Positioning

Supine on a regular OR table. Intubated with the tube secured to the side of the face opposite the patient's facial pain. Move the patient up in the bed until the tops of the shoulders are well clear of the break between head and main part of bed. Wrap the arms in big purple foams and burrito the patient with a few wraps of 3-inch tape. 

Remove the head of the bed and place the Mayfield arm. Attach the special head holder to the Mayfield arm. Position the patient's head such that the head holder is resting on the inferior-most part of the occiput. 

Attach the foot support to the edge of the bed.

Equipment

Always wear lead for this case. There is no need for a headlight or loupes.

Start with double gloves, you will remove the outer pair after putting your finger in the mouth. 

Imaging

Always use C arm. The detector side (wide side) of the fluoroscope should be on the opposite side of the patient's facial pain.

Marking

No need to clip hair.

Mark a dot 2 to 2.5 cm lateral to the most lateral edge of the corner of the lips.

For Dr. Zenonos, draw two lines: 

1. From the entry point to the medial border of the pupil
2. From the entry point to a point 2.5 cm anterior to the ipsilateral tragus

Prep

Prep the side of the face on which you will be operating with chlorhexidine wipes and then chlorhexidine.

Draping

Four blue towels in a square. Keep the eye and nose in the field. 

Lay blue towels at the inferior edge of the face and lateral edge of the face. Do not staple the towels. Use a down sheet as the main drape.

Procedure

First, make sure the C arm shot is a good lateral. Dr. Zenonos makes the external auditory canals line up on the lateral. 

Do not bend the needle. Sekula used to do this but Dr. Zenonos does not. Use a straight spinal needle.

Locally anesthetize the entry point and tract to the skull base with lidocaine without epi. 

Point the bevel of the needle medially and insert the needle at the entry point. 

Use a more lateral trajectory for the initial approach, until you reach the skull base. The dotted red line is the line marked at the start of the procedure. The black line is the initial trajectory, which is more laterally oriented to avoid going into the mouth. 

Insert your left finger into the mouth just once to ensure that you haven't perforated into the oral cavity. Remove your outer pair of gloves.

Once the needle is past the oral cavity re-orient the trajectory such that it is in line with the marked line (dashed red line in the image above). 

The cranial-caudal trajectory is determined by aiming for the location of foramen ovale on the lateral x-ray (red dotted trajectory).

Feel with the tip of the needle against the skull base until you feel the "give" of the needle passing through foramen ovale. Trial multiple trajectories along the medial-lateral line until you feel the needle go through. Be sure to back the needle part-way out before re-orienting to a new trajectory to be sure that it isn't falling down the same path as before. 

Once the needle is in place, remove the stylet and watch for egress of CSF. Once CSF is observed, inject 0.1 cc of contrast under continuous fluoroscopy. Watch for filling of Meckel's cave and movement of the contrast to the posterior fossa. The entry of the trigeminal nerve into Meckel's cave occurs beneath the tentorium. So, if the needle is in the correct space, contrast should go to the posterior fossa alone. 

In the image below, the needle is represented in red, the flow of contrast in yellow, and the tentorium in green. 

If contrast layers on top of the tentorium or is seen filling the sulci of the temporal lobe, the needle is incorrectly placed with a trajectory that is too lateral. 

How can your needle pass through foramen ovale, be intracranial, and end up in the temporal lobe? And why does this mean you're too lateral and not too deep? 

This is because Meckel's cave slants from inferolateral to superomedial on the coronal view. A trajectory that is too lateral will go through ovale, miss the arachnoid cistern of the Gasserian ganglion, and pass into the middle cranial fossa.  

In the radiograph below, the dotted red represents foramen ovale and the solid blue line represents the dura of the middle cranial fossa. 

To correct this, re-orient the needle trajectory to aim more medially. If this still doesn't work, you may need to change the entry point to be more lateral to help you get a more lateral-to-medial trajectory. 

Once the needle is in the correct position, move the OR table so that the patient is in a seated position with the back of the bed up. Also move the Mayfield arm to push the patient's head up. 

Inject 0.3 cc of glycerol. Do not push too hard on the syringe or you will detach the syringe and spill all of the glycerol.

Occasionally, you will use Depo-Medrol + bupivicaine instead of glycerol. This is indicated when the patient has a neuropathic component to their pain. Use of glycerol, an ablative agent, in this setting may worsen neuropathic pain. Depo-Medrol + bupivicaine will anesthetize the nerve and reduce inflammation and is a valuable alternative. 

Closure

Remove the needle. Dr. Zenonos does not use a Band-Aid. 

Keep the patient in the seated position and transfer the patient to the stretcher. The patient is subsequently extubated while sitting up. Keep the patient sitting up for 2 hours.

If you encounter significant venous bleeding, go to PACU and grab a bag full of ice. Hold ice to the patient's face during recovery in the OR, extubation, and on transport to the PACU. This will significantly reduce facial swelling.

The patient is to remain upright in PACU.

Follow up

Two weeks with Dr. Zenonos, no imaging, no antibiotics on discharge. 

Ask what he wants to do with the pre-op medications to treat trigeminal neuralgia. Sometimes he wants them stopped, other times continued.