Topographical Anatomy of the Chorda Tympani Nerve

Abstract

The topographical anatomy of the chorda tympani nerve (CTn) was investigated macroscopically in 45 ears of Japanese adult cadavers, aged 38~88 yr, with special reference to its topographical relationship to critical structures encountered in otorhinolaryngological practice such as the auditory tube and Wharton's duct. Fifteen cases of the “separated type” of CTn running independently along the posterior margin of the lingual nerve, which were noted in our previous study, were included among the 45 specimens. Major findings considered relevant to clinical practice are described below. 1. The course of the CTn, passing inferiorly and medially in the petrotympanic fissure, was classified into 2 types: that traveling immediately anterior to and parallel with the auditory tube, and the becoming progressively more distant (inferior and anterior) to the auditory tube. 2. Immediately after emerging from the petrotympanic fissure, the CTn consistently communicated with the sympathetic plexus around the middle meningeal artery, and often issued twigs reaching the otic ganglion area. 3. In cases where the CTn was trapped by tendinous tissue around the lateral pterygoid muscle (17.8%), the nerve merged into the lingual nerve from the medial or anterior aspect, and not from the usual posterior aspect, at the level of the mandibular notch. 4. The lingual nerve sometimes (20.0%) showed a strongly curved sigmoid course behind the mandibular ramus. Several buccal branches innervating the oral lining, without containing the CTn element, were issued at the anterior projecting protion of the sigmoid course. 5. At the base of the oral cavity, the major CTn element traveled along the superior margin of the lingual nerve, therefore the CTn element was located away from the submandibular ganglion. 6. A thick communicating branch on both sides of the lingual nerve was rarely observed under the mucous lining or in the mucous layers at the tip of the tongue. These findings suggest that morphological variations of the CTn should be considered during surgical procedures and for understanding the nature of related clinical symptoms. © 1995, The Society of Practical Otolaryngology. All rights reserved.