Improved auditory performance of cochlear implant patients using the middle fossa approach

The preliminary results of insertion of a cochlear implant via the middle f ossa in nine patients with profound bilateral hearing loss are described. A etiologies included a bilateral radical mastoidectomy cavity, adhesive otit is media, autoimmune inner ear disease, previous cranial trauma, genetic pr e-lingual deafness, and otosclerosis, A classic middle fossa approach was adopted. A small cochleostomy measuring 1.5 mm in diameter was performed on the most superficial part of the basal turn. A Nucleus 24M cochlear implant system (Cochlear Corporation) was ins erted in four patients, a Lauraflex implant (Philips Hearing Implants) was used in three patients and a Combi 40+ (Med-el) with a double electrode arr ay in two. Single electrode arrays were inserted from the cochleostomy to t he cochlear apex and occupied a portion of the basal turn, as well as the m iddle and apical turns. Double electrode arrays were inserted, one towards the apex and one into the basal turn of the cochlea towards the round windo w. The receiver-stimulator was positioned in a bone well previously drilled in the temporal squama and the electrode carrier was inserted in the fenes trated cochlea. The activity of the inserted electrodes was tested by means of telemetry an d intraoperative recording of electrically evoked auditory brainstem respon ses (EABR). Speech recognition tests, performed over a period of time rangi ng from one to six months after cochlear implant activation, yielded better results in these patients compared with those obtained in postlingually de af patients operated on via the traditional transmastoid route. Cochlear im plant insertion via the middle fossa approach is a technique which is suita ble for the implantation of patients with bilateral radical mastoidectomy c avities, chronic middle ear disease, middle ear malformations, or with part ial obliteration of the cochlea in the basal turn. However, the main advantage of inserting the implant through the middle fos sa cochleostomy consists in the possibility of stimulating, with the single array, areas of the cochlea, i.e. part of the basal, middle and apical tur ns, where a greater survival rate of spiral ganglion cells is known to occu r. In addition, with the double array total occupation of the cochlea is po ssible, providing the possibility of replicating the tonotopic organization of the cochlea. This new approach has led to major improvements in speech recognition in al l patients compared with patients operated on via the transmastoid approach and, given the present state of the art, may be the elective approach for optimal implantation outcomes.