Utilization of the Tympanomastoid Fissure for Intraoperative Identification of the Facial Nerve: A Cadaver Study

Purpose Intraoperative identification of the facial nerve is an essential component of parotid gland surgery. Failure to visualize the facial nerve during the procedure can result in significant complications such as facial palsy. Several anatomic landmarks are used clinically to identify the facial nerve trunk; however, most of these structures have variable locations with respect to the nerve. The tympanomastoid fissure is the closest and least variable of the anatomic landmarks used in parotid gland surgery. The aim of this study was to evaluate the distance between the tympanomastoid fissure and the facial nerve trunk. Materials and Methods Thirty cadaver sides were dissected. A modified Blair incision exposed the facial nerve trunk, and the dissection was extended to the stylomastoid foramen and adjacent mastoid process. The distance between the most lateral aspect of the tympanomastoid fissure and facial nerve trunk was obtained using a digital caliper. Results The distance from the tympanomastoid fissure to the facial nerve trunk ranged from 3.3 to 9.2 mm with a mean of 4.9 mm. Conclusions The results showed that the tympanomastoid fissure is a close and predictable anatomic landmark that can be used to identify the facial nerve trunk intraoperatively.