The mechanisms responsible for ossification in labyrinthitis ossificans (LO) have not been fully elucidated. While LO can result from otosclerosis or cochlear trauma, it usually is the sequela of suppurative labyrithitis, either through meningitis, hematogenous spread to the labyrinth, or from spread of middle ear infection to the labyrinth. The spread to the ear from meningitis is presumed to occur via the cochlear aqueduct and thus affects the basal turn of the cochlea most often. Once infected, the labyrinth proceeds through a healing process that can lead to fibrosis and/or bone growth in the labyrinth. In animals, fibrosis can occur as early as 2 weeks following labyrinthitis and ossification as early as 2 months.
The fibrosis and ossification doen not seem confined to one structure, such as the basilar membrane. Although I was unable to find a specific reference to support this, my impression is that in LO from meningitis the scala tympani is more severely affected than the scala vestibuli since in cochlear implant cases I often find a patent scala vestibuli even when the scala tympani seems extensively ossified. I imagine that this is due to the fact that the cochlear aqueduct terminates in the scala tympani near the round window.