CT petrous temporal bone with an axial plane parallel to the lateral semicircular canal. The important key structures at this level include the three ossicles (from anterior to posterior: malleus manubrium, incus long process and stapes crura), vestibule, footplate of the stapes in the oval window, cochlea (apical turn) and vestibular aqueduct.  The illustration shows the fissula ante fenestram, the bony labyrinth and the space for the membranous labyrinth. The fissula ante fenestram located at the lateral wall of the vestibule (anterior to the oval window) and it stands parallel to the adjacent cochlear turn. Any curvilinear lucency at the fissula ante fenestram, should be considered as possible "fenestral otosclerosis" in adult, and "cochlear cleft" should be excluded in the pediatric age group.