Percutaneous trigeminal radiofrequency rhizotomy technique

Adapted technique.

NB: needle insertion and/or lesioning may cause HTN, consider monitoring BP. Use either a straight electrode (bare 5 mm for 1 division, 7.5 mm for 2 divisions, or 10 mm for total lesions) or a curved electrode.

Electrode insertion

1. attach ground electrode to patient’s upper arm

2. prep the cheek on the involved side with Betadine

3. entry point: under short-acting anesthetic agent—e.g. propofol (Diprivan®) or methohexital (Brevitol®) — insert electrode-needle 2.5–3 cm lateral to the oral commissure

4. trajectory:

a) palpate the buccal mucosa with a gloved finger inside the mouth (lateral to the teeth)and with the other hand pass the electrode medial to the coronoid process of the mandible (keeping the needle deep to the oral mucosa, i.e., outside the oral cavity), initially aiming towards the plane intersecting a point 3 cm anterior to EAM and the medial aspect of the pupil when the eye is directed forward. Be careful not to contaminate the field with the hand that was in the patient’s mouth

b) as insertion progresses, use fluoroscopy to direct the tip towards the intersection of the top of the petrous bone with the clivus (5–10 mm below floor of sella along clivus)

c) upon entering foramen ovale the masseter often contracts, causing the jaw to briefly close. Remove the stylet, look for CSF to verify location (may not occur in re-do cases), and insert electrode through needle

In difficult cases, intraoperative fluoroscopy may assist in localizing the needle to Meckel’s cave and to R/O e.g. entry into superior orbital fissure (which can cause blindness after lesioning), or entry into foramen spinosum (middle meningeal artery). If necessary to visualize (e.g. when there is difficulty entering), the foramen ovale is optimally seen on a submental X-ray by hyperextending neck 20° and rotating head 15–20° away from the side of pain.

: from the tip of the electrode, when available, may help indicate the location of needle tip. Impedance: CSF (or any fluid) low (≈ 40–120 Ω); connective tissue, muscle, or nerve is usually 200–300 Ω (maybe up to 400 Ω); if > 400 Ω this likely indicates electrode is contacting periosteum or bone. After starting the lesion, impedance often goes down by 30 Ω transiently, and then as the lesioning continues it gradually returns to baseline or ≈ 20 Ω above it. If char develops on the electrode tip, the impedance will read higher than where it started.

Dharnipragada R, Mulford K, Woolums M, Nixdorf DR, Haines S, Grande A, Darrow D. Impact of Percutaneous Radiofrequency Rhizotomy Temperature on Trigeminal Neuralgia Relief. World Neurosurg. 2023 Mar 18:S1878-8750(23)00392-3. doi: 10.1016/j.wneu.2023.03.070. Epub ahead of print. PMID: 36940809.

Once the foramen ovale is entered, the needle is positioned with the following guidelines: for V3 division lesion the curved electrode should be just short of the clivus and pointing down, for V2 it is at the clivus and directed up, for V1 it is 5 mm beyond clivus and pointing up. ✖ At no time should the needle tip extend > 8 mm beyond clival line (to avoid Cr. N. III or VI complications). The patient is allowed to wake up and is stimulated through the electrode with the following set- tings: frequency = 50–75 Hz, 1 mS duration, start at 0.1 V amplitude and slowly increase (usually 0.2–0.5 V is adequate, higher voltages may indicate that the needle is not near the target and that stimulation is due to far-field currents; however, in previously lesioned patients up to 4 V may some- times be necessary). If stimulation does not reproduce pain in the distribution of the patient’s TGN, then the amplitude is returned to 0, the electrode is repositioned (straight electrode: advance nee- dle < 5 mm at a time, until the tip is in the vicinity of the clival line; curved tip electrode: advance and/or rotate); then slowly elevate the voltage again from 0 and repeat the repositioning-stimulating process until stimulation reproduces the distribution of tic pain. If previous lesions have produced analgesia and the patient cannot feel the stimulating current, one may stimulate at 2 Hz and watch for masseter twitch (requires preserved motor root).

When stimulation produces pain in the involved distribution of the TGN, perform the first lesion under short-acting anesthesia at 60–70 °C × 90 sec. A facial flush may be noted.139 After every lesion, perform a post-lesion assessment (see below). The goal is analgesia (but not anesthesia) in the areas of tic pain and hypalgesia in areas of trigger points. An average of three lesions are necessary at the first sitting, each ≈ 5 °C higher than the previous for 90 seconds. Anesthetic may not be needed after the first lesion if moderate analgesia has been produced by previous lesions.