Anatomical and Surgical Study to Evaluate the Accuracy of "C-M-S" Technique in Facial Nerve Identification During Parotid Surgery.

Facial nerve identification is considered to be a crucial step in parotid surgery as inadvertent injury to the nerve will lead to facial paralysis. Multiple landmarks are described in literature to identify the facial nerve during parotid surgery but controversies remain as the consistency and accuracy of these landmarks vary. Numerous studies exist in literature but they fail to address a single landmark that is most reliable to identify the facial nerve during parotid surgery. The purpose of this study is to find reliable landmarks for identification of the main trunk of facial nerve during parotid surgery by evidence gathered by cadaveric dissection and intraoperative study during parotid surgery and develop a systematic approach to identify the facial nerve trunk. This prospective study included 41 cadavers (82 parotid regions) and 20 patients with parotid pathology who underwent parotidectomy. We evaluated the feasibility of our C-M-S technique to identify the main trunk of facial nerve in both anatomical and surgical study. The relationship of landmarks (tragal pointer, tympanomastoid suture, superior border of posterior belly of digastric muscle) to the facial nerve trunk was assessed and the shortest distance between them from the facial trunk was measured using a slide caliper. The measurements were compared between the anatomical and surgical study. The main trunk of facial nerve was successfully identified in all cases using C-M-S technique in both anatomical and surgical study. Distance of facial nerve trunk to tragal pointer was more in the cadaveric sample (13.04 ± 5.238 mm) compared to live patients (9.95 ± 3.967 mm) with statistically significant difference  = 0.036). The mean distance of tympanomastoid suture and posterior belly of digastric muscle to the facial nerve trunk was similar in anatomical and surgical study with value of 0.877 and 0.083 respectively. The tympanomastoid suture, posterior belly of digastric muscle and tragal pointer are the most useful landmarks for facial nerve identification during parotid surgery. In our study we found that the tympanomastoid suture line is the most consistent landmark present in all our cases and being closest to the facial nerve trunk in both anatomical and surgical study. Further we recommend using the "C-M-S technique" in order to locate the main trunk of the facial nerve.