Can Preoperative High Resolution Computed Tomography Be Rationalized in Adult Cochlear Implant Candidates?

Preoperative Imaging in Cochlear Implants

OBJECTIVE

To determine the utility of computed tomography (CT) and magnetic resonance imaging (MRI) in cochlear implant candidates.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral hospital.

PATIENTS

A total of 207 cochlear implanted patients with CT and/or MRI.

INTERVENTIONS

N/A.

MAIN OUTCOME MEASURES

Age versus abnormal radiologic findings, imaging abnormality versus postoperative outcomes, postoperative outcomes versus electrode design, Cambridge Cochlear Implant Protocol (CCIP) status for imaging abnormalities, sensitivity and specificity of CT and MRI for round-window/cochlear occlusion, and MRI for incomplete partitions.

RESULTS

A total of 207 patients with CT, MRI, or both were reviewed retrospectively. Less than half (15.5%) of CT scans had findings that might affect surgical intervention compared with 5.9% of MRI. No significant difference was found between children and adults for relevant imaging abnormalities (grade 4 or higher) with either CT (p = 0.931) or MRI (p = 0.606). CCIP status correlated with cochlear abnormalities (p = 0.040); however, only 46.2% of radiographic abnormalities on CT would be identified by these criteria. For detecting cochlear occlusion requiring surgical intervention, the sensitivity and specificity for CT were 40% (4 of 10; 95% confidence interval [CI], 12.16-73.76) and 95.73% (95% CI, 91.40-98.27), respectively. For MRI, the sensitivity and specificity were 33.33% (1 of 3; 95% CI, 0.84-90.57) and 96.97% (63 of 65; 95% CI, 89.32-99.63), respectively. There was no difference for postoperative AzBio scores for higher-grade imaging abnormalities (p = 0.6012) or for electrode designs (p = 0.3699).

CONCLUSIONS

Significant radiographic abnormalities were relatively uncommon in cochlear implant patients on either CT or MRI at our single-center institution. If present, abnormal imaging findings rarely translated to management changes. CCIP status does not reliably predict which patients are likely to have abnormalities. Both MRI and CT have low sensitivity for round-window or cochlear occlusion, but detection likely leads to changes in surgical management.

CT imaging-based approaches to cochlear duct length estimation-a human temporal bone study

Objectives

Knowledge about cochlear duct length (CDL) may assist electrode choice in cochlear implantation (CI). However, no gold standard for clinical applicable estimation of CDL exists. The aim of this study is (1) to determine the most reliable radiological imaging method and imaging processing software for measuring CDL from clinical routine imaging and (2) to accurately predict the insertion depth of the CI electrode.

Methods

Twenty human temporal bones were examined using different sectional imaging techniques (high-resolution computed tomography [HRCT] and cone beam computed tomography [CBCT]). CDL was measured using three methods: length estimation using (1) a dedicated preclinical 3D reconstruction software, (2) the established A-value method, and (3) a clinically approved otosurgical planning software. Temporal bones were implanted with a 31.5-mm CI electrode and measurements were compared to a reference based on the CI electrode insertion angle measured by radiographs in Stenvers projection (CDL_reference).

Results

A mean cochlear coverage of 74% (SD 7.4%) was found. The CDL_reference showed significant differences to each other method (p < 0.001). The strongest correlation to the CDL_reference was found for the otosurgical planning software-based method obtained from HRCT (CDL_SW-HRCT; r = 0.87, p < 0.001) and from CBCT (CDL_SW-CBCT; r = 0.76, p < 0.001). Overall, CDL was underestimated by each applied method. The inter-rater reliability was fair for the CDL estimation based on 3D reconstruction from CBCT (CDL_3D-CBCT; intra-class correlation coefficient [ICC] = 0.43), good for CDL estimation based on 3D reconstruction from HRCT (CDL_3D-HRCT; ICC = 0.71), poor for CDL estimation based on the A-value method from HRCT (CDL_A-HRCT; ICC = 0.29), and excellent for CDL estimation based on the A-value method from CBCT (CDL_A-CBCT; ICC = 0.87) as well as for the CDL_SW-HRCT (ICC = 0.94), CDL_SW-CBCT (ICC = 0.94) and CDL_reference (ICC = 0.87).

Conclusions

All approaches would have led to an electrode choice of rather too short electrodes. Concerning treatment decisions based on CDL measurements, the otosurgical planning software-based method has to be recommended. The best inter-rater reliability was found for CDL_A-CBCT, for CDL_SW-HRCT, for CDL_SW-CBCT, and for CDL_reference.

Key Points

• Clinically applicable calculations using high-resolution CT and cone beam CT underestimate the cochlear size.

• Ten percent of cochlear duct length need to be added to current calculations in order to predict the postoperative CI electrode position.

• The clinically approved otosurgical planning software-based method software is the most suitable to estimate the cochlear duct length and shows an excellent inter-rater reliability.

Adult Onset Bilateral Cochlear Nerve Atrophy and Cochlear Implantation: A Case Report and Review of the Literature

OBJECTIVE

To describe a case of idiopathic bilateral cochlear nerve atrophy acquired in adulthood.

PATIENT

A 75-year-old male with acquired bilateral cochlear nerve atrophy.

INTERVENTION(S)

Unilateral cochlear implantation.

MAIN OUTCOME AND RESULTS

Description of a patient with acquired bilateral cochlear nerve atrophy diagnosed at the age of 75. The patient had normal hearing and no communication deficits until the age of 66. At this point, the patient demonstrated a slight asymmetric hearing loss, which progressed to severe sensorineural hearing loss. Due to the resulting communication deficit, cochlear device implantation candidacy was pursued. Pre-operative magnetic resonance imaging (MRI) showed severe atrophy versus absence of the cochlear nerves bilaterally. After careful counseling regarding the expected communication outcomes given the MRI findings, the patient underwent left-sided cochlear implantation. The patient gained sound awareness, but no additional communication benefit compared to pre-operative baseline abilities.

CONCLUSION

Cochlear nerve deficiency is a known finding in certain cases of congenital and acquired hearing loss, but no cases of idiopathic adult-onset bilateral nerve atrophy have been reported. Without MR imaging, the clinically significant finding would not have been identified. Thus, MRI is advantageous when compared with other imaging modalities in patients with progressive sensorineural hearing loss and enables improved patient counseling regarding expected auditory and communication outcomes.