Background and objectives Access through the foramen ovale (FO) is essential in performing trigeminal ganglion injection, glycerol rhizolysis, balloon compression, and radiofrequency thermocoagulation (RFT) to treat idiopathic trigeminal neuralgia (ITN). However, identification of the FO under fluoroscopy can be difficult and time-consuming, and thus exposes patients to increased radiation and procedure risks. Here we present the ‘H-figure’ as a novel fluoroscopic landmark to quickly visualize the FO.

Methods The H-figure landmark can be recognized as the medial border of the mandible and the lateral edge of the maxilla as the two vertical lines, and the superior line of petrous ridge of temporal bone (S-P-T line) as the horizontal line, and the FO fluoroscopic view is then optimized at the center of the H-figure immediately above the S-P-T line. We applied this landmark in a clinical cohort of 136 patients with ITN who underwent fluoroscopy-guided RFT of the trigeminal ganglion. We also compared the H-figure method with the traditional method. The primary outcome was the total number of fluoroscopic images required to visualize the FO (as a proxy of radiation exposure). Secondary measures included the procedure time required to finalize the FO view and the sensory testing voltage for paresthesia.

Results With the H-figure approach we were able to view the FO with an average of 4.2 fluoroscopic shots at an average time of 6.8 min. When compared with the non-H-figure traditional technique, the H-figure method required almost half the fluoroscopic shots in nearly half the procedure duration time, and paresthesia was evoked with half of the voltage.

Conclusion The H-figure is an easy fluoroscopic landmark that can help to view the FO with less radiation and procedure time, and the needles placed with this approach can be closer to the target for the RFT treatment of patients with ITN.