Elevated modiolus density on high-resolution computed tomography as an indicator of cochlear neurodysplasia: a retrospective case-control study
Kun Zhu1,2,3,4, Xin Chen1,2,3,4
Contributions: (I) Conception and design: Both authors; (II) Administrative support: X Chen; (III) Provision of study materials or patients: Both authors; (IV) Collection and assembly of data: K Zhu; (V) Data analysis and interpretation: X Chen; (VI) Manuscript writing: Both authors; (VII) Final approval of manuscript: Both authors.
Background: Cochlear neurodysplasia (CND) is recognized as a contributing factor to sensorineural hearing loss in children. This study aimed to investigate the relationship between modiolus density on high-resolution computed tomography (HRCT) and CND, and to evaluate its performance in diagnosing CND.
Methods: This retrospective study collected HRCT images of 34 patients diagnosed with unilateral neurological hearing loss in the Children’s Hospital of Chongqing Medical University from March 2018 to December 2023, who were also diagnosed with unilateral CND by computed tomography (CT) and magnetic resonance imaging (MRI) hydroimaging. CT values of the modiolus and petrous bone were measured on the affected and healthy sides, in addition to determining the width of cochlear nerve foramina and the width of internal auditory tract. The receiver operator characteristic (ROC) curve was used to evaluate the diagnostic performance of these features. Simultaneously, comparisons were conducted with parameters obtained from normal children. A total of 29 patients without CND were randomly selected as a control group.
Results: The unilateral sensorineural hearing loss group had 34 patients, comprising 18 males and 16 females, with a median age of 4.5 years, ranging from 0.7 to 11 years. The normal children group consisted of 20 males and 9 females, with a median age of 5.9 years, ranging from 0.5 to 12.0 years. Statistically significant differences were observed in the CT values of the modiolus, modiolus/petrous bone CT value ratio, width of cochlear nerve foramina, and width of internal auditory tract between the affected and healthy sides in patients with unilateral sensorineural hearing loss (P<0.05). The area under the ROC curve (AUC) of the modiolus CT value and the width of cochlear nerve foramina for the diagnosis of unilateral sensorineural hearing loss was 0.98 [95% confidence interval (CI): 0.95–1.00] and 0.99 (95% CI: 0.98–1.00), respectively. the modiolus density was significantly elevated in the affected sides in patients with unilateral CND. The optimal cut-off value of modiolus CT values was 983 Hounsfield unit (HU).
Conclusions: The elevated density of the modiolus on HRCT holds significant value in diagnosing CND.
Keywords: Children; cochlear neurodysplasia (CND); high-resolution computed tomography (HRCT); unilateral sensorineural hearing loss; elevated modiolus density
Submitted Feb 22, 2024. Accepted for publication Jul 10, 2024. Published online Jul 25, 2024.
doi: 10.21037/qims-24-308
Introduction
Cochlear neurodysplasia (CND) is recognized as a contributing factor to sensorineural hearing loss in children (1). CND affects approximately 0.8–1.8% of children with profound deafness (2). Research has demonstrated that there may be an association between CND and maternal diabetes and neonatal intensive care unit (NICU) admission (3). Magnetic resonance imaging (MRI) is commonly used to observe the status of the facial nerve and the vestibulocochlear nerve. However, MRI may not show the facial and vestibulocochlear nerves inside due to a lack of contrast when the inner ear canal is narrow (4,5), and due to resolution limitations, underdevelopment of the cochlear nerve may appear as an absence of the cochlear nerve in MRI. High-resolution computed tomography (HRCT) of the temporal bone is frequently employed to assess the conditions of the internal auditory canal and the bony labyrinth. Recent research has consistently shown that measurement of the width of the bony canal for the cochlear nerve in HRCT images is associated with the development of the cochlear nerve (6-8). Therefore, HRCT combined with MRI is often used in the diagnosis of CND (9,10). In this study, we quantitatively investigated the diagnostic value of increased modiolus density in identifying CND. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-24-308/rc).
