Temporal bone characterization and cochlear implant feasibility in the common marmoset (Callithrix jacchus)

The marmoset (Callithrix jacchus) is a valuable non-human primate model for studying behavioral and neural mechanisms related to vocal communication. It is also well suited for investigating neural mechanisms related to cochlear implants. The purpose of this study was to characterize marmoset temporal bone anatomy and investigate the feasibility of implanting a multi-channel intracochlear electrode into the marmoset scala tympani. Micro computed tomography (microCT) was used to create high-resolution images of marmoset temporal bones. Cochlear fluid spaces, middle ear ossicles, semicircular canals and the surrounding temporal bone were reconstructed in three-dimensional space. Our results show that the marmoset cochlea is similar to 16.5 mm in length and has similar to 2.8 turns. The cross-sectional area of the scala tympani is greatest (similar to 0.8 mm(2)) at similar to 1.75 mm from the base of the scala, reduces to similar to 0.4 mm(2) at 5 mm from the base, and decreases at a constant rate for the remaining length. Interestingly, this length area profile, when scaled 2.5 times, is similar to the scala tympani of the human cochlea. Given these dimensions, a compatible multi-channel implant electrode was identified. In a cadaveric specimen, this electrode was inserted 3/4 turn into the scala tympani through a cochleostomy at similar to 1 mm apical to the round window. The depth of the most apical electrode band was similar to 8 mm. Our study provides detailed structural anatomy data for the middle and inner ear of the marmoset, and suggests the potential of the marmoset as a new non-human primate model for cochlear implant research. (c) 2012 Elsevier B.V. All rights reserved.