Initial, or fenestral, otosclerosis occurs in the area of the fissula ante fenestram
, a vestigial embryonic cleft anterior to the oval window and stapes, and typically progress to involve the cochlear promontory, vestibule and otic capsule.
(4) When the anterior part of the oval window, the fissula ante fenestram
, is involved there can be extension to the annular ligament and the stapes, causing bony ankylosis of the stapes and increased stiffness of the ossicular chain and resulting in conductive hearing loss.
The underlying pathologic processes involved in otosclerosis can affect various parts of the otic capsule, but the fissula ante fenestram is the most commonly involved area.
Subsequently, the size of this hypodense area was evaluated using a polygonal ROI program that allowed assessment of its borders in the fissula ante fenestram within an oval ROI.
Computed tomography (CT) was performed, revealing demineralization at the fissula ante fenestram bilaterally (figure 2).
CT demonstrates demineralization at the fissula ante fenestram demonstrates a reddish blush on the cochlear promontory.
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).'  In the lytic phase, the oval window can appear to be too wide on computed tomography (CT) as a result of the osteoclastic resorption of its margins (figure).
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 ante fenestram.  In this article, we report a case of pneumolabyrinth secondary to perilymphatic fistula, which was verified on surgical exploration.
 He defined implosive forces as those that cause pressure changes in the middle ear space and thus exert an external force on the oval and round window membranes, the fissula ante fenestram, the microfissures, and Hyrtl's fissure.