Clinical Scorecard: Enhancing frameless stereotactic guidance for accurate targeting of the foramen ovale during radio-frequency thermal ablation for trigeminal neuralgia in sedated patients utilizing triggered electromyography

At a Glance

Key Highlights

• RFTA is preferred for TN patients with prior microvascular decompression, multiple sclerosis, or trigeminal nerve damage.
• Traditional awake RFTA relies on patient feedback, which can be unreliable and uncomfortable; T-EMG allows guidance under general anesthesia.
• The novel technique achieved 96% success in FO cannulation with intact mastication post-procedure and 61.5% of patients reporting pain improvement.

Guideline-Based Recommendations

Diagnosis

• Classify TN according to International Classification of Headache Disorders (ICHD-3) into classic, secondary, idiopathic TN, or persistent idiopathic facial pain.

Management

• Consider RFTA for patients with TN, especially those with prior MVD, MS, or nerve damage.
• Utilize frameless stereotactic navigation combined with triggered EMG for accurate FO targeting during RFTA under general anesthesia.

Monitoring & Follow-up

• Intraoperative neurophysiological monitoring using T-EMG to detect compound muscle action potentials (CMAP) from the masseter muscle.
• Adjust stimulation intensity to submaximal activation to confirm FO cannulation and guide electrode trajectory.

Risks

• Potential intraoperative complications include damage to cranial nerves III, IV, VI, carotid artery injury, and mastication weakness.
• Anatomical variations and calcification of FO, especially in elderly patients, may complicate cannulation and increase risk of RFTA failure.

Patient & Prescribing Data

26 patients (17 females, 9 males) aged 24-79 years with various TN subtypes undergoing 27 RFTA procedures.

96% success in FO cannulation using T-EMG guidance; median stimulus intensity 4.5 mA; 61.5% experienced pain improvement; all patients retained mastication function post-procedure.

Clinical Best Practices

• Place needle electrodes in the masseter muscle prior to incision for T-EMG monitoring.
• Convert Tew trigeminal needle stylet into a monopolar stimulation probe using an alligator clip connected to a neuromonitoring system.
• Use stereotactic navigation and fluoroscopy to guide needle to FO border, confirming location by eliciting CMAP in masseter muscle at submaximal stimulation.
• Advance needle through FO toward Gasserian ganglion with continuous stimulation to differentiate nerve branches and target specific divisions (e.g., V2).
• Perform RFTA under general anesthesia with intraoperative neurophysiology to improve patient comfort and procedural accuracy.

References

• International Classification of Headache Disorders (ICHD-3)
• Cadwell Cascade Pro neuromonitoring system
• Boston Scientific Tew Trigeminal Needle Stylet