Setup

For Zenonos, you will need a Greenburg. 

For Gardner, you will need both a Greenburg and a Layla bar. 

Medications

Gardner: 10 dex, 0.5 g/kg mannitol, Ancef, no Keppra

Monitoring

This is likely variable and dependent on attending and pathology. Brain stem auditory evoked potentials are always used. Often, monitoring will include the ipsilateral CN 4, 5, 6, 7, 9, 11, and 12. 

Pinning

The head is always pinned. Have an assistant hold the head, elevate, and rotate towards the contralateral side. 

Zenonos

Double pins are occipital, in the sagittal plane, biased slightly off midline away from the side of the tumor. The single pin is in the forehead, at about the contralateral mid-pupillary line. 

Gardner

Double pins are contralateral to the pathology, one on the mastoid and one on the superior temporal line. Single pin is anterior, just behind the hairline and at the superior temporal line. 

Positioning

Gardner and Zenonos

First, turn the bed such that the side of the pathology is facing away from anesthesia. The bed should be parallel to anesthesia. Push the bed down until the feet touch the booms at the base of the bed. 

An assistant should hold the head and endotracheal tube while the patient is positioned. Turn the patient lateral. Move the patient away from anesthesia until the back is flush with the edge of the bed. Next, move the patient north until the dependent arm is on the head of the bed, ready to drop down into a sling when the head of bed is removed. Place an axillary roll in such a way that it will stay under the patient when the head of bed is removed. 

Pad the legs with purple foam under the dependent knee and a pillow between the knees and ankles. 

Make sure the belly fat graft site is undraped. The site is a few inches lateral to the belly button. 

Wrap the upper arm in a large purple foam and loosely secure to the patients side by going around the bed with 3-inch tape. Above and below the elbow. 

Have someone hold the dependent arm before removing the head of the bed. The dependent arm will drop once the head is removed. Remove the head of the bed and attach the 360-degree Mayfield. Hold the head in its final position. Place your hand under the patient's neck and tilt the head towards the floor. Flex the neck slightly. Secure the Mayfield to the inside attachment of the head clamp. 

Wrap the dependent arm in purple foam and allow it to settle against the arm of the Mayfield. Fold a pillow in half width-wise and stuff into the remaining space between the dependent arm and the Mayfield. 

Pull the upper arm down towards the head of the bed with 3-inch tape. Tape goes on top of the shoulder and is pulled down to the foot of the bed nearer anesthesia. 

Image guidance attaches the guidance arm on the outside attachment of the Mayfield and positions it such that the tracker is on the same side as the patient's face.

Marking

Zenonos

Cranial incision

Use image guidance to mark out the transverse and sigmoid sinuses and the transverse-sigmoid junction. Mark the inferior edge of the transverse and medial (posterior) edge of the sigmoid. 

Mark the approximate location of the craniotomy itself. 

The skin incision is a large U-shape with the ear at the base of the pedicle. It should extend far enough posteriorly to allow about 2 cm of clearance from the edge of the marked craniotomy. 

Fat graft incision

About 4 cm long, several cm lateral to the belly button, oriented in the axial plane. 

Prep

Chloraprep both the cranial and fat graft sites. Zenonos preps once then uses gives local lidocaine with epi to the cranial incision. 

Gardner

Cranial incision

There are 3 ways Gardner uses to approximate the level of the transverse sinus: 

1. Along a line drawn from the root of the zygoma to the inion
2. Along a line in the axial plane at about 2/3 of the way up the pinna (see mark on the pinna in image below)
3. At the superior nuchal line

There are two ways to approximate the level of the sigmoid sinus: 

1. Feel for the digastric groove of the mastoid process, carry this line upward towards the transverse sinus, biased medially (e.g. towards the back of the head). 
2. Feel for a "flat spot" at the base of the mastoid that approximates the level of the asterion. 

The skin incision is an upside-down L-shape. After marking, scratch the incision with a safety pin then dye with methylene blue. 

Draping

Zenonos

For the cranial incision, three blue towels are used. One across the base of the skin incision pedicle, covering the ear. One along each arm of the U-shaped incision. Collectively, the towels describe an equilateral triangle. 

For the belly incision, just four towels in a square. 

Place a down sheet. 

Drape the fat graft site first using a thyroid drape. Pull this down to the feet and up to the shoulder, but not past. Then, use a crani drape for the cranial incision. 

Place a Greenberg retractor system such that one arm is in front of the head, parallel with the face, and the other arm is parallel with the occiput. Both arms should be low in the field, but not so low that the fish-hooks put pressure on the ear and face. 

Gardner

Four towels for the cranial incision in a square. Four towels for the belly fat graft in a square. 

Thyroid drape for belly, crani drape for head. 

Gardner does not use a Greenberg retractor. He uses a Layla bar. 

Approach

Zenonos

Zenonos uses a differential musculocutaneous flap.

Skin

Incise the skin to the subdermal fat, stopping at the fascia/galea. Dissect within the plane between fascia/galea and subcutaneous fat and carry the dissection towards the ear until the whole flap is free. As you approach the ear, the skin becomes very thin and special care should be taken not to poke through the skin. 

Muscle

Use a Bovie to cut through the fascia and muscle to the bone. The muscle incision starts at the apex of the U-shaped skin incision and is carried anteriorly, along the superior border of the skin incision, to the anterior limit of the exposure. Here, it curves down towards the mastoid and is carried to the mastoid tip. You should see the digastric groove at the far inferior limit of the muscle incision. Use a curved Adson periosteal to elevate the muscle flap. Use a Penfield 1 to dissect the muscle from the bone overlying the transverse and sigmoid sinuses. Use fishhooks to retract the muscle flap posteriorly and the muscle cuff anteriorly. 

