• SouHyun Lee, JiHee Hong, and HyeRa Jung.
• Department of Anesthesiology and Pain Medicine, Keimyung University School of Medicine, Daegu, South Korea.
• Pain Physician. 2021 May 1; 24 (3): E341-E348.

BackgroundRadiofrequency thermal rhizotomy demonstrates an excellent treatment outcome with a high success rate among patients of intractable trigeminal neuralgia. The triangular plexus which is an immediate retrogasserian portion of the trigeminal root is suggested as the best place of lesioning during radiofrequency thermal rhizotomy. However, the anatomy of the triangular plexus has been relatively unrecognized, while the anatomical study related to therapeutic procedure is scarce.ObjectiveThe purpose of this study is to confirm with gross and microscopic finding of the trigeminal system whether, if an electrode tip is placed on the petroclival junction in lateral cranial view, it actually arrives at the triangular plexus or not. In relation to therapeutic procedure, we examined the triangular plexus with morphological and histological methods.Study DesignHuman cadaveric study.SettingAn anatomical laboratory in South Korea.MethodsPercutaneous procedure of radiofrequency thermal rhizotomy under C-arm guidance was performed in 8 cadavers. Final target of the electrode tip was the petroclival junction under true lateral cranial view. The location of the electrode tip was determined under observation of the presence of an injected dye. Triangular plexus size was measured grossly and microscopically. Gross and microscopic evaluation of the triangular plexus was performed.ResultsAmong 15 trigeminal systems, 8 showed dye appearance in the triangular plexus, while 6 showed it in the trigeminal ganglion. Overall, 53% of radiofrequency thermal rhizotomy could reach the triangular plexus when an electrode tip was placed on the petroclival junction. The grossly measured average triangular plexus vertical and transverse diameters were 0.8 cm and 1.3 cm, respectively.LimitationOnly radiologic landmark was used to confirm the location of the electrode tip. However, further study confirming the location of the electrode tip under the guidance of electrical stimulation is needed.ConclusionWhen an electrode tip was placed on the petroclival junction, 53% of radiofrequency thermal rhizotomy could reach the triangular plexus.

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