The potential applicability of facial nerve monitoring as a navigation tool in parotid gland surgery

Objectives: The aim of this study was to assess the relationship between the stimulation amplitude and the distance to the facial nerve. Methods: This study was designed as a prospective clinical study. A total of 20 patients (12 males, 8 females) were included. Partial superficial parotidectomy was performed in all patients with intraoperative facial monitoring. Measurements were made on the main trunk and major branches. Stimulation was started at 1 mA and incrementally increased to 2 and 3 mA's. The shortest distance creating a robust response (>100 mV) was recorded. Results: At 1 mA, 2 mA and 3 mA stimulation intensity, the average distance between the tip of the stimulation probe and the main trunk was 2.20 +/- 0.76 mm (range 1-3 mm), 3.80 +/- 0.95 mm (range 2-5 mm), 4.80 +/- 1.05 mm (range 3-7 mm) respectively. The stimulus intensity was inversely proportional in respect to the distance between the nerve and the tip of the stimulus probe (P <.00). The same relation was present in the facial nerve major branch measurements (P <.00). Conclusion: The proportional stimulation amplitude and distance to the facial nerve is thought to be a reliable auxillary method to assist the surgeon by facilitating the estimation of the distance to the facial nerve during extracapsular dissection and minimally invasive cases where the facial nerve isn't routinely dissected. Level of evidence: Level 3. (c) 2022 Associacao Brasileira de Otorrinolaringologia e Cirurgia Cervico-Facial. Published by Elsevier Editora Ltda.