|Year : 2022 | Volume
| Issue : 2 | Page : 135-138
Preoperative and intraoperative evaluation of round window configuration during cochlear implant in children
Jyoti Singh1, Jayant Prakash2, Sarita Kumari Mishra1, Shruti Jha1, Rakesh Kumar Singh1
1 Department of ENT, Indira Gandhi Institute of Medical Sciences, Patna, Bihar, India
2 Department of Paediatrics, Indira Gandhi Institute of Medical Sciences, Patna, Bihar, India
|Date of Submission||03-Feb-2022|
|Date of Acceptance||24-Mar-2022|
|Date of Web Publication||21-Sep-2022|
Dr. Rakesh Kumar Singh
Department of ENT, Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna - 800 014, Bihar
Source of Support: None, Conflict of Interest: None
Context: To establish a reliable factor for predicting the anticipated difficulty and adequacy of niche drilling without damaging the intracochlear structures during cochlear implant (CI) surgery. Aims: This study aimed to access the correlation of the distance from round window-to-vertical facial canal and round window to pyramid with the visibility of round window intraoperatively. Settings and Design: A prospective observational study of CI surgeries was conducted in the E.N.T. Department of Indira Gandhi Institute of Medical Sciences, Patna, from December 2019 to December 2021. The study included 30 children aged <5 years who presented to the E.N.T. OPD with prelingual deafness and were diagnosed with bilateral severe-to-profound hearing loss. Subjects and Methods: The preoperative high-resolution computed tomography images in the axial cut bone window setting at round window level were used to calculate the distance of round window-to-vertical facial canal and round window to pyramid on the RadiAnt DICOM Viewer. The intraoperative visibility was assessed through the recordings of the operation. Statistical Analysis Used: The data were analyzed using the MS Office 2019 Excel spreadsheet (Microsoft Corp., Redmond, WA, USA) and the program IBM SPSS 28.0.0 (SPSS Inc., Chicago, IL, USA). One-way analysis of variance was used. Results: A significant difference existed between round window and vertical facial canal distance measured preoperatively with the three categories of visibility of round window intraoperatively (P = 0.033), but a weak significant difference was found with the distance of round window to the pyramid with the visibility of round window (P > 0.05). Conclusions: Preoperative computed tomography measurement of the round window and vertical facial canal is a reliable predictor of a round window configuration that may aid in predicting the round window visibility.
Keywords: Distance, pyramidal eminence, round window, vertical facial canal
|How to cite this article:|
Singh J, Prakash J, Mishra SK, Jha S, Singh RK. Preoperative and intraoperative evaluation of round window configuration during cochlear implant in children. Indian J Otol 2022;28:135-8
|How to cite this URL:|
Singh J, Prakash J, Mishra SK, Jha S, Singh RK. Preoperative and intraoperative evaluation of round window configuration during cochlear implant in children. Indian J Otol [serial online] 2022 [cited 2022 Sep 25];28:135-8. Available from: https://www.indianjotol.org/text.asp?2022/28/2/135/356449
| Introduction|| |
Cochlear implants (CIs) are a well-accepted treatment for patients with severe-to-profound sensorineural hearing loss who have failed to respond to conventional hearing augmentation. In conjunction with time, tremendous refinements took place in device development and surgical techniques. One of these sophistications was to adopt round window insertion over cochleostomy. Hence, more emphasis is being placed to understand the detailed configuration of the round window and its surrounding structures. The round window membrane (RWM) is normally hidden beneath a bony overhang called the round window niche (RWN), which is formed by a posterior pillar, tegmen, and an anterior pillar., RWM with its niche is referred to as a round window prechamber. Prior knowledge of the topographic anatomy of a round window,, its visibility, the direction of opening, and distances from various adjacent structures in the tympanum, are required for successful CI surgery. This knowledge can aid in decision-making before surgery and is very useful in avoiding complications such as misplacement into extracochlear sites, traumatic injury to intracochlear structures, and iatrogenic injury to surrounding structures.
The importance of imaging in the preoperative evaluation of CI recipients cannot be overstated. If the degree of associated difficulties were known before surgery, the success rate of the surgery would be high. Vaid et al. and Chemburkar formulated 10-point and 12-point scoring systems respectively based on imaging findings and calculated potential difficulty scores., The anatomical variations in the round window can also influence the feasibