December 17, 2015
This detailed video reviews, tenants for performance of a pterional craniotomy for resection of medial sphenoid wing meningoma. This is a 65 year old female who presented with confusion and mild speech dysfunction. And an MRI evaluation was noted to have a left sided medial sphenoid wing mass, which is homogeneously enhancing with evidence of hyperostosis at the area of interior clinoid process. This mass is most consistent with a meningioma, with associated moderate mode of edema. You can again appreciate on the coronal images, this mass that is centered over the anterior clinoid process. She've subsequently underwent, a left frontal temporal craniotomy. The head is fixed in the skull clamp, the standard atrial incision is marked. Let's review the details here briefly, the turn of the head depends on the location of the mass relative to the midline. This mass is relatively lateral, therefore about 30 to 45 degrees is very appropriate for reaching the mass. The keyhole is marked, as you can see here. The beginning and the end of the incision can be connected with an imaginary line. This imaginary line should be within a centimeter of the keyhole. If such a principle is obeyed by this scalp incision and reflection of the scar flap would alow adequate exposure of the keyhole. More limited incisions can prevent adequate exposure of the keyhole and a reflection of the temporalis muscle to adequately identify the area of the pterion. Let's go ahead and now review techniques for performance of the pterional craniotomy, the incision is evident here. The initial part of the incision involves the frontal part of the opening. I use a wide spatula to undermine the scalp and separate the galea from the fascia of the temporalis muscle. The belly of the knife and not its tip is used for completion of incision. This maneuver efficiently prevents injuring the superficial temporal artery. The incision is about a centimeter anterior to the triggers to avoid injury to the superficial temporal artery. This artery can be palpated and the incision can be adjusted to avoid injury to the artery. Here's the dissection using the scissors to protect the superficial temporal artery, that is along the anterior aspect of the incision. Bovie electrocautery is used to cut the muscle as well as its superficial fascia. Next, the muscle's stripped away from the temporal bone. Some colleagues bluntly dissect the muscle from the bone in order to preserve the neurovascular structures, supplying the muscle, potentially decreasing the risk of delayed muscle atrophy and associated cosmetic deformity. So the Bovie electrocautery is minimized as much as possible around the underneath surface of the muscle to preserve the neurovascular structures there. Fish hooks are used to mobilize the scalp and the temporalis muscle and maximize the space exposed over the pterion. You can see now the frontal process of zygoma as it joins the frontal bone and the area of the keyhole. I prefer to place the initial bear hole just below the superior temporal line along the most posterior aspect of the bone that is exposed. I avoid placing the bare hole at the of the keyhole in order to avoid the bone loss that can also lead to further cosmetic deformity. Kerosene ron drawers are used to expand the bear hole, often there're epidural arteries at this area that have to be coagulated. You can see that the dissector will have a hard time in the area of the keyhole and has less flexibility in dissecting the dura away from the inner aspect of the calvarium. However, in this area, because the muscle is not present. I have much more flexibility in dissecting the dura from the inner table of the bone. By sweeping the dissector, I can go as far as the area of the pterion and thoroughly dissect the dura, minimizing the risk of dural tear, during completion of the bony cuts and with a footplate of the craniotal. The first cut is conducted over the temporal area. The foot plate may be gently rocked back and forth. So the foot plate can be used also as a dissector to strip the dura away from the inner surface of the calvarium. I go all the way to the area of the pterion, where further bra progress is not possible. And then turn the drill 180 degrees to create small amount of opening for the footplate to be removed. Next, a similar procedure is performed over the frontal area. You can see the gentle rocking motion of the drill in order to dissect the dura. I avoid sharp turns as it will lead to problems with further progress of the drill. This is a common mistake with the junior residents to try to make sharp turns with the drill. Now, the angle of the drill is turned slightly more forward. So that at all times the B one bit is perpendicular to the surface of the bone. Similarly, the drill bit is turned around itself and the bit is removed. A B one without a footplate drill bit is used to complete the osteotomy across the lateral aspect of the sphenoid wing and fender bone, as much as possible. Subsequently the bone flap is elevated. Sphenoid wing meningiomas can cause significant hyperostosis of the bone in this area and forceful manipulation of the bowl flap should be avoided as such manipulation can lead to a fracture, much more medially or the bone is not hyperaesthatic. This can potentially place the optic nerve and foramen at risk of a fracture. The latter aspect of the sphenoid wing is drilled away