Methods
Patients
This is a retrospective case-control study. We included 34 patients diagnosed with CND at the Children’s Hospital of Chongqing Medical University between March 2018 and December 2023, who were also diagnosed with unilateral CND by computed tomography (CT) and MRI water imaging. To be eligible for inclusion in this study, patients had to meet the following inclusion criteria: (I) aged <16 years; (II) oblique sagittal water imaging of the vertical internal auditory canal shows that the low signal of the cochlear nerve in the lower quadrant before the basal level image of the internal auditory canal is significantly thin or not displayed; (III) no auditory brainstem response; (IV) unilateral CND. The exclusion criteria were as follows: bilateral cochlear nerve dysplasia; other cochlear malformations; infections; tumors (Figure 1).
This retrospective study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Institutional Review Board of Children’s Hospital of Chongqing Medical University (Issue No.194[2024]) and the requirement for informed consent for this retrospective analysis was waived. The study also collected normal HRCT images of the auriculotemporal area. A total of 29 patients without CND were randomly selected as a control group. Control group cases underwent ear and temporal HRCT scans and were excluded from the study if they met any of the following exclusion criteria: hearing loss, cochlear deformities, infections, and tumors.
HRCT imaging protocol
HRCT scans were performed using a Philips Brilliance iCT scanner (Philips Healthcare, Amsterdam, Netherlands). Patients were positioned supine for scanning from the superior temporal bone to the tip of the papilla. Scanning parameters were as follows: layer thickness of 0.625 mm, pitch of 0.25, duration of 7–8 seconds, tube voltage of 120 Kv, and tube current of 125 mA. The layer spacing was set at 0.2 mm, with a matrix size of 1,024×1,024. Thin layer reconstruction was conducted using a bone algorithm. For image analysis, the Philips IntelliSpace Portal workstation was utilized, employing axial observation and multi-plane recombination as needed. The horizontal semicircular canal plane was selected as the standard reference plane.
Measurement method
In axial HRCT images, the central plane of the modiolus was selected with the baseline aligned parallel to the horizontal semicircular canal plane. The area of interest (AOI) for the modiolus, ranging from 20 to 30 pixels, was outlined, as well as the AOI for the medial petrosal part of the cochlea at the same level for the measurement of averaged CT values. The width of the internal auditory canal was determined by measuring the distance between its widest level and the mid-point, perpendicular to the longitudinal axis. The width of the cochlear nerve foramina was defined as the maximum inner diameter at the juncture between the base of the internal auditory canal and the modiolus. Measurements were performed 3 times by 2 experienced radiologists with over 10 years of practice, and the average of these measurements was recorded. Examples of these measurements are shown in Figures 2,3.
Statistical analysis
The software SPSS 23.0 (IBM Corp., Armonk, NY, USA) and RStudio (version 4.2.2; R Foundation for Statistical Computing, Vienna, Austria) were used for statistical analysis. To compare the quantitative parameters derived from HRCT between the affected and healthy sides in patients with unilateral sensorineural hearing loss, parameters conforming to a normal distribution were analyzed using the Shapiro-Wilk test and represented by mean and standard deviation, and a paired samples t-test was used to compare the quantitative parameters between the affected and healthy sides. When comparing the quantitative parameters derived from HRCT between patients with unilateral sensorineural hearing loss and normal children, an independent samples t-test was used to compare the quantitative parameters between groups. The receiver operator characteristic (ROC) curve was used to evaluate the diagnostic performance of these quantitative parameters, and the area under the ROC curve (AUC) and the corresponding 95% confidence interval (CI) were calculated. The Delong test was used to compare the diagnostic performance of these quantitative parameters. To internally validate the diagnostic performance of these quantitative parameters, the bootstrap resampling method was performed with 1,000 bootstrap resamples. A P value was less than 0.05 (2-sided) indicated a statistically significant difference.
