Abnormalities of the Facial Nerve in Temporal Bones With Inner Ear Malformations.

Background: Bony inner ear malformations (IEMFs) account for ~20% of congenital sensorineural hearing loss, often requiring cochlear or auditory brainstem implants. To ensure safe cochlear implantation in patients with IEMFs, understanding their anatomical features, particularly related to the facial nerve (FN), is crucial. Methods: We examined 28 TBs obtained from donors with bony IEMFs. We classified cochlear and vestibular malformations and analyzed several anatomical features, including the diameter of the internal auditory canal (IAC), the angle of the first genu, the relationship of FN with the oval window (OW), the facial recess (FR), and the overall development of the FN. Results: Among the TBs, 5 (17.8%) were cochlear hypoplasia-type II, 20 (71.4%) were cochlear hypoplasia-type III, 2 (7.1%) were incomplete partition-type II, and 1 (3.5%) had an isolated vestibular malformation. The IAC diameter was narrow in 2 of 26 TBs (7.7%). The first genu angle was obtuse or perpendicular in 14 of 20 TBs (70.0%). The FN was abnormally located in 8 of 27 TBs (29.6%). The FR was narrow (< 2.5 mm) in 16 of 27 TBs (59.3%). Additionally, the FN was hypoplastic in 18 of 28 TBs (64.3%). Conclusion: Our study revealed a high prevalence of FN abnormalities among patients with IEMFs. Some of these abnormalities could pose significant challenges when using the traditional FR approach for cochlear implantation. Our findings underscore the importance of thoroughly evaluating the FN course preoperatively to mitigate the risks of surgical complications. Evidence Level: N/A.