POSTOPERATIVE RADIOGRAPHIC ASSESSMENT OF THE COMBI-40 COCHLEAR IMPLANT

OBJECTIVE. The aims of this study were to establish a plain radiograph ic technique for the assessment of the postoperative appearance, posit ion, and insertion depth of the Combi 40 cochlear implant and to corre late the radiologic findings with surgical reports. SUBJECTS AND METHO DS. In an experimental study, an electrode of the Combi 40 device was inserted into the cochlea of a cadaveric skull. Digital radiographs we re obtained in a modified Chausse III projection, in which the skull w as placed supine on the radiography table with the infraorbitomeatal l ine strictly perpendicular to the film cassette, The skull was then ro tated 30 degrees away from the side to be examined, and the central X- ray beam was angled 15 degrees cephalad to the infraorbitomeatal line. On these radiographs, the point of cochleostomy was marked by a needl e tip and was projected inferior to the vestibule and on a line drawn through the superior semicircular canal and the vestibule. The appeara nce and position of the electrode was evaluated. An electrode was defi ned as completely inserted if all electrode contacts projected medial to the line drawn through the superior semicircular canal and the vest ibule. We also studied cochlear implant insertion of the Combi 40 devi ce in 37 patients. Postoperative digital radiographs of these patients were obtained and analyzed for the criteria as defined in the cadaver ic study, In addition, the insertion depth of the electrode and the an gle of insertion were measured on the radiographs. This depth was corr elated with depth of insertion as estimated at surgery. RESULTS. The c adaveric study showed that the completely inserted electrode was seen on radiographs as a nonoverlapping spiral within the cochlea. All elec trode contacts projected medial to the line drawn through the superior semicircular canal and the vestibule. Tn all 37 patients, the electro de could be seen without overlapping. According to our criteria, a com pletely inserted electrode was seen in 32 patients. In these patients, the insertion depth ranged from 21 to 34 mm and the angle of insertio n ranged from 350 degrees to 810 degrees, In two patients, we saw a co mpletely inserted electrode with a bend, In three patients, an incompl etely inserted electrode was seen. Excellent correlation existed betwe en the radiologic and surgical results with regard to insertion depth (r = .92). CONCLUSION. Digital radiographs obtained in the modified Ch ausse III projection allow clear depiction of the electrode and avoid overlapping. Such radiographs enable a reliable and accurate assessmen t of the position and insertion depth of the electrode of this new coc hlear implant. Such images can serve as a baseline for further radiogr aphic examinations when extrusion or slippage of the electrode is clin ically suspected.