Auditory outcomes in tumor vs. nontumor patients fitted with auditory brainstem implants

Auditory brainstem implants (ABIs) are currently indicated for patients older than 12 years with neurofibromatosis type 2 (NF2) who had bilateral schwannoma removed. Over the last 10 years, we have extended the indications for ABIs to nontumor children and adult patients with cochlear or cochlear nerve injuries or malfunctions who would not benefit from a cochlear implant. We have provided ABIs for patients with cochlear nerve aplasia and other injuries, and patients in whom any benefit was, or would be, severely compromised as in extensive cochlear ossification. In the present chapter we report our recent findings in adult ABI patients and compare the psychophysical and speech perception outcomes in tumor with those in nontumor patients. We demonstrate that the ABI can stimulate the central auditory system in a way that gives the ability of open set speech understanding, and can thus be indicated in nontumor adult patients who are not candidates for a cochlear implant. From April 1997 to January 2006, a total of 80 patients, 62 adults and 18 children, were fitted with ABIs in the University of Verona ENT Department; age ranged from 14 months to 70 years. Twenty-six patients had NF2 with bilateral vestibular schwannoma removal, and 54 had nontumor diseases of the cochlear nerve or cochlea. The retrosigmoid approach was used in all patients. All patients had a functioning implantation, and no complications were observed during the operation, activation as well as long-term use of the ABI. All patients, except 1 (NF2), reported auditory sensations with activation of various numbers of electrodes (from 5 to 21). Different electrodes elicited different pitch sensations. At 1 year after implantations nontumor adults scored from 12 to 100% in open set speech perception tests (average 59%), and tumor (NF2) patients scored from 5 to 30% (average of 11%). The differences between these results are statistically significantly (p < 0.01). To investigate the cause of the differences in performance between tumor and nontumor ABI recipients, a series of psychophysical tests were done consecutively in 39 adult patients with implants (25 nontumor and 14 tumor patients) from May 1999 to April 2004 and with a follow-up of at least 1 year. The outcome of this study shows that: (1) The ABIs allow most tumor and nontumor patients to experience improved communication as well as awareness of environmental sounds. (2) Nontumor patients had better hearing outcomes than tumor patients when the variation in the auditory benefit with the ABI in relation to the patient's underlying pathological conditions were taken into consideration. (3) A significant number of nontumor patients are able understand speech at a level comparable to that of the most successful cochlear implant users including conversational telephone use. (4) The ABI represents the tool for hearing rehabilitation in patients with profound hearing loss who cannot be fitted with cochlear implants.