Topographic relationship between the cochlea and the middle fossa floor: the anatomical basis for an alternative approach to the cochlear turns

The cochlea has attained extreme surgical interest since cochlear implantation has been recognized as an established method for the management of certain types of bilateral profound hearing loss. Traditionally access to the cochlear turns is achieved through the middle ear. Extremely limited references exist in the literature regarding alternative surgical approaches to the cochlea. In the present study we tried to highlight the anatomic relationships of the superior aspect of the bony cochlea to the adjacent superficial structures of the petrous bone, as there have been suggestions that the cochlea is surgically accessible through the floor of the middle cranial fossa (MCF). A total of 58 dry human adult skulls (116 temporal bones) were studied. The groove for the greater superficial petrosal nerve (GGSPN) and the facial hiatus were used as landmarks in order to expose the superior aspect of the cochlea. Measurements were made of the following distances: a) between the MCF floor and the superficial part of the basal turn (SPBT), b) between the MCF floor and the apex of the cochlea, c) between the SPBT and the GGSPN and d) between the SPBT medially and the first genu of the facial canal laterally. Our results indicate that adequate and reliable surgical access to the bony cochlea could be achieved through the MCF floor.