Cut a large piece of Bicol collagen sponge, place over the muscle flap, and wet it. This keeps the muscle from drying out and shrinking under the heat of the microscope. 

Bone

The borders of the craniotomy are the inferior edge of the transverse sinus, the posterior edge of the sigmoid sinus, the tip of the mastoid inferiorly, and a few mm anterior to the muscle flap posteriorly.

Use an M8 drill bit. Start at the bottom, where the bone is thinnest, define your depth, then work around. Gently remove the bone flap. 

Thin the bone covering the transverse and sigmoid sinuses and carefully remove. Expose the bottom 1/3 of the transverse sinus and posterior 1/3 of the sigmoid. The degree of exposure of the sinus depends on the patient's anatomy and should be dictated by the attending. 

Dura

Incise the dura in a U-shape with the opposite orientation to the skin incision. Leave a small cuff of dura adjacent to the sinuses. One leg of the incision parallels the transverse sinus. The next parallels the sigmoid. The final leg parallels the transverse sinus incision. 

Cover the dural sinuses with Bicol to keep them wet. 

Retract the edge of the dura proximal to the sigmoid sinus with 4-0 Neurolon sutures.Two bites are passed through the dura - the first from inside out then from outside in. Both ends of the suture exit on the inner side of the dura. This everts the dural edge. Pass the suture through the plastic part of the fishhooks and tie tightly. 

Gardner

Gardner uses a differential flap when the lesion extends medially. When the lesion is small and there is no need for medial exposure, he raises the entire flap as a single myocutaneous flap. 

Skin and Muscle

Myocutaneous flap: 

For the musculocutaneous flap, use the Bovie to go straight down to bone deep to the skin incision and open the whole L-shape. 

Use fishhooks to retract the musculocutaneous flap to the Layla bar. 

Differential flap: 

When Gardner does a differential flap he uses a C-shape skin incision, like Zenonos does. Make skin incision with a #10 blade just through the dermis. Then, use a Bovie with a Colorado tip set to 20 to develop the plan between galea and the fascia of the muscle. 

For the muscle, start on the tip of the mastoid with the Bovie and go straight down to bone. Then, draw the Bovie superiorly towards the transverse sinus and turn 90 degrees towards the occiput once you've passed the transverse. Go medially (towards the occiput) until the edge of the skin incision before turning inferiorly. Elevate the muscle with a Bovie while your assistant applies gentle traction on the muscle flap with a curved Adson periosteal. 

Bone

Cross the transverse sinus superiorly. Stop the initial craniotomy just medial to the medial border of the sigmoid sinus. 

Use an M8 drill bit. Start at the bottom, where the bone is thinnest, define your depth, then work around. Gently remove the bone flap. 

Thin the bone covering the sigmoid sinus and carefully remove. Be sure to skeletonize the emissary vein and coagulate with the bipolar. 

Dura

The dura is pedicled against the sigmoid sinus. Incise in a U-shape with the opening of the U against the sigmoid. Leave a small cuff of dura against the transverse. 

Open the inferior-most limb of the dural incision first and watch for herniation of the cerebellum through the dural defect. If there is excessive herniation, don't open the rest of the dural incision. Instead, open the cerebellomedullary cistern and let off CSF. Once the cerebellum is sufficiently relaxed open the rest of the dura. 

Cover the dural sinuses with Bicol to keep them wet. 

Tack up the dural flap with 4-0 Neurolon to the muscle. 

Retract the edge of the dura proximal to the sigmoid sinus with 4-0 Neurolon sutures in standard fashion (not the way Zenonos does it to evert the edge as above). 

Snake Retractor

Before putting the retractor on the Greenburg, loosen all the joints, hold it upside down, and allow it to dangle. Tighten the joints when it is in a straight configuration. 

 Attach the blade to the snake retractor as demonstrated in the image. The dial should be oriented away from the patient and the blade should be parallel with the snake. 

 Attach the C clamp to the Mayfield followed by a single angled attachment. Angle the attachment as far down, towards the floor, as you reasonably can. 

Attach the snake arm to the Greenburg with the dials pointed towards you. To get the retractor at the level of the incision, allow the snake arm to bow outwards, toward the operator, until the length is appropriate. 

Place a rubber half-by-three rubber dam on the cerebellum then cover it with a half-by-three regular patty. This is the landing strip for the brain ribbon. Place the brain ribbon on the patty and do not apply any significant traction to the cerebellum. It is just a resting point for the otologist's hands and drill. 

Closure

Close the dura in a watertight fashion. Gardner is more likely to use a pericardial graft. 

When closing the dura, follow these principles: 

1. Always sew from flap to dura (island to land)
2. Start at the inferior edge, then the posterior edge, and end with the superior edge. This makes it so you can fill the cavity with saline from the top just before you finish closing. 
3. Make sure the pericardial graft is appropriately sized and don't leave dog-ears. 

Plate the bone. Use the long dog bones that have two holes on each side (for a total of four holes in each dog bone). The dog bones are placed at a 90-degree angle to one another. One at the posterior edge and the other at the superior edge. The arrow marks the lateral border of the flap, toward the sigmoid sinus. 

Use bone cement to fill the gaps in the bone. 

Zenonos

Close the muscle and fascia with 3-0 polys. Close the deep dermal layer with 3-0 polys. Run a 4-0 Biosyn over the skin, baseball stitch. Put skin glue on top of the baseball stitch. 

Gardner

Close the muscle and fascia with 2-0 polys. Close the deep dermal layer with 3-0 polys. Run a 3-0 Nylon over the skin, baseball stitch. Cover with Bacitracin and a Telfa stapled in place.