Learning Objectives: A systematic review to assess the radiological and histological evidence of cochlear trauma following cochlear implant insertion.

Introduction: Cochlear implantation (CI) has developed from its origins in the 1980s. Initially, CI was for profound bilateral hearing impairment. However, as candidacy for CI has become more relaxed, there is an increasing emphasis on hearing preservation.

Evidence supports the position that full electrode insertion in an atraumatic fashion into the scala tympani (ST) provides optimal hearing outcomes (Ashendorff et al 2005, Shepherd 1993, Finley et al 2008).

The main aim of this systematic review was to elucidate the degree of trauma associated with CI.

Methods: A systematic literature search was undertaken using PubMed Medline. A grading system described by Eshraghi (2003) was used to classify cochlear trauma. Both radiological and histological studies were included.

Results: Twenty one papers were identified which were relevant to our search. In total, 686 implants were inserted and 121 (17.6%) showed evidence of trauma. The cochleas with trauma had basilar membrane elevation in 10.5%, ruptured in 12.9%, the electrode passed from the ST to the scala vestibuli (SV) in 71.8% and there was grade 4 trauma consisting of spiral lamina or modiolus fracture and tear of the SV, in 4.8%.

The studies used a variety of histological and radiological methods to assess for evidence of trauma. A majority (57%) used histology either alone or with radiology (CT or x-ray). A majority of studies used cadaveric temporal bones (67%).

Conclusions: Minimising cochlear trauma during implant insertion is important to preserve residual hearing and optimise audiological performance. An overall 17.6% trauma rate suggests that CI could be improved with more accurate and consistent electrode insertion such as robotic guidance. The correlation of cochlear trauma with post-operative hearing has yet to be determined.