Cochlear implant surgery in challenging cases
Expanding selection criteria and increasing numbers of cochlear implantations have revealed several challenging cases with regard to surgery and medical point of view. Cochlear implantation of congenitally deaf children with inner-ear malformations may involve difficulties in preoperative evaluation, surgical approach and postoperative follow-up. Cochlear nerve aplasia (as evidence of only one existing nerve in three dimensional magnetic resonance imaging) and hypoplastic cochleas are among the most difficult cases and sometimes children are considered unsuitable for cochlear implantation. However, there is always the possibility that hypoplastic cochleas may include ganglion cells and the only nerve in the internal auditory canal (facial nerve) may contain auditory fibres as well. A positive history of auditory experience and evidence of electrical auditory brainstem response or response to the promontory or round window electrical stimulation may imply that a functioning auditory system is in place. Malformations like common cavity deformity, isolated bilateral vestibular aqueduct enlargement and Mondini dysplasia are usually less challenging, although cerebrospinal fluid leak and postoperative meningitis may be a possibility. In cases of post-meningitic deaf patients, ossification (or obliteration) may be a serious problem even if computed tomography and MRI scan show a patent cochlea or minimal changes. Acoustic neuromas and neurofibromatosis type 2 are other challenging cases, as there is always the possibility that the sensorineural hearing loss is secondary to cochlear damage by interference of the tumour to cochlear blood supply. In conclusion, challenging cases are becoming more common as we are expanding selection criteria, and we should be prepared for alternative cochlear implant devices (straight electrode arrays, dual arrays, compressed arrays, etc.), increased rate of possible complications at, and following, surgery, and functional outcome that may vary considerably among implantees.