June 10, 2015
I use the modified Orbitozygomatic Osteotomy very infrequently and very selectively. In fact, I use this craniotomy for high ridding parasellar and other interpeduncular lesions where significant frontal retraction may be necessary to reach the superior pole of the tumor via the standard pterional craniotomy. As previously discussed, I do modify my regular pterianal craniotomy with drilling of the orbital roof to avoid routine use of Orbitozygomatic Osteotomy. Let's go ahead and describe the techniques for the one piece modified frontozygomatic osteotomy or craniotomy. This is a 40 year old male who presented with a large third ventricular craniopharyngioma. This tumor was primarily within the third ventricle without any significant suprasellar extension. It's been my routine to approach almost all craniopharyngiomas, no matter how far there are within the third ventricle, via the endoscopic transnasal route. Today, I would approach this tumor via the transnasal route, however, this case was managed a few years ago, and at the time we used the orbitozygomatic craniotomy, for resection of large search masses primarily within third ventricle. The frontozygomatic craniotomy provides an expanded inferior to superior operative trajectory to reach the superior pole of the tumor via the trans-laminal terminalis approach. This patient underwent a left sided one piece Orbitozygomtic craniotomy. You can see the minimal amount of head turned toward the right side. Standard curvilinear incision was used. I do use lumbar drain quite liberally to decompress the dural sac and protecting to dual contents, including the dura itself during the osteotomy. Following completion of the scalp incision, the scalp is reflected in a separate layer and a subfascial technique is used to elevate the fat pad. The frontal process of zygoma and the keyhole is clearly palpated using the subfascial technique. The superficial layer of the temporalis fascia, as well as the fat pad, including the deep player the superficial temporal fascia elevating one layer. As you can see a piece of pericranium was also elevated. If necessary, in case the frontal sinus is inadvertently violated, use the subfascial technique. You can see, the monopolar corridor is used parallel to the routes of the frontalis nerve until the muscle is encountered. Once the temporalis muscle is encountered, the superficial and deep layers of temporalis fascia reflected along with fat pad. As we all know, the frontalis nerve is primarily within this superficial layer of the temporalis fascia and not within the fat pad. Transection of the fat pad or the fascias parallel to the superior temporal line should be avoided, as the route of the frontalis nerve, again is essentially parallel to the direction of the frontal process of zygoma. Here now the frontal process zygoma is being exposed via sub periosteal fashion. The pericranium joins the periorbital at the rim of the orbit. You can see the periorbital is carefully dissected from the anterior aspect of the orbital roof. Supraorbital nerve should also be identified and protected and may have to be mobilized out of its groove. A cuff of fascia and muscle are left behind at the level of the superior temple line for later closure of the temporalis muscle. The temporalis muscles is then reflected inferiorly and slightly posteriorly, in contrast to irregular pterional craniotomy where the muscle is reflected along with a skull flap anteriorly. Here's further dissection of that temporalis muscle. Obviously you don't want to mess with the muscle to interfere with a subfrontal trajectory. You can see the keyhole is generously exposed. Fishhooks are used to mobilize the muscle out of our working zone. Further mobilization inferiorly maybe necessary. In front two zygomatic suture is found and a few millimeters above and few millimeters posterior to the zygomatic suture is the appropriate place for placement of their keyhole. Again the keyhole should be placed with a drill at 45 degree angle to the surface of the skull. A bare hole should not be created with the drill perpendicular to the skull bone as only the dura of the frontal lobe will be low exposed. Here you can see the periorbita was initially exposed in the area at the tip of my arrow. Next, the roof of the orbit is skeletonized after the dura of the frontal lobe is also identified. Kerosene ranguers are used to further skeletonize and delineate the exact location of the orbital roof. Now more of the frontal dura is being exposed, accurate placement of the keyhole is essential for efficient and accurate completion of the one piece orbitozygomaatic osteotomy. Here's the identification of their frontal dura. CSF drainage through the lumbar drain assists with mobilization of the dura and its protection. Here's further removal of the bone in this area. The roof of the orbit is apparent. The dura may be dissected away from the inner aspect of the calvarium as much as possible. And other bare hole is placed along the posterior aspect of our bonny exposure just inferior to the square temple line. This bare hole allows generous stripping away of the dura from the inner surface of the scalp bone. The dissection here is unobstructed by the temporalis muscle. And we're just about ready to start our bonny cuts and osteotomies. The first bonny cut is from the poster bare hole all the way to the orbital rim. The frontal sinus is avoided as much as possible as long as the exposure is not compromised. I turn the drill 180 degrees and remove the footplate. Now through this slightly expanded bonny removal, an osteotomy of orbital rim maybe accomplished. Before doing so, let's go ahead and complete our temporal aspect of the craniotomy. I'll stay us inferiorly as possible, and advance my footplate and drill, the B1 until further progress is halted by the lateral aspect of the sphenoid wing in the area of the pterion. Next, the bone over the latter aspect of the sphenoid wing is drilled away using only the B1. Most of the maneuvers so far are pretty typical of a pterional craniotomy. Bonny removal extended to the area of the keyhole. The next osteotomy is across the frontal process of zygoma. Special can protect the periorbital and the interorbital contents. This osteotomy joins the other osteotomies along the latter aspect of the sphenoid wing. Next, an osteotomies completed along the rim of the orbit. This maneuver is quite important for completion of the one piece osteotomy, and this one should be thoroughly disconnected. Next, the periorbital is further dissected away from the roof of the orbit. Similar maneuvers completed for the frontal dura. Two pieces of cotton patties are inserted to protect the periorbital and the frontal dura during disconnection of the roof of the orbit using a small osteotome. The osteotome is used used to disconnect and fracture the roof orbit, and the direction of the osteotome toward the cut or the osteotomy at the level of the orbital rim. Here's the direction of the osteotome toward the cut at the orbital rim. Next, the orbital roof is gently fractured. If significant resistance is encountered, it's best to complete the orbital rim and orbital roof osteotomies. Further, aggressive elevation of the bone flap should be avoided as the fracture along the orbital roof can extend to the optic canal. This is especially true for meniangiomas along the lateral and medial aspect of sphenoid wing. The frontal sinus was encountered. In this case, the mucosal of which was thoroughly removed and a piece of temporalis muscle was placed to plug the frontal sinus. Piece of temporary fascia was also used to fill the defect and a piece of bone wax sealed off the opening into the frontal sinus. Next, the remainder of the orbital roof is further thinned out, So that the exposure along the subfrontal area is unobstructed by the residual orbital roof. The latter aspect of the sphenoid wing is also drilled away all the way to the area of the superior orbital fissure. The dura is next open in a curvilinear fashion and retention sutures are placed at the route of the dura along the sub frontal area. So the traction on the sutures will gently depress the orbit and provide an expanded inferior to superior trajectory toward the parasellar area. Again, you can see the location of the sutures and their attraction to gently depress the periorbital and interorbital contents. Here's the final result, Immaculate hemostasis is obtained along the epidural space. You can see the removal of the part of the orbital rim and frontal process of zygoma provides a very nice inferior to superior trajectory toward the sub frontal area, without significant retraction of the frontal lobe. If the optic foramen is effected, especially in the case of meningiomas, an extradural clinoidectomy may be accomplished for early decompression of the nerve before it is manipulated for tumor resection. Again, I use the orbitozygomatic osteotomy and specifically the one piece variation of it very sparingly. I believe the extended pterional craniotomy with some drilling of the orbital roof and the lateral aspect of the sphenoid wing, provides a number of advantages, somewhat similar to the orbitozygomatic craniotomy. Thank you.
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