Two cases of congenital stapes malformation: Implications for development of the stapes footplate and the oval window

The origin of the stapes footplate has been controversial for decades, especially regarding involvement of the otic capsule in the development of the footplate. We report two cases of stapes malformation in which the stapes footplate was absent, while the oval window was formed but was covered with mucosal membrane. Both the patients visited our department for long-standing hearing loss, which was due to congenital ossicular anomalies of rare variation, as suggested by intraoperative findings. Through two operated cases, we have also discussed the origin and the mechanisms in the development of the stapes and the oval window. The findings suggest that the formation of the oval window is independent from the development of the stapes footplate. Further reports and accumulation of cases with ossicular malformation are required to develop an appropriate classification of congenital ossicular anomalies based on both developmental mechanisms and analyses of the surgical outcomes.