Facial nerve in parotidectomy: A topographical analysis

Objective: Establish normative data concerning parotidectomy and facial nerve dissection and determine the relationship between the length of the facial nerve dissected during parotidectomy and subsequent facial nerve paresis. Study Design: Prospective mapping of facial nerve during parotidectomy and comparison with postoperative facial nerve function. Methods: A prospective observational study of 78 patients who underwent 79 parotidectomy procedures. During each procedure, various topographical measurements were recorded. These measurements included the distance from the tragal pointer to the main trunk of the facial nerve, the distance to the pes anserinus, and length of each segmental branch dissected. In addition, a designation of the patient's tumor location was made by drawing a line from the ear canal to the nasal spine. Tumors above this line were designated anatomic zone A and those below the line were designated anatomic zone B. Finally, facial nerve function was quantified at a 1-week follow-up visit using the House-Brackmann Scale. Results: The distance from the main trunk of the facial nerve to the tragal pointer was significantly (P <.000) less than the previously accepted standard of 1 cm. The cervical and marginal mandibular branches had more nerve dissected, whereas the eye and forehead branches were the least dissected. Results of an independent t test and logistic regression (P =.01, both) indicated that patients with temporary facial nerve paresis had a significantly greater amount of nerve dissected than patients without temporary facial nerve paresis. Patients with short-term facial nerve dysfunction had significantly (P <.01) more total nerve dissected (136.73 mm vs. 94.73 mm) than patients without short-term facial nerve dysfunction. Patients with nerve dissection lengths at the third quartile (130.0 mm) were 3.8 times more likely to experience temporary facial nerve paresis than patients with nerve dissection lengths at the first quartile (64.5 mm). Conclusions: The axiom that the main trunk of the facial nerve is located 1 cm from the tragal pointer may need to be modified to less than 1 cm. The cervical and marginal mandibular branches had more nerve dissected, whereas the eye and forehead branches were the least dissected. Facial nerve paresis after parotidectomy is associated with the length of the facial nerve dissected during the procedure. The greater the length of facial nerve dissected, the higher the chance of facial nerve paresis, albeit temporarily, in this particular series of patients.