Novel fluoroscopic landmark to significantly facilitate the visualization of foramen ovale in treating idiopathic trigeminal neuralgia

Abstract

Background and objectivesAccess 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.MethodsThe 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.ResultsWith 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.ConclusionThe 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.

Identification of Foramen Ovale With H-Figure Fluoroscopic Landmark Improves Treatment Outcomes in Idiopathic Trigeminal Neuralgia

“…Because fluoroscopic visualization of FO with classic approach is difficult and time-consuming, which contributes to risk of mispunctures, 11,[13][14][15][16][17][18] we recently developed H-figure as easily recognizable fluoroscopic landmark to view FO in clinical practice. 7 In this 12-month follow-up retrospective cohort study, we showed that the H-figure approach was not only associated with substantially accelerated identification of FO with less fluoroscopic radiation, but also provided a better view of FO. More importantly, RFT performed utilizing the H-figure approach was associated with closer needle placement to the nerve targets as detected by lower paresthesia threshold voltages and was associated with better long-term pain alleviation across the entire 12-month follow-up period.…”

“…1,2,19 As the first element, the optimized FO view can be easily adjusted close to maximum width-to-length ratio using fluoroscopic H-figure landmark. 7 Many anatomical studies of human FO parameters suggested that the maximum width-to-length ratio of FO is around 2:3, [20][21][22] while other studies suggest that the width-to-length ratio of FO ranges from 1:3 to 2:3. [23][24][25] As it is impractical to measure the size of FO with fluoroscope, we relied on the width-to-length ratio of FO as a proxy for the quality final fluoroscopic view of FO.…”

“…On the other hand, if the FO was viewed as a narrow ovale or even a linear shape, then the fluoroscope was rotated in caudal or cephalad direction along the sagittal plane to acquire better visualization of the FO with greater width-to-length ratio. 7 Once the FO view was finalized, the grade scale of FO view was assessed by grades 1 to 3 (grade 1 = width-to-length ratio ≤1:3, Figure 3C; grade 2 = width-to-length ratio between 1:3 and 2:3; and grade 3 = width-to-length ratio ≥2:3, Figure 3D).…”

“…Compared with the classic approach group, the H-figure approach group was associated with better pain relief after the procedure (Table ), with significantly fewer patients H-figure approach group who had facial pain 3 months (6.6% vs 17.0%, P = .012) and 12 months (21.3% vs 38.0%, P = .005) after the procedure (Figure 5A). Among patients who had facial pain after the procedure, patients in the H-figure group had significantly less pain 6 months after the procedure (VAS median [IQR]: 3 [2][3][4][5][6] vs 6 [4][5][6][7], P < .001) (Figure 5B).…”

“…With H-figure fluoroscopic landmark, the FO fluoroscopic view can be easily optimized above the S-P-T line at the center of the H-figure when the medial end of the temporomandibular joint is located midpoint between the lateral and medial borders of mandible. 7 Compared to the classic approach, RFT needle inserted by the H-figure method required lower electrical stimulation to elicit paresthesia in affected area after FO puncture, 7 suggesting that the needle tip from the H-figure approach is closer to the target trigeminal ganglion branches. However, it remains unclear if RFT performed with H-figure has better clinical outcomes.…”