Surgical anatomy of the chorda tympani: a micro-CT study

Purpose

Iatrogenic injury of the chorda tympani is a well-known complication of middle ear surgery, yet few studies have investigated the intraosseous course of the nerve. The aim of this study was to accurately delineate the posterior canaliculus in the temporal bone, particularly its relationship to the tympanic annulus, which is critical during the insertion of subannular ventilation tubes.

Methods

Forty temporal bones from 27 cadavers (15 male, mean age 75?years, 13 bilateral) were scanned using a micro-CT scanner, and standardised 3-D multiplanar reconstructions were generated using a software platform. The posterior canaliculus was measured in relation to reproducible bony landmarks.

Results

In 6 (15%) specimens, the chorda tympani originated from the facial nerve outside the skull and in 34 (85%) from within the facial canal at a mean of 3.2?±?1.8?mm above the stylomastoid foramen. The posterior canaliculus was 12.3?±?3.8?mm long and converged on the tympanic sulcus cranially. It entered the middle ear at 62?±?10% of the height of the tympanic membrane.

Conclusions

This novel micro-CT study defines the precise anatomy of the posterior canaliculus housing the chorda tympani and provides data that may help the otologic surgeon protect the nerve from iatrogenic injury.