Results
Demographic data
The unilateral sensorineural hearing loss group had 34 patients, comprising 18 males and 16 females, with a median age of 4.5 years, ranging from 0.7 to 11 years, and the mean age was 4.04±3.25 years. Among them, 20 patients had left-sided unilateral sensorineural hearing loss, and 14 had right-sided unilateral sensorineural hearing loss. The normal children group consisted of 20 males and 9 females, with a median age of 5.9 years, ranging from 0.5 to 12.0 years (mean age, 5.19±2.77 years) (Table 1).
Table 1
| Demographic | CND group | Control group | P value |
|---|---|---|---|
| Age (years) | 4.04±3.25 | 5.19±2.77 | 0.14 |
| Sex | 0.20 | ||
| Male | 18 | 20 | |
| Female | 16 | 9 |
Data are presented as number or mean ± standard deviation. CND, cochlear neurodysplasia.
Table 2 presents the comparison of HRCT quantitative parameters between the affected and healthy sides in patients with unilateral sensorineural hearing loss. Significant differences were found in the modiolus CT values, modiolus/petrous bone CT value ratio, cochlear nerve foramina width, and internal auditory canal width between the affected and healthy sides (P<0.05). However, no significant differences were observed in the petrosal bone CT values between the affected and healthy sides (P>0.05).
Table 2
| Quantitative parameters | Left sensorineural hearing loss (n=20) | Right sensorineural hearing loss (n=14) | |||||
|---|---|---|---|---|---|---|---|
| Affected side | Healthy side | P value | Affected side | Healthy side | P value | ||
| CT values of modiolus (HU) | 1,351.45±173.77 | 784.85±93.71 | <0.001 | 1,307.14±234.71 | 771.14±152.09 | <0.001 | |
| CT values of petrous bone (HU) | 1,953.10±84.96 | 1,939.65±81.13 | 0.293 | 1,954.64±60.16 | 1,941.86±91.50 | 0.307 | |
| Modiolus/petrous bone CT value ratio | 0.69±0.10 | 0.40±0.05 | <0.001 | 0.67±0.11 | 0.40±0.08 | <0.001 | |
| Width of cochlear nerve foramina (mm) | 0.99±0.50 | 2.31±0.24 | <0.001 | 0.69±0.59 | 2.34±0.26 | <0.001 | |
| Width of internal auditory tract (mm) | 4.01±0.82 | 4.64±0.71 | 0.002 | 3.44±0.85 | 4.50±0.61 | 0.002 | |
Data are presented as mean ± standard deviation. HRCT, high-resolution computed tomography; CT, computed tomography; HU, Hounsfield units.
Diagnostic performance of modiolus CT value and cochlear nerve foramina width
The AUC for diagnosing unilateral sensorineural hearing loss based on the CT values of the modiolus was 0.98 (95% CI: 0.95–1.00). The mean AUC of the 1,000 bootstrap resamples was 0.984 (95% CI: 0.983–0.985) (Figure 4A). The optimal cut-off value of modiolus CT values was 983 Hounsfield units (HU), and the sensitivity and specificity were 0.971 and 1.000, respectively. Similarly, the AUC value for diagnosing unilateral sensorineural hearing loss based on the width of the cochlear nerve foramina was 0.99 (95% CI: 0.98–1.00). The mean AUC of the 1,000 bootstrap resamples was 0.989 (95% CI: 0.988–0.990) (Figure 4B). DeLong test showed there was no significant difference between the CT values of the modiolus and the width of the cochlear nerve foramina for diagnosing unilateral sensorineural hearing loss (P>0.05). These results indicate the diagnostic value of the modiolus CT value and the width of the cochlear nerve foramina.
Comparison of HRCT quantitative parameters between patients with unilateral cochlear nerve hearing loss and normal children
There were statistically significant differences in the modiolus CT values, modiolus/petrous bone CT value ratio, cochlear nerve foramina width, and internal auditory canal width between patients with unilateral cochlear nerve hearing loss and normal children (P<0.05), whereas the petrosal bone CT values demonstrated no statistically significant differences between patients with unilateral cochlear nerve hearing loss and normal children (P>0.05) (Table 3).
