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Pterional Craniotomy: How Do I Do it?

April 27, 2016

Transcript

Pterional craniotomy is a work horse approach among cranial approaches. This video reviews the extended pterional craniotomy with some modifications to expand its operative reach through the sub frontal corridor. The patient is obviously placed in a supine position. I prefer to place the single-pin behind the ear, just above the mastoid groove with two pins along the superior temporal line contralaterally. This position of the skull clamp provides ample amount of space along the incision without necessarily any of the pins interfering with my working space. The malar eminence, is the highest point on the operative field. The turn of the head depends on the location of the pathology and its distance from the midline. The incision starts just above the zygomatic arch, continues perpendicular to the superior temporal line and then after that essentially stays just behind hairline. Really expansion of the incision to be more posterior and expose the frontal lobe is unnecessary for procedures that require a subfrontal approach toward the parasellar area. I connect the inferior edge of the incision to its superior one, that line should stay within a centimeter of the key hole. This configuration allows me and assures me reaching the key hole effectively during refreshing of the temporalis muscle, without any struggle. Now that we have reviewed the relative patient positioning details, let's go ahead and start the skin incision. Here is the skin incision with the use of the Raney clips. The belly of the 10 blade scalpel is used to reflect the galea. We have to make an incision to proceed with the subfascial versus interfacial technique. However, in this configuration, which is the most commonly used approach for typical pterional craniotomy without necessarily the use of orbital zygomatic osteotomy. There the temporalis muscle is mobilized in one layer as a myocutaneous flap with the scalp. The keyhole is exposed. The anterior reflection of the temporalis muscle as anteriorly as possible using the fishhooks is important to expose the lateral aspect of the sphenoid wing and the pterion, without interference of the muscle. I like the first burr hole to be placed just below the superior temporal line, along the most posterior aspect of the bony exposure. This single burr hole is quite adequate to dissect the dura away from the inner aspect of the skull bone. Many colleagues prefer a burr hole in this region, however, the bone loss in this area can be cosmetically noticeable. Secondarily, placing the burr hole has another advantage that the number three Penfield can be used to sweep the dura away from the inner scalp bone without the interference of the muscle with a number three dissector. If the dura is adherent, additional burr holes may be placed around the keyhole and just above this zygomatic route to ensure that it dura dissected away without any tear. Often, there is a branch of middle meningeal artery apparent here that can be coagulated. Carotid roungers are used to expand the burr hole. Here, you can see the sweeping action of the number three Penfield, that is not as available as you can see here because of the presence of the temporalis muscle. You can sweep all the way to the pterion and the sphenoid wing, if the burr hole is placed away from the temporalis muscle. Obviously the extent of bone removal depends on the location of the lesion, however, for a standard subfrontal approach, you can see that I stay just above the superior temporal line. Footplate is turned smoothly, the drill cannot make sharp turns. That often creates much resistance to the drill. The drill is turned 180 degrees and the heel is removed. The second osteotomy is performed more inferiorally. This is the thinner part of the temporal bone, the squamous part, and the drill can advance relatively quickly. You can see that the foot plate cannot advance further beyond the sphenoid wing, if the muscle has been advanced adequately anteriorly. The attachment of the bone flap to the pterion is drilled away using a B1 foot plate. You can see the voracious bleeding from the epidural space, in this patient that was suffering from a lateral sphenoid wing meningioma. Obviously this hypertrophied epidural vein is feeding the tumor and more developed. Now we'll go ahead and expand our subtemporal craniectomy, especially for this tumor that expands and fills the anterior temporal lobe. The lateral aspect of the sphenoid wing is aggressively drilled. We'll go ahead and place a couple of protective sutures, one in the temporal side of the bony exposure and one on the frontal side. you can see one here is already placed. We'll go ahead and place one on the temporal side. The sphenoid wing is aggressively removed. Axillar roungers. And then the drill may be used to further remove additional bone. Importantly, the hemostasis on the epidural space is crucial to provide efficient movements within the intradural space for completion of section, without unnecessary halting dissection periodically to achieve hemostasis. The critical part for an extended pterional approach is aggressive drilling along the roof of the orbit and the lateral aspect of sphenoid wing. Here, you can see that a retractor holds the dura while the lateral sphenoid wing is being aggressively drilled away, all the way to the superior orbital fissure. As we get closer to the mid portion of this sphenoidal wing the B1 bit without a footplate is used until the superior orbital fissure is exposed. You can see that the cortical bone over the subfrontal area just lateral to the roof of the orbit is drilled flush. Roof of the orbit. The gyrations on the roof of the orbit are also drilled away to provide as flat of a trajectory as possible. Please note how I am holding the drill to make sure there is no inadvertent slippage of the drill bit or the entire drill over the edges of the bone. Removal of these gyrations, aggressive bleeding of the orbital roof, provides some of the advantage of orbiter zygomatic craniotomy, without necessarily the risk of cosmetic deformity in this area. This element with aggressive resection of the lateral sphenoidal wing, define the extended pterional craniotomy. Now the dura is being opened. Not all the dura is necessarily excised, part of the dura can be left over the frontal lobe to protect the brain from the intense light on the microscope. The dural stitches are placed at the root of the dura and not at the edges to provide further mobilization of the dura and the temporalis muscle. A piece of Telfa is used to protect the surface of the brain during dissection. You can see the tumor that has extruded through the anterior part of the temporal lobe here. The frontal lobe is gently elevated and the optical carotid cisterns are opened to achieve brain relaxation. The contour of the sphenoid wing is followed until the optic nerve is apparent. Here, you can see, contour of the optic nerve just through the arachnoid bands. Here is the available arachnoid for opening and release of CSF for brain decompression. As you can see, retractors are now used. A bayoneted scissor is most likely more appropriate, however, in this situation under the magnified scope, CSF can be released, optic nerve protected. A piece of cotton ball may be placed, so this opening is maintained for additional CSF removal, during the rest of the case. Here is the carotid artery, just at the tip of my dissector.

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