Abstract
OBJECTIVE: To observe and summarize variations of the chorda tympani nerve to effectively protect it during surgery. METHODS: Surgical videos of patients undergoing endoscopic ear surgery in the past 3 years were retrospectively observed to identify chorda tympani nerve variations. RESULTS: In total, 237 cases were reviewed. The tympanic sulcus or annulus was the boundary between the posterior wall of the external auditory canal and chordal eminence (CE). The chorda tympani nerve was divided into three types: type I, the periannular segment was located medial to the CE and covered by the bony eminence (32.5%); type II, the periannular segment was located inferior to the CE, and the nerve did or did not contact the bony edge of the CE (62.0%); and type III, the periannular segment was located lateral to the CE and medial to the tympanic annulus, and the iter chorda posterius was located in the tympanic sulcus (5.5%). The rate of injury to the chorda tympani nerve was 2.5% of 237 cases. The location of the iter chorda posterius on preoperative computed tomography was highly reliable for prediction of type I and III nerves. Secondary exposure of the posterior canaliculus might occur in patients with external auditory canal cholesteatoma, who were specifically included in this study. CONCLUSION: CE-based classification of the chorda tympani nerve can concisely describe variations of the chorda tympani nerve and provide guidance for neuroprotection during endoscopic ear surgery. Patients with external auditory canal cholesteatoma may have secondary exposure of the posterior canaliculus. LEVEL OF EVIDENCE: NA.