C. Czerny et al., POSTOPERATIVE RADIOGRAPHIC ASSESSMENT OF THE COMBI-40 COCHLEAR IMPLANT, American journal of roentgenology, 169(6), 1997, pp. 1689-1694
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.