Pre-operative imaging for cochlear implantation: magnetic resonance imaging, computed tomography, or both?

Previous studies of computed tomography (CT) and magnetic resonance imaging (MRI) before cochlear implantation have been of limited sample size, lacked statistical analysis, and been inconsistent in their conclusions. We aim to quantify the utility of CT, MRI, and their combination in order to rationalize their selection.

Clinical records and radiological findings were correlated retrospectively in 158 adults and children. All underwent both CT and MRI.

A total of 27.9% (95% confidence interval (CI): 21.0-35.5) of patients had a significant radiological abnormality, but these were considered critical to subsequent management in only 12.7% (7.9-18.9). All these were detected by MRI. They were missed by CT in 6.3% (3.1-11.3). In all, 6.3% also had non-critical abnormalities that were reported only on CT. Cochlear dysmorphisms were more common in children but the overall frequency of abnormalities and their detection rates did not depend on age. Omitting CT and using MRI alone are estimated to miss no critical abnormalities (95% CI: 0-2.3 %).

While CT may be better at defining some abnormalities, MRI appears to be able to detect all abnormalities that are critical to patient management. Most candidates for cochlear implantation can therefore be assessed by MRI initially. CT is most likely to be helpful in those with a history of severe middle ear disease, meningitis, or dysmorphic syndromes, who should undergo both CT and MRI.