Mediterr. J. Otol 2007; 3:(3) 133-139

Anatomic Considerations for Electrode Implantation into the Modiolus

Katya Assenova, Stefan Stoyanov, Todor Karchev

Ear, Nose, and Throat Department, Medical University of Sofia, Sofia, Bulgaria, dr.assenova@gmail.com 

OBJECTIVE: The aim of this study was to assess the anatomic factors that enable successful direct implantation of an electrode into the modiolus.

METHODS: We studied the topographic location of the modiolus, including its apical part, to determine an appropriate surgical approach. Ten dissections of human temporal bones were performed. We measured the distance between the apex of the cochlea and the floor of the middle cranial fossa. The length of the modiolar axis was also measured. We used stereomicroscopy to study the modiolus for the possible placement of an electrode along its axis. Finally, via a cochleostomy on the anterior pyramidal surface, we introduced an experimental electrode from the apex to the base of the modiolus, aiming to determine the appropriate length for a modiolar electrode.

RESULTS: We found that the appropriate surgical approach to the modiolus is through middle cranial fossa. The cupola (apex) of the cochlea is located medial and anterior to the ganglion geniculi. The greater petrosal nerve served as a landmark. The cupola is about 2 mm below the upper surface of the petrous bone. An 8- to 10-mm electrode can be implanted without causing severe damage to the nerve trunk. The results of histologic studies revealed modiolar anatomic structures in detail.

CONCLUSIONS: The results of our study suggest that the implantation of an electrode into the modiolus is possible. Modiolar implantation could be an alternative to standard cochlear implantation, especially in patients with severe cochlear ossification and cochlear or middle ear malformation.