Fenestral Otosclerosis

Fenestral otosclerosis/otospongiosis is abnormal lucency at the fissula ante fenestram (a cleft of fibrocartilaginous tissue between inner & middle ears just anterior to oval window).

Bone algorithm CT will show relatively lucent foci at anterior margin of the oval window (black arrow). Late findings during the healing phase include new bone along oval and round window margins. The anterior (blue) and posterior (red) crura of the stapes are indicated in the oval window. The bottom image is from a normal subject.