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. 2022 Jun 17;7(4):1107-1112.
doi: 10.1002/lio2.838. eCollection 2022 Aug.

Variation and protection of the chorda tympani nerve in endoscopic ear surgery

Li Quancheng  1 , Zhong Jiangtao  1 , Chai Liang  1
Affiliations

Variation and protection of the chorda tympani nerve in endoscopic ear surgery

Li Quancheng et al. Laryngoscope Investig Otolaryngol. .

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.

Keywords: chorda tympani nerve; chordal eminence; classification.

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Conflict of interest statement

The authors declare no conflicts of interest in this research.

Figures

FIGURE 1
FIGURE 1
Adjacent anatomical relationship of CE and TS. (A, B) The TS was the boundary between the posterior wall of the bEAC and the CE. bEAC, bony external auditory canal; CE, chordal eminence; PTS, posterior tympanic spine; TA, tympanic annulus; TS, tympanic sulcus
FIGURE 2
FIGURE 2
Classification of the chorda tympani nerve based on chordal eminence. Type I, the periannular segment was (A) located medial to the chordal eminence and (B, C) covered by the bony eminence. Type II, (D) the periannular segment was located inferior to the chordal eminence, and the nerve either (E) did or (F) did not contact the bony edge of the chordal eminence. Type III, (G) the periannular segment was located lateral to the chordal eminence and medial to the tympanic annulus, and (H, I) the iter chorda posterius was located in the tympanic sulcus
FIGURE 3
FIGURE 3
Location of the iter chorda posterius. Preoperative computed tomography showed that the iter chorda posterius could be located (A) medial, (B) inferior, or (C) lateral to the chordal eminence. Yellow arrow, facial nerve; blue arrow, iter chorda posterius; red arrow, chordal eminence
FIGURE 4
FIGURE 4
Secondary exposure of the PC in a patient with tympanic perforation secondary to external auditory canal cholesteatoma. Computed tomography indicated that (A, B) the bony external auditory canal was enlarged and that (B) the PC was partially exposed below the meatal flap. (C) During the endoscopic tympanoplasty, the chorda tympani nerve could be identified from the exposed PC to the ICP. Yellow arrow, facial nerve; blue arrow, chorda tympani nerve. ICP, iter chorda posterius; PC, posterior canaliculus
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