Monitoring

Depends on pathology, usually SSEPs, EEG, transcranial MEPs, and possibly cranial nerve EMG depending on which cranial nerves are at risk. 

Equipment

Layla bar - set up on the side contralateral to the pathology as high up on the bed as it will go. 

Setup

Turn the bed 180 degrees.

Lang uses the bean bag,

Pinning

Remove the head of the bed before pinning.

Always use the radiolucent Mayfield for vascular cases.

Single pin on the ipsilateral forehead. Double pin in the axial plane along the dependent part of the occipital bone. 

Head Position

1. Flex the neck
2. Turn the head towards the floor (i.e. the patient's line of sight is towards the floor)
3. Laterally flex the head towards the floor, drop the apex

Turning the head towards the floor is in contrast to how Gardner and Zenonos position the head for a far lateral.

Positioning

Lateral position with the dependent arm wrapped in purple foam and allowed to rest in the angle of the Mayfield. 

Sandwich the upper arm between two pieces of large purple foam, then place a Tegaderm on the shoulder. Tape on top of the Tegaderm and secure the shoulder back to the edge of the bed before wrapping that arm in purple foam and wrapping around the bed a couple times. 

Flex the neck slightly then rotate so that the patient's gaze is towards the floor. 

Layla Bar

Position the bar such that it is parallel with the horizontal limb of the skin incision, at approximately the level of the shoulder. 

Marking

Start at the mastoid tip and draw a line along the expected location of the sigmoid sinus. Begin curving medially (i.e. towards the occiput) above the level of the transverse sinus. Take this line medially until you reach the external occipital protuberance, then curve down in a straight line along the spinous processes to the spinous process of C2. 

Approach

Begin skin incision with a #10 scalpel blade on the topmost horizontal part of the incision. Incise through the dermis to the subcutaneous fat. Your assistant develops the subgaleal plane with Metzenbaum scissors, then you will Bovie on top the scissors. You will encounter the occipital artery at the midpoint of the horizontal incision. 

Use fishhooks to retract the skin and subcutaneous fat towards the feet, where the Layla bar is positioned. This puts the incision under tension and facilitates the next step - dissecting towards the feet in the plane between the galea and the fascia of the muscle. Develop this plane for about an inch or so. The inferior limit of this dissection plane is when you feel that you are past the nuchal line. When you are past the nuchal line, make a horizontal cut with the Bovie through the fascia and muscle straight down to the bone. The fascia/muscle Bovie incision parallels the horizontal skin incision about an inch below it (i.e. towards the feet). This leaves a ~1 inch cuff of muscle to sew to on closure.

Now, turn your attention to the part of the incision behind the ear. Go through the skin with the #10 scalpel blade then take the Bovie straight down to the bone. 

Finally, turn your attention to the midline suboccipital incision, which you should develop in the same way as you would for a Chiari or posterior cervical spine case. Expose in the midline avascular plane to the spinous process of C2. Lang exposes the C1 posterior arch and the ipsilateral C2 lamina. 

Under retraction from the fishhooks, use the Bovie to dissect the suboccipital musculature from the occipital bone. Expose the mastoid, the digastric groove, and the occipital groove (where the occipital artery passes). Now, with the Penfield 1, carry dissection caudally along the mastoid through the digastric groove towards the skull base. Here, you will see the flat, shiny surface of the inner articulating surface of the occipital condyle. 

Expose, with the Bovie, the posterior arch of C1 to a point about 1.5 cm from midline. Then, use a Penfield 1 dissector to dissect in the subperiosteal plane circumferentially around the C1 posterior arch. Extend the subperiosteal dissection laterally along the C1 arch. Expose the sulcus arteriosus but take care not to violate the periosteum or you will encounter bleeding from the venous plexus surrounding the vertebral artery. 

At this point, the muscle and soft tissue will be tethered to the occipital bone only at the point overlying the vertebral artery. Imagine a line connecting the occipital condyle with the posterior arch of C1. The vertebral artery lies along this line. To further release the suboccipital musculature, reposition the fishhooks such that the tethering tissue is under tension, then use the bipolar "cutting technique" to release the tissue. Depending on the treated pathology, you may choose to expose all, part, or none of the vertebral artery. 

Craniotomy

Begin by making a burr hole with the perforator at the transverse-sigmoid junction. Follow by making a burr hole at the midline superior occipital bone. Connect the two burr holes with a horizontal bone cut. Follow with a vertical midline bone cut to the foramen magnum. Finish with a vertical lateral bone cut from the transverse-sigmoid junction to the foramen magnum. This final bone cut necessarily curves medially to make it to the foramen magnum. Elevate and preserve the bone flap. 

With a 5-mm cutting burr, expose the transverse and sigmoid sinuses. Lang will dissect with the Penfield 1 between the bone and both the transverse and sigmoid sinuses. Once the bone has been sufficiently thinned by the cutting burr, he will bite it with a Kerrison. 

Continue exposing the sigmoid sinus caudally and follow as it curves anteriorly into the jugular bulb. At this point, you will have a triangular-shaped piece of bone left that constitutes the occipital condyle and, more rostrally, the jugular tubercle. The condylar emissary vein travels outside the occiput (along the dura of the craniocervical junction) before diving into the occipital condyle on its way to the jugular bulb. This should be skeletonized and bipolared or it will cause significant blood loss. 

The final step is drilling the occipital condyle using the 2mm diamond burr. The deep limit of this drilling is the cortical bone of the hypoglossal canal. Leave alone the part of the condyle adjacent to the atlanto-occipital joint, just drill the part of the condyle adjacent to the cerebellum. 

Dura

Use a #15 scalpel blade to open the dura in an upside-down hockey stick shaped incision. The first limb starts at the transverse-sigmoid junction, parallels the transverse sinus, and proceeds medially to the midline. Then, it curves down towards C1 in the midline and stops just shy of C1 itself. Lang will curve both ends of the dural incision inwards to facilitate a small amount of additional retraction. 

Closure

4-0 Nurolon for watertight dural closure followed by DuraSeal. 

Bone wax the any exposed mastoid air cells. Cover the dura with Nu-Knit. 

Use a small mesh to extend the bone flap to the drilled-away bone covering the sigmoid sinus. 

2-0 Polysorb to close the fascia and muscle. 2-0 Polysorb for the deep dermal layer. 3-0 nylon running baseball on the skin.