Patterns of anomalies of structures of the middle ear and the facial nerve as revealed in newborn temporal bones.

HYPOTHESIS: The purpose of this study is to offer new data about facial nerve malformations in the tympanic cavity.

BACKGROUND: Prospective anatomic study of newborns to demonstrate the submacroscopic anatomy of the intratympanic facial nerve and its surrounding structures by malformations.

METHODS: Step-by-step microdissection of 12 newborn temporal bones and histologic evaluation of 4 middle ears showing multiple malformations.

RESULTS: Four of 12 temporal bones presented malformation in the middle ear. All 4 temporal bones showed developmental failures of the stapes, and 3 of them had malposition of the tympanic portion of the facial nerve. In 3 cases, there was an oval window atresia, and in 1 case, the rim of the oval window was not ossified and was positioned medial to the stapes.

CONCLUSION: Malformation or displacement of the stapes can be an indirect sign for facial nerve malformation. The most common site for facial nerve malformation is the tympanic portion. The tympanic segment of the nerve is devoid of bony covering in association with these anomalies of the stapes.