Abstract
A considerable proportion of the candidates for multichannel cochlear implantation consists of patients with profound bilateral hearing loss caused by sclerosing and/or ossifying labyrinthitis as a complication of meningitis. The spread of bacteria and viruses from the meninges to the inner ear is generally thought to be either via the subarachnoid sheaths following the nerves in the internal acoustic canal, or more directly through the cochlear aqueduct. The infective stage can be followed by fibrosis of the labyrinth and later by new bone formation which may proceed to almost complete obliteration of the labyrinth.
Computed tomography remains the first examination to perform in order to have a precise map of the inner ear and temporal bone anatomy as well as to depict any abnormality of the round window or calcification of the membranous labyrinth. In many centres CT is the first imaging modality chosen in the evaluation of cochlear-implant candidates, providing higher spatial resolution and unique information on skeletal structures. Temporal bone MR examination adds useful information before surgery because only thin T2-weighted sequences may depict focal or diffuse obliteration of the membranous labyrinth fluid space before calcification with a high degree of sensitivity.
Moreover, MR plays a role in planning surgery, because a remaining postmeningitis labyrinthitis enhancement seems to predict a rapid evolution towards labyrinthine calcification.
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