Development of the anterior chordal canal.

Resent advances have led to the reexamination of the intraosseous pathway of the chorda tympani a few years ago and they stated that the nerve never enters the mandibular fossa and its exit the skull base in the sphenopetrosal fissure. In our report, 58 temporal bones were investigated after maceration and formalin fixation in order to understand the development of the anterior chordal canal. Our study revealed that the chorda tympani leaves the tympanic cavity through the tympanosquamosal fissure before formation of the anterior chordal canal of Huguier. This canal is situated parallel to and in front of the musculotubal canal and formed by the processus inferior tegminis tympani and the sphenoid bone between the second and fifth years of age. Prior to the age of 2, only the exit of the bony canal exists which is gradually followed by the appearance of a groove in the growing processus inferior tegminis tympani. The borders of the groove elevate and develop to upper and lower plates which lengthen with similar plates of the sphenoid bone, completing the anterior chordal canal by the fifth postnatal year. The entrance of the canal develops above the petrotympanic fissure and similar to the canal itself, it is also completely formed in the fifth year. In case of an incomplete development the anterior chordal canal remains partially opened laterally which might allow the head of the mandibula to effect the chorda tympani mechanically causing Costen's syndrome.