spear temporal line. Now the deep temporalis fascia and the fat pad, and is superficial temporalis fascia are reflected in one layer. Dissection is continued parallel to the frontal process of zygoma and not perpendicular to it. Obviously you don't want to transect the frontal house branches here either. cuff is left behind along the superior temporal line for easy closure and re-approximation or the muscle. At the time of the closure. You can see that post area dis-articulation of the muscle. Now the fat pad and a deep fascia is mobilized anteriorly until the frontal process of zygoma is identified. The muscle is reflected inferiorly and not interiorly as in the case of techniques where the entire myocutaneous flap is reflected in one layer with the scalp. The temporalis muscle can be elevated without the use of monopolar cautery to avoid devascularization of the subprime ostial layer of the muscle which nourishes the temporalis muscle fish hooks are used. The area of the keyhole is generously exposed. Obviously the muscle can reflect it more inferiorly if necessary. So an orbital psychosomatic craniotomy can elevate it. Obviously the frontal process of zygoma and the orbital rim will be exposed for such a maneuver. Thank you.

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