Table 3
| Quantitative parameters | Left side | Right side | |||||
|---|---|---|---|---|---|---|---|
| Patient group (n=20) | Normal group (n=29) | P value | Patient group (n=14) | Normal group (n=29) | P value | ||
| CT values of modiolus (HU) | 1,351.45±173.77 | 729.52±150.15 | <0.001 | 1,307.14±234.71 | 738.90±127.53 | <0.001 | |
| CT values of petrous bone (HU) | 1,953.10±84.96 | 1,918.59±73.80 | 0.137 | 1,954.64±60.16 | 1,933.21±100.36 | 0.467 | |
| Modiolus/petrous bone CT value ratio | 0.69±0.10 | 0.38±0.08 | <0.001 | 0.67±0.11 | 0.38±0.06 | <0.001 | |
| Width of cochlear nerve foramina (mm) | 0.99±0.50 | 2.29±0.43 | <0.001 | 0.69±0.59 | 2.25±0.38 | <0.001 | |
| Width of internal auditory tract (mm) | 4.01±0.82 | 4.77±0.64 | 0.001 | 3.44±0.85 | 4.97±0.82 | <0.001 | |
Data are presented as mean ± standard deviation. HRCT, high-resolution computed tomography; CT, computed tomography; HU, Hounsfield units.
Discussion
The cochlea is the foremost part of the labyrinth, located anterior and inferior to the vestibule. In the center of the cochlea, there is a conical modiolus, which a nerve bundles passes through (8). HRCT, with its high spatial and density resolution, distinctly portrays the modiolus as an irregular structure, whose density is lower than that of the petrous bone but higher than the membranous labyrinth in the mid-cochlea. For the HRCT diagnosis of cochlear nerve dysplasia, many studies have focused on the width of the bony cochlear nerve canal (BCNC). Dorismond et al. believed that BCNC stenosis (<1.4 mm) was a typical concomitant manifestation of CND (6). Komatsubara et al. showed that the width of the cochlear nerve foramina was less than 1.5 mm was the diagnostic basis of CND (8). In this study, the AUC value of for diagnosing unilateral sensorineural hearing loss based on the width of the cochlear nerve foramina was 0.99 (95% CI: 0.98–1.00). However, our study demonstrated 4 cases with CND in which the cochlear nerve canal appeared normal on CT. These cases join several examples described by Chin et al. and Casselman et al. (5,10). Concurrently, this study emphasized the density of the modiolus, which revealed the relationship between modiolus density on HRCT and CND. The AUC of the modiolus CT value for the diagnosis of unilateral sensorineural hearing loss was 0.98 (CI: 0.95–1.00), indicating high diagnostic accuracy. There were significant differences in the ratio of CT values between the modiolus and petrous bone on the affected and normal sides. This may be due to the reduction in components of the nerve tract and spiral ganglion in cases of CND, leading to a decrease in ossification inhibition. This study showed that the optimal cut-off value of modiolus CT values was 983 HU; CND should be suspected if the CT value exceeds this threshold. This study demonstrated that, in addition to the stenosis of the cochlear nerve foramina, an increased CT value of the modiolus can also indicate CND.
There are several limitations to this study that need to be considered. First, we need to acknowledge the limitations arising from the small sample size. Second, this is a retrospective study and selection bias is possible. Third, our research is single-centered and further verification from multi-center research is required.
Conclusions
The elevated density of the modiolus on HRCT holds significant value in diagnosing CND.
Acknowledgments
Funding: None.
Footnote
Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-24-308/rc
Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-308/coif). The authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This retrospective study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Institutional Review Board of Children’s Hospital of Chongqing Medical University (Issue No.194[2024]) and the requirement for patients’ informed consent for this retrospective analysis was waived.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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