Gd-DTPA-enhanced MR imaging of cochlear schwannoma.

The majority of eighth cranial nerve tumors are acoustic schwannomas, with greater than 90% arising from the vestibular division within the internal auditory canal. Most originate near the porus acusticus at the gliai-Schwann cell interface. The minority of vestibular schwannomas arise at other locations along the nerve, such as within the vestibule or at the fundus of the internal auditory canal. Schwannomas arising from the cochlear division in the absence of vestibular involvement or neurofibromatosis are rare. Previously, cochlear schwannomas have been seen primarily at autopsy, although demonstration by CT [1, 2] and polytomography [3] have been reported . CT evaluation of eighth cranial nerve tumors has largely been replaced by MR imaging. The recent availability of paramagnetic contrast agents has further enhanced the value of MR in the preoperative localization of intracanalicular or intralabyrinthine tumors [4] . The case reported here represents in vivo demonstration of an isolated cochlear schwannoma by means of paramagnetic-contrast-enhanced MR imaging. The ability to demonstrate the cochlear location of the abnormality had direct bearing on clinical management and surgical planning.