Cochlear electrode array tip fold-over in incomplete partition-I - A case report

Estimation of outer-wall length in optimizing cochlear implantation in malformed inner ears

Estimation of cochlear length is gaining attention in the field of cochlear implants (CIs), mainly for selecting of CI electrode lengths. The currently available tools to estimate the cochlear duct length (CDL) are only valid for normal inner anatomy. However, inner ear malformation (IEM) types are associated with different degrees of cystic apices, limiting the application of CDL equations of normal anatomy inner ear. Therefore, this study aimed to understand the degree to which the outer wall (OW) is observed in different malformation types and to formulate mathematical equations to estimate the OW length (OWL) from cochlear parameters, namely the basal turn diameter (A-value) and width (B-value). Three-dimensional (3D) segmentation of promontory and fluid parts of the inner ear was performed to understand the extent to which the OW is visible to measure the OWL manually. Enlarged vestibular aqueduct syndrome (EVAS) was diagnosed in 37 ears, which consistently showed the extent of the OW to an angular depth of 540°, beyond which the cystic apex starts. Incomplete partition (IP) type I was observed in 30 ears, with the OW extending to only 360° of angular depth. IP type II was observed in 35 ears, with the OW extending to 450° of angular depth. IP type III was identified in 24 ears, with the OW observed for 540° of angular depth. Cavity-type malformations were observed in 36 ears, and circumference was measured in the axial view. A strong positive linear correlation was observed between the manually measured OWL and cochlear parameters for all malformation types analyzed. A multiple linear regression model was applied to formulate mathematical equations, which was further used to create a software application for estimating OWLs in IEM types, using cochlear parameters as inputs.

Incidence of Cochlear Implantation Complications in Saudi Arabia: A Comprehensive Systematic Review of the Literature

This review aimed to determine the incidence of complications associated with cochlear implants (CI) in Saudi Arabia. We systematically searched PubMed, AIRE, OaIster, MEDLINE, Directory of Open Access Journals, Scopus, and Ovid from inception to January 2024. The review protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (ID: CRD42023486687). Studies that reported CI complications in Saudi Arabia were included. This systematic review was conducted in accordance with PRISMA guidelines. A total of 17 articles with 2216 patients were included. The most common intraoperative complication was cerebrospinal fluid leakage (23 patients, 0.99%), followed by surgical difficulties (six patients, 0.26%), and dural accidental exposure and bleeding (three patients, 0.13%); the most common postoperative complications were vestibular symptoms (20 patients, 0.86%), followed by infection (17 patients, 0.73%), and device malfunction or migration (12 patients, 0.52%). The total complication rate ranged from 4-13%. Most of the included studies had a low risk. CI in Saudi Arabia has a complication rate similar to that reported in international studies. This review emphasizes the need for continued surveillance of CI outcomes to optimize procedural techniques and improve the safety and efficacy of CI in Saudi Arabia.

Method to estimate the basal turn length in inner ear malformation types

The mathematical equations to estimate cochlear duct length (CDL) using cochlear parameters such as basal turn diameter (A-value) and width (B-value) are currently applied for cochleae with two and a half turns of normal development. Most of the inner ear malformation (IEM) types have either  less than two and a half cochlear turns or have a cystic apex, making the current available CDL equations unsuitable for cochleae with abnormal anatomies. Therefore, this study aimed to estimate the basal turn length (BTL) from the cochlear parameters of different anatomical types, including normal anatomy; enlarged vestibular aqueduct; incomplete partition types I, II, and III; and cochlear hypoplasia. The lateral wall was manually tracked for 360° of the angular depth, along with the A and B values in the oblique coronal view for all anatomical types. A strong positive linear correlation was observed between BTL and the A- (r² = 0.74) and B-values (r² = 0.84). The multiple linear regression model to predict the BTL from the A-and B-values resulted in the following equation (estimated BTL = [A × 1.04] + [B × 1.89] - 0.92). The manually measured and estimated BTL differed by 1.12%. The proposed equation could be beneficial in adequately selecting an electrode that covers the basal turn in deformed cochleae.

A novel three-step process for the identification of inner ear malformation types

Objective

We hypothesize that visualizing inner-ear systematically in both cochlear view (oblique coronal plane) and in mid-modiolar section (axial plane) and following three sequential steps simplifies, identification of inner-ear malformation types.

Methods

Pre-operative computer-tomography (CT) scans of temporal bones of 112 ears with various inner ear malformation (IEM) types were taken for analysis. Images were analyzed using DICOM viewers, 3D slicer, and OTOPLAN®. The inner-ear was captured in the oblique-coronal plane for the measurement of length and width of cochlear basal turn which is also called as A-, and B-values respectively (Step 1). In the same plane, the angular-turns of lateral-wall (LW) of cochlear basal turn were measured (Step 2). As Step 3, the mid-modiolar section of inner ear was captured in the axial plane by following the A-value and perpendicular to cochlear view. From the mid-modiolar section, the outer-contour of inner ear was captured manually by following contrasting gray area between fluid filled and bony promontory and was compared to known resembling objects to identify IEM types (Step 3).

Results

Following reference values have emerged from our analysis: A-, and B-values (Step 1) on average are >8 mm and >5.5 mm respectively, in normal cochleae (NA), enlarged vestibular aqueduct syndrome (EVAS), incomplete partition (IP) type-I and -II, whereas it is <8 mm and <5.5 mm respectively, in IP type-III and cochlear hypoplasia (CH). Angular-turn of LW is consistently observed in cochlear basal turn (Step 2), is 540° in NA and EVAS, 450° in IP-II, and 360° in IP types I & III. In subjects with CH type, angular-turn of LW is either 360° or 450° or 540°. In true mid-modiolar section, outer-contour of inner-ear (Step-3), other than in CH and cystic inner-ear malformations, resembles recognizable shapes of known objects. Absence of EVA is an additional characteristic that confirms diagnosis of CH when the A-, B-values, and angular-turn of LW can be similar to other anatomical types. Drawing a straight line along posterior edge of internal auditory canal (IAC) in axial view can differentiate a true common cavity (CC) from cochlear aplasia-vestibular cavity (VC).

Conclusion

Three-step process proposed in this study captures inner-ear in cochlear view as well in mid-modiolar sections visualizing key features of inner-ear in identification of IEM types.

Level of Evidence

Level 1.

A novel cochlear measurement that predicts inner-ear malformation

The A-value used in cochlear duct length (CDL) estimation does not take malformed cochleae into consideration. The objective was to determine the A-value reported in the literature, to assess the accuracy of the A-value measurement and to evaluate a novel cochlear measurement in distinguishing malformed cochlea. High resolution Computer Tomography images in the oblique coronal plane/cochlear view of 74 human temporal bones were analyzed. The A-value and novel C-value measurement were evaluated as predictors of inner ear malformation type. The proximity of the facial nerve to the basal turn was evaluated subjectively. 26 publications report on the A-value; but they do not distinguish normal vs. malformed cochleae. The A-values of the normal cochleae compared to the cochleae with cochlear hypoplasia, incomplete partition (IP) type I, -type II, and -type III were significantly different. The A-value does not predict the C-value. The C-values of the normal cochleae compared to the cochleae with IP type I and IP type III were significantly different. The proximity of the facial nerve to the basal turn did not relate to the type of malformation. The A-value is different in normal vs. malformed cochleae. The novel C-value could be used to predict malformed anatomy, although it does not distinguish all malformation types.