Rinoo Vasant Shah
Patient Position: Supine.
Indications: Trigeminal neuralgia (“tic douloureux”), cluster headache, ocular pain, cancer pain, surgical anesthesia, differential neural blockade, prognostic block for neurolytic procedures.
Needle Size: 16-gauge, 32-mm angiocatheter (introducer), 20-gauge curved, blunt Racz-Finch Kit (RFK needle; Radionics, Burlington, MA) is preferred or 22-gauge b-beveled needle, 3-mL syringe, T-connector tubing.
Medications: 0.2% ropivacaine and 2% lidocaine in a 1:1 mixture for block (0.25% bupivacaine or 0.25% levobupivacaine may be substituted for ropivacaine). Total volume of 1 to 2 mL with or without 40 mg methylprednisolone, 4 mg dexamethasone, or 40 mg triamcinolone acetate, plus Omnipaque (Amersham Health, Buckinghamshire, England) (iohexol) water-soluble contrast 240 mg/mL (0.5 mL).
Anatomic Landmarks: The trigeminal ganglion lies in the Meckel cave at the apex of the petrous part of the temporal bone. The mandibular branch exits the foramen ovale and is partly enclosed by a dural cuff (see Fig. 23-3).
1. Ipsilateral corner of lip: start 2 to 3 cm lateral.
2. Ipsilateral pupil: aim midline.
3. Ipsilateral auditory meatus: aim along line connecting entry and aim to a point 3 cm anterior to meatus, at proximal zygoma.
1. Submental view
Other relevant anatomy:
d. Petrous pyramid
2. Lateral view
Other relevant anatomy:
a. Petrous bone
c. Pituitary fossa
Fluoroscopically Guided Technique
After sterile preparation of the region, a submental or subzygomatic view is obtained. The anteroposterior view shows the petrous ridge through the orbits; 1 cm medially, it also shows a dip in the petrous ridge. The C-arm is then angled cephalocaudad and obliquely to visualize the foramen ovale just medial to the mandible and at the top of the petrous “pyramid.” A forceps is used to mark the surface entry point directly over the foramen oval. The site of introduction of the needle is about 2 cm lateral and 0.5 cm inferior to the labial commissure. A 16-gauge, 1¼-inch angiocatheter is introduced in gun-barrel fashion (i.e., through the “eye” of the needle). Then, a 20-gauge blunt, curved RFK needle is inserted through the angiocatheter in similar gun-barrel fashion toward the medial aspect of the foramen ovale. Surface anatomic landmarks may help but are usually unnecessary with fluoroscopy. Once the needle is at the level of at the foramen ovale, a lateral view is obtained. The needle tip should aim for the junction of the clivus and petroclinoid ligament. V1 is at this junction. V2 is 50% of the distance between the petrous pyramid and the junction between the clivus and petroclinoid ligament. V3 is at the junction of the clivus and petrous pyramid. The ideal location of the needle is approximately 1 mm beyond the clivus but never beyond 2 to 3 mm. Aspirate for blood and cerebrospinal fluid (CSF) (commonly occurs with sharp but not blunt curved needles) until negative, then instill the contrast. The trigeminal cistern should opacify. Initiate sensory stimulation at 50 Hz on a 0- to 2-V scale. Paresthesias are felt at 0.5 to 0.7 V, while around 2 V a contraction of the masseter muscle is elicited confirming the right positioning of the needle. Slowly instill 2 to 3 mL of the local anesthetic and steroid mixture. This is usually followed by the generation of a pulsed electromagnetic field radiofrequency at 42°C for a 120-second cycle times two to three cycles. Standard radiofrequency neurolysis can also be performed at 67°C for 90 seconds. This latter technique, however, is associated with a risk of sensory loss in the trigeminal nerve distribution. After the needle is removed, an ice pack is placed on the patient, and standard monitoring is maintained.
Complications: Masticator muscle weakness, corneal analgesia, seizure, coma, paralysis, total spinal anesthesia, keratitis, bacterial meningitis, carotid fistula, intracranial hemorrhage, diplopia, death, and facial or subscleral hematoma.
1. Initially, the needle is directed downward and laterally. Then, the needle is aimed medially for the foramen ovale to avoid mouth entry.
2. One finger should be placed in the mouth to prevent intraoral entry of the needle.
3. Prophylactic antibiotics and sedation with midazolam and fentanyl are advised.
4. If bone is contacted, the needle is “walked” posteriorly along the skull into the foramen ovale.
5. A 3-mL or smaller syringe should be used.
6. Free flow of CSF is not usually seen with a blunt, curved needle. The free flow of CSF simply implies that the needle is too anterior (i.e., Meckel cave, rather than in the trigeminal cistern).
7. If a sharp needle is used, the needle should be withdrawn until no CSF leaks back; otherwise there is a risk of total spinal anesthesia.
8. Small amounts of local anesthetic should be slowly injected to avoid the disastrous complication of total spinal anesthesia.
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Raj PP. Trigeminal block and neurolysis. MD Consult Pain Medicine, www.mdconsult.com. January 7, 2002.
Tew JM, Taha JM. Treatment of trigeminal and other facial neuralgias by percutaneous techniques. In: Youmans J, ed. Neurological surgery, 4th ed. Philadelphia: WB Saunders, 1996:3386–3403.
Waldman SD. Blockade of the gasserian ganglion. In: Waldman SD, ed. Interventional pain management, 2nd ed. Philadelphia: WB Saunders, 2001:316–320.