Congenital malformations of the ear and cochlear implantation in children:review and temporal bone report of common cavity

The objective of this review is to analyze aspects of congenital malformati on of the ear in relation to cochlear implantation in children. Having brie fly described the in utero development of the ear and the classification of types of external, middle and inner ear malformation, five practical aspec ts of these malformations are discussed. It seems likely that the combinati on of bilateral profound sensorineural deafness with bilateral microtia sev ere enough to make a surgical approach to the cochlea difficult will be ext remely uncommon. No such cases have been reported, although Klippel-Feil de formity seems the syndrome most likely to produce this set of circumstances . Abnormalities in the intratympanic course of the facial nerve have been ass ociated with cochlear malformation, emphasizing the benefit of intra-operat ive facial nerve monitoring, and a technique suggested for safely avoiding an abnormally placed nerve. Fistulae of cerebrospinal fluid (CSF) and peril ymph can complicate surgery and are relatively common in common cavity and Mondini malformations. Strategies for facilitating surgery in the presence of 'gushers', for measuring the pressure of a gusher and for placement of t he cochlear implant electrode array are reviewed, with reports of fluctuati ng levels of electric current when implants lie in dysplastic cochleas. The relationship of implant performance to VIIIth nerve tissue in malformed cochleas is discussed, with a description of the histological findings in a common cavity cochlea. Techniques for identifying the absence of the coch lear nerve are reviewed. Stimulation of the facial nerve by cochlear implan ts has been described in cases of congenital malformation of the labyrinth but is relatively uncommon. Case reports of the benefit received by implant ed children with congenital cochlear malformation have appeared since 1988. Most cases reported have not yet been followed for long enough to establis h a clear picture of the outcome following cochlear implantation in such ch ildren; no centre has yet built up a large series of cases, but there have been two multicentre postal surveys. It seems likely that in cochlear malfo rmation the range of potential outcomes in terms of hearing threshold and t he development of speech perception and production will be similar to the r ange found in implanted children without cochlear dysplasia. However there is, as yet, no clear picture of the mean level of performance within this r ange.