**4. Facial nerve and chorda tympani nerve palsy**

Facial nerve palsy and chorda tympani are also known to occur in some cases of congenital microtia. In our study [5], facial nerve paralysis (House-Brackmann grade more than III) and change in taste detection threshold due to chorda tympani nerve dysfunction were found in 8 and 10% of patients with microtia, respectively. We found that chorda tympani nerve dysfunction did not correlate significantly with the anatomic structure of the ear anomalies based on Jahrsdoerfer scores. On the other hand, facial nerve paralysis was significantly correlated with the presence of a malleus-incus complex, a pneumatized mastoid, an incus-stapes connection, and an external auditory canal, and facial nerve paralysis patients had a higher Jahrsdoerfer score than the chorda tympani nerve dysfunction patients.

The facial nerve canal arises initially as a sulcus in the cartilaginous otic capsule, and ossification begins from two distinct sites, such as anteriorly near the apex of the cochlea and posteriorly at the pyramidal eminence, at 20 and 25 weeks' gestation, respectively. The bone progressively covers the facial nerve, and the process is usually complete by 3 months after birth. Since the mastoid process and tympanic ring grow after birth, they displace the nerve medially. Therefore, the development of the facial nerve is closely related to the development of the middle ear and the mastoid process. Meanwhile, the chorda tympani branches from the facial nerve at 5 weeks' gestation and subsequently separates the stapes primordium and the incus primordium from the hyoid visceral bar. Unlike the facial nerve, the chorda tympani in the middle ear is not encased by a bony wall. This early branching and development of the chorda tympani may be one of the reasons why our study did not show a significant correlation between chorda tympani nerve dysfunction and facial nerve paralysis; 83% of patients with chorda tympani nerve dysfunction did not have facial nerve paralysis. In addition, there was no significant difference in Jahrsdoerfer scores for the facial nerve between those with and without chorda tympani nerve dysfunction [5]. It is speculated that facial nerve paralysis, probably including chorda tympani nerve dysfunction, does not always correspond to an anatomic abnormality of the nerve tract.
