Otospongiosis commonly begins at the fissula antefenestrum, a cleft of fibrocartilaginous tissue just anterior to the oval window.
The fenestral form will demonstrate a focal lytic plaque in the region of the fissula antefenestrum (Figure 16A).
The otosclerotic focus extended from the labyrinthine capsule through the fissula ante fenestram and into the round window niche (figure).
On the left side, the otosclerotic focus extended from the labyrinthine capsule, through the fissula ante fenestram, and into the round window niche.
Fenestral otoscierosis is the more common type, and it is thought to begin in the fissula
ante fenestram (anterior oval window margin).
Potential sites of gas entry include the oval and round window niche, microfissures between the posterior semicircular canal and the round window, and the fissula