Congenital cerebrospinal fluid fistulae of the petrous temporal bone.

Spontaneous cerebrospinal fluid fistulae from the subarachnoid space into the middle ear cavity may be classified as perilabyrinthine or translabyrinthine. The very rare perilabyrinthine group, through bony defects close to but not involving the labyrinth, usually have normal hearing initially. The commoner translabyrinthine group are nearly always associated with anacusis, severe labyrinthine dysplasia and a route via the internal auditory meatus. The labyrinthine deformity is more severe than the type classically described by Mondini, and evidence of a dilated cochlear aqueduct in these cases is also unconvincing.