Objective: Historically, in the use of radiofrequency lesioning (RFL) for trigeminal neuralgia, lateral fluoroscopy has been used for operative guidance. However, as with many other neurosurgical procedures, there is a growing body evidence to support the clinical utility associated with use of neuronavigation-assistance for RFL. There is a paucity of data in the literature investigating morphometric parameters associated with success of access to foramen ovale (FO) and the retrogasserian trigeminal root, respectively.
Methods: A total of 10 RFL procedures (5R, 5L), were performed on cadaveric specimens. Pre-procedural thin-cut CT scans were obtained and registered to the Medtronic Stealth S7 navigation system. Using data obtained from the neuronavigation unit, we measured (1) the distance from site of entry to FO, (2) the distance from FO to the clival line, and (3) the associated coronal and sagittal trajectory angles. We then assessed the modified Tew hypothesis that V3 could be accessed using a curved electrode (laterally) at the clival line, V2 could be accessed using a curved electrode (medially) at the clival line, and that V1 could be accessed using a curved electrode (medially) 5 mm distal to the clival line.
Results: The mean distance between the percutaneous entry point and FO was 7.603 cm ± 0.546cm. The mean distance between the FO and the clival line was 12.74mm ± 1.05mm. The mean angle between our planned trajectory and a mid-sagittal line was 21.95° ± 6.89°. The mean angle with respect to the palatal line was 49.58° ± 6.42°. Successful contact was made with V3, V2, and V1 in 10/10, 9/10, and 8/10 attempts, respectively.
Conclusion: This study confirms the feasibility of neuronavigation-assisted percutaneous RFL and offers useful morphometric guidelines including key distances and angles to successfully reach FO and selectively access V1, V2, or V3 fibers. We encourage the development of a Tew electrode that is compatible with current neuronavigation software. Future clinical studies will be needed to confirm the validity of these guidelines.