Turning a pterional crani

- For aneurysms: Mannitol, decadron at beginning of case. Neuromonitoring with SSEP/EEG. For these cases, anesthesia is ok to paralyze. You should be in burst suppression by the time the dura is opened. When anesthesia hears your drill, they should start pushing the propofol.
- For tumors: variable. If operating near motor strip, we will often do MEP (if tumor is near corticospinal tract) and/or phase reversal (if you need to localize motor strip for cortisectomy planning or if tumor is near surface), no paralytics.
- If using stealth, cannot do any movement that break the bed after registration (i.e. cannot do head of bed up, can only do Tberg/reverse Tberg/airplane). When you raise or lower the head of the bed or the feet, it can make your stealth inaccurate by up to a cm. Doesn't make sense because the head is in pins locked into the mayfield, and the stealth arm is also locked into the mayfield, but this is the way it has been shown to be. (shrug).

- Supine, operative side facing out, ET tube on anesthesia side, tape eyes with tegederm (wait until after registration if using stealth - typically necessary for tumors and distal aneurysms) xeroform in ears.
- Pin with two ipsilateral, one contralateral -- something like picture below, but I typically like to pin a little closer to ear -- (see two blue dots) one superior and posterior to middle of pinna, one a few inches posterior and superior to that. Contralateral pin lateral above eye, close to hairline (green dot).

- Position head so malar eminence (pink dot) is highest. this will require rotation, extension, and significant translation of head superior relative to neck. 

- Incision from 1cm anterior to ear, straight up vertically until you are at superior temporal line, then slope over behind hairline to widow's peak. stay behind hairline. The sooner you slope over towards the face (i.e. if you were to go directly behind hairline) the more frontal lobe exposure you will get, the more you stay straight (or if you were to even swing back over the ear towards the back of head) the more temporal exposure you will get.

- Over non-temporalis: knife to bone.
- Over temporalis: knife through galea, bovie through temporalis to bone. Bovie temporalis below superior nuchal line so you leave a cuff of fascia on the bone flap.
- Position periosteal at root of zygoma, push up to get temporalis off in one flap. Advance flap until orbital rim.
burr holes, in order

Drilling
- The more burr holes, the easier it is to turn the crani. But the more (potential) cosmetic defect. In younger people with good dura, you can get away with fewer, but in old people with crappy dura that's all stuck to bone do at least 3 and do good dissection with woodson and penfield 3.
- You're not a badass if you can turn the crani through one burr hole if you're driving the strugglebus for 20 minutes with the footplate or if the dura looks like shit afterwards.
- 1. root of zygoma (blue dot)
- 2. modified keyhole (see photo) -- this is going to be slightly more superior than traditional keyhole. put drill on the spot I put my finger, and aim towards frontal lobe with perforator, you will end up on the red circle, directly on top of orbital rim. The goal is to make your crani with your footplate flush with the floor of the anterior fossa. That way you can get under the frontal lobe. If turn your crani too high on the forehead, you will have to rongeur down the frontal bone until you get the floor of the anterior fossa, and you will make an irreparable bony defect right on the patient's forehead, which will look bad, and they will be really pissed and think you are a shitty surgeon, which you are if you do this. To find the floor of the anterior fossa: feel the thickness of the orbital rim on patient, that distance represents the thickness of the rim all the way over the eye. Right above that will be the floor of anterior fossa.

3. Some spot inferior to superior nuchal line (so that it will be buried under temporalis) superior and posterior to burr hole #1.


Grey represents the rough locations of the frontal and temporal lobes -- the pterion is right on sylvian fissure. The more anterior you turn your crani, the more frontal lobe exposure you get, the more posterior and inferior you turn it, the more temporal lobe exposure you will get. Do you see how if you want more temporal lobe exposure, you angle your incision more posterior? So if you're doing a middle fossa crani your incision is posterior auricular, straight line up and down.

Sorry for my shitty handwriting

The top image is the order to drill - from superior temporal burr hole to keyhole (hypothetically less risk of getting into frontal sinus if you come from back to front), then inferior temporal burr hole to superior temporal burr hole. The further you curve this posterior, the more temporal lobe exposure you will get. Then come from the keyhole backwards towards your inferior temporal burr hole until you hit the sphenoid wing, then go the other way. you will likely need to curve superiorly as you drill near the sphenoid wing, thus getting a little heart shaped crani. You can crack the bone flap to get it off, but be careful - sphenoid wing connects to anterior clinoid, and you can propagate the fracture to the skull base, resulting in damage to optic nerve or carotid!

Then you need to drill off the remaining sphenoid wing until you hit the meningo-orbital band. Most people will retract the dura gently and/or put an instrument between drill and dura to protect it (i.e. penfield 1 or 3) however be careful, you can 100% cause contusions of the brain through the dura if you push on it too hard, and if you're on the left side this is prime real estate (brocas/inferior central sulcus/STG).

As an additional slick move, if you bevel the frontal/temporal bone (i.e. smooth out inner corner) you can get extra visualization/more retraction of dural flap.

Cut the dura in a c-shape with the flap/hinge at the sphenoid

Splitting the fissure
- knife through thickest arachnoid
- use fukushima suction to retract in your left hand
- use microtip bipolar in your right hand, insert tips closed, then open them to spread the arachnoid tissues

Anterior clinoidectomy

To access proximal ICA aneurysms (i.e. ophthalmic) you will typically need to drill off the anterior clinoid. Note: this is very high risk for injury to optic and ICA. The morbidity of these procedures is the reason why pipelines were invented.

1. Drill clinoid over the optic nerve until you unroof it. Use a diamond drill (cutting drills are too high risk of injuring surrounding structures) - your assistant must irrigate very aggressively, as the heat from the diamond is enough to cause thermal injury to nerve. This is very risky and requires very good drill control. 

2. Drill across top of clinoid from SOF (which is lateral; SOF is actually in the middle fossa). Previously, you should have dissected arachnoid/dural attachments off until you are able to reach the SOF.

3. The optic strut is a vertical piece of bone that lies between the optic canal and the SOF. If you drill straight down (where the circle'd X is) you will be drilling through the optic strut. you typically won't be able to drill all of it, and will have to crack it off. 

There is usually a loop of dura over the ophthalmic - this is the falciform ligament, and usually needs to be cut. Sometimes you have to cut the distal dural ring as well.