Preoperative imaging of the inner ear prior to the implantation of a multichannel cochlear implant using computed and MR tomography

CT and MRT are now standard examinations prior to insertion of a cochlear i mplant. Both methods have advantages and disadvantages in terms of discover ing potentially pathological structures in the inner ear. The aim of this s tudy was to evaluate the pros and cons of using CT and MRT before cochlear implantation. CT is usually performed using axial planigraphic planes. Like MRT, bone-spe cific CT is helpful in the diagnosis of congenital and acquired changes wit hin the inner ear. Congenital defects in the meatus acusticus internus, the endolymphatic duct and sac, the cochlea and the vestibulum can be diagnose d and also quantified. Infectious morphologic changes can be seen on CT ima ges in their terminal residual state (sclerotic tissue). However, acute inf lammation and fibrotic tissue is not visible on CT. T2-specific MRT images are very fluid sensitive and play a major role in preoperative cochlear imp lant diagnosis. This examination demonstrates fluid within the peri- and en olymphatic cave and permits the diagnostician to determine whether congenit al or acquired diseases have destroyed such fluid-filled cavities. In order to demonstrate pathological changes in the temporal bone and neural struct ures-in the inner ear, MRT is the preferred method. Displaying the modiolus and the cochlear nerve is extremely important because, in their absence, a cochlear implantation may be contra-indicated. MRT also demonstrates other neural structures such as the facial nerve. This information may be import ant for the surgeon, e.g. the state of the pneumatic system in the mastoid cavity (which is best visualised by bone-specific CT).