Cochlear implants: Insertion assessment by computed tomography

Cochlear Duct Length Calculation: Comparison Between Using Otoplan and Curved Multiplanar Reconstruction in Nonmalformed Cochlea

OBJECTIVE

To describe a new method to measure the cochlear parameters using Otoplan software, and to compare it with the traditional method using curved multiplanar reconstruction (cMPR).

STUDY DESIGN

Retrospective analysis using internal consistency reliability and paired sample t test.

SETTING

Tertiary referral center.

PATIENTS

Thirty-four patients including 68 ears from a clinical trial were retrospectively reviewed.

MAIN OUTCOME MEASURES

The length, width, height (distances A, B, H), and cochlear duct length of each cochlea were measured independently using two modalities: Otoplan and cMPR. Internal consistency reliability of the two modalities was analyzed. The time spent on each measurement was also recorded.

RESULTS

Otoplan software was compatible with all radiological data in this series. Distances A, B, and H showed no significant differences between Otoplan (9.33 ± 0.365, 6.61 ± 0.359, and 2.91 ± 0.312 mm) and cMPR (9.32 ± 0.314, 6.59 ± 0.342, and 2.93 ± 0.250 mm). The average cochlear duct length calculated by Otoplan was 34.37 ± 1.481 mm, which was not significantly different from that calculated by cMPR (34.55 ± 1.903mm, p = 0.215). The measurements with Otoplan had better internal consistency reliability compared with those by cMPR, and measurements with a higher peak kilovoltage (140 kVp) CT scan showed further higher internal consistency reliability. Time spent on each cochlea by Otoplan was 5.9 ± 0.69 min, significantly shorter than that by cMPR (9.3 ± 0.72 min).

CONCLUSION

Otoplan provides more rapid and reliable measurement of the cochlea than cMPR. Furthermore, it can be easily used in the laptop computer.

Impact of Cochlear Implant Array Placement on Speech Perception

PURPOSE

To assess the role of flat panel computed tomography (FPCT) in the evaluation of cochlear implant (CI) electrode position and its relation to speech perception.

METHODS

From March 2015 to March 2019, we retrospectively enrolled deaf subjects ≥ 18 years who underwent unilateral CI by one surgeon, imaged with FPCT and assessed with disyllabic words score before CI and at 6 months of follow-up. We calculated the disyllabic score difference before CI and after CI (ΔSDS) and divided the subjects in favorable and unfavorable outcome groups using the median ΔSDS as a cutoff. We compared the demographic, clinical, electrode characteristics, and the CI positioning variables scalar position, surgical insertion depth (SID), linear insertion depth (LID), angular insertion depth (AID) and wrapping factor (WF).

RESULTS

We studied 50 subjects (F/M = 27/23; median age = 60.5 years, IQR: 50-70 years). The median ΔSDS was 80% (interquartile range [IQR]: 60-100%) in quiet and 80% (IQR: 47.5-100%) in noise. Of the subjects 23 demonstrated a favorable outcome and had earlier age at CI (median 52 years; IQR 45-67 years versus median 62 years; IQR: 56-71 years p = 0.032) and a significantly higher SID (median: 4.02 mm IQR: 3.00-5.35 mm versus median: 2.94 mm IQR: 2.06-3.90 mm; p = 0.029). No difference was found for LID (p = 0.977), AID (p = 0.302), and WF (p = 0.224). A logistic regression model built with the age at CI, number of CI electrodes, and the SID was significant χ2 ((df = 3, N = 50) = 14.517, p = 0.002). The model explained 33.7% (Nagelkerke R2) of ΔSDS variance and correctly classified 76% of the cases.

CONCLUSION

The SID measured by FPCT predicts the ΔSDS at 6 months follow-up, alongside with age at implantation and number of CI electrodes.

The discomallear ligament: anatomical, microscopical, and radiologic analysis

BACKGROUND

Several anatomic relationships between the ear and the temporo-mandibular joint have been proposed to account for the presence of tinnitus during temporo-mandibular disorders. Among the otomandibular structures, the discomallear ligament (DML) is interposed between the malleus and the retrodiscal capsular complex. The aim of present paper was to study through dissection the frequency and morphology of DML, to characterize its type of collagen, and to evaluate the DML on routine computed tomography (CT).

METHODS AND RESULTS

The study has been conducted on five un-embalmed adult cadavers, and in all cases, the DML was present (100%). It was constituted mainly by fibers of collagen I, with abundant elastic fibers. On CT exams of 40 patients with no reported pathology of the ear, on axial images, a dense structure, going from the upper end of the petrotympanic fissure to the neck of the malleus, was present in all the cases. In 90%, it showed a triangular shape, in 5% a rectangular shape, and in 5% a curved course. The mean length of the antero-medial side was 2 ± 0.6 mm and that of the antero-lateral side was 1.63 ± 0.5, and the mean area was 1.29 ± 0.83 mm².

CONCLUSION

The DML could represent an anatomical structure that joining the temporo-mandibular joint and the malleus may play a role in the otologic symptoms during temporo-mandibular disorders.