thoroughly. This portion of the bone is, again, hyperaesthetic because of the presence of the tumor. This is the superior orbital fissure that is being coagulated. The base of the tumor also can be coagulated and therefore the tumor can be partially de vascularized, a five millimeter lateral aspect of the, superior orbital fissure or the frontal temporal dural fold, or the menugal orbital band is cut to further allow exposure of the latter aspect of the clinoid process. The frontal edge of the craniotomy is thoroughly drilled flat with the roof of the orbit and all the gyrations, the bony gyrations over the orbital roof are also drilled, so that I can achieve a very flat trajectory toward the sub frontal area. This maneuver minimizes the need for frontal lobe attraction. As much as the orbiter roof is drilled away. Here's further bony removal along the latter aspect of the clinoid process. The bone is quite thick and hyperaesthetic. Bone wax may be used for hemostasis, for the bleeding from the bone. Minimal editing is done to provide the viewer with details of technique for execution of pterional craniotomy. The lesser sphenoid wing is further drilled away and the tumor is de vascularized extradurally. Here's the flat trajectory across the roof of the orbit. I did not expect the optic foramen to be affected by the tumor and therefore an exterior clinoiedectomy was not conducted in this patient. The dura is in size in a curvilinear fashion. The retention stitches are placed at the base of the dura. So maximal amount of dural mobilization can be performed to move the dura out of my working space. You can see the attachment of the tumor over the frontal dura. The tumor is aggressively de vascularized intaduraly. This is an important step, which will facilitate the later stages of the operation, including tumor decompression and dissection. The brain is protected using pieces of taffile or carotenoid patties. The heat from the intense light of the microscope can be quite problematic and causing cortical injury. Tumor devascularization is continued more medially. Next, the anterior limb of the Sylvian fissure is generously opened. So the borders of the tumor can be identified. The tumor capsule is generously coagulated. Bovie loops can be effective on very superficial meningiomas for efficient tumor removal. Obviously this device is not advised for skull based tumors where the ultrasonic aspirator is safer. Now I continue devascularization of the tumor all the way medially, while keeping in mind the location of the optic nerve. Aggressive tumor de bulking is undertaken. Now that tumor is mobilized away from the frontal lobe. Some invasion of the pier is encountered Carotenoid patties are used to wipe the brain away from the decompressed tumor. Here's further de bulking of the tumor to allow flexible mobilization of the capsule away from the medial neurovascular structures. This is a very important step to facilitate aggressive mobilization of the tumor away from the neurovascular structures rather than vice versa. The tumor is mobilized again, away from the frontal lobe. By measuring my distance along the lesser sphenoid wing, I can estimate the location of the optic nerve. Some of the tumor on the more lateral aspect of the sphenoid wing are further de vascularized and transected. The first important maneuver is now to find the approximate location of the nerve and carotid artery along the medial capsule of the tumor. And more anteriored and desired to be able to find the optic nerve. So I continue devascularizing the tumor more posterioly until the optic nerve entering its foramen is identified. I identify these important neurovascular structures as early as possible, along the anterior and medial aspect of the tumor capsule. There arachnoid bands are carefully protected. As expected, this tumor did not infiltrate the optic foramen. Now that I know where the important neurovascular structures are, I can be more aggressive in devascularizing, the more medial base of the tumor. Blind coagulation across the base is inefficient and places the important neurovascular structures that are located in medially at risk. Again, the arachnoid bands are respected as much as possible. The important principle remains, finding the neurovascular structures early on and keeping them out of harm's way. Next. I try to mobilize the tumor capsule from the poster funnel cortices and temporal cortices. It's best to decompress the tumor and mobilize it away from the brain rather than vice-versa. Falling further tumor de bulking, I was able to mobilize the superior pole of the tumor into the resection cavity. The MC branches were not significantly affected by the tumor capsule. This large piece of the tumor, was easily delivered and extracted. It's last attachments are coagulated and cut. Here's the resection cavity that will be in view momentarily. Additional tumor along the anterior aspect of the temporal dura is shredded away. And the part of the dura that cannot be resected is heavily coagulated to prevent the risk of future tumor recurrence. You can again appreciate the optic nerve. The carotid artery just slightly more posterior to it. The arachnoid membranes over them are left intact to protect them. This is a post operative MRI, which demonstrates complete resection of the tumor without any complicating features. Thank you.
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