## 4 Discussion  
This study reports four cases of cochlear implant electrode array misplacement out of 355 CI procedures conducted in ears with normal anatomy. The malposition was diagnosed by the intraoperative plain radiographs, allowing reinsertion before terminating anesthesia. The objective of cochlear implantation surgery is complete insertion of the electrode array into the scala typpani with minimal trauma to cochlear partitions or nearby structures. Correct positioning of the electrode correlates with better audiologic function for the patient [12,13]. Overall, the reported incidence of electrode malposition (tip fold-over, extracochlear insertion, kinking, incomplete insertion) is \(<\)1%-5% [14,15] including cases with normal anatomy. Specifically, a tip fold-over incidence of 1.57% was found in a review of 13 articles, predominantly in the pre-curved cochlear implants [16]. The array misplacement incidence in our cohort of patients with normal anatomy was 1.1% with a tip fold-over incidence of 0.6%, corresponding with the published literature. The main purpose of intraoperative plain radiographs in cochlear implant surgery is to answer the question--is the electrode array correctly positioned inside the cochlea? The advantage of performing routine images in every surgery over selective imaging is demonstrated in a study which retrospectively compared intraoperative radiograph findings to the surgeon's impression of resistance during insertion as documented in the surgical report. It was found that the surgeon's suspicion of misplacement had only a 29% positive predictive value. Thus, if imaging had not been used for uneventful insertions, nearly half of the misplaced implants would have been overlooked [10]. When applying this to the four patients presented in this report, in cases 1, 2 and 4 (fold-overs and incomplete insertion) no abnormality or resistance during insertion was noticed, and only the performance of the routine intraoperative X-ray prevented misplacement. As for case 3, although some anatomic variation was noticed intraoperatively, the cochleostomy and insertion were uneventful and, again, if intraoperative radiographs had not been routinely used, chances are that imaging would not have been specially requested and the extracochlear position would have been missed. Case 3 also demonstrates a potential pitfall in pre-curved arrays regarding intraoperative imaging. Once the styled is removed, the pre-curved array coils into a spiral form even though it is positioned out of the cochlea [17]. As seen in Figure 3, the array actually curved to some degree despite not being in the cochlea, and a high index of suspicion was needed in order to detect the oval curvature and the acute-angle in the apex. The electrode was also not medial to the vestibule, which indicated a hypotympan placement. Neural response and impedance are standard intraoperative electrophysiological tests for monitoring the electrode array integrity and the patient's response to stimuli from the implant. In a comparison between NR, impedance and plain radiographs in 277 patients with normal cochlear anatomy, [PERSON] et al. [15] showed that radiographs were superior to NR and impedance and concluded that only radiographs may be used independently in the decision to remove a misplaced array intraoperatively. In a study by [PERSON] et al. [18], six patients with tip fold-overs demonstrated by imaging were reviewed. Impedance and NR were normal in all six, demonstrating their low predictive value for misplacement. In  
Figure 5: Case 4, tip fold-over. (**A**)—Original, (**B**)—Electrodes are highlighted for demonstration. this report, other electrophysiological tests (electrical field imaging and SOE) were abnormal. However, those tests were conducted postoperatively; therefore, the implants were not replaced and the deactivation of some electrodes was needed. [PERSON] et al. [11] compared intraoperative SOE testing to imaging (3-D rotational X-ray) in 72 ears for the diagnosis of tip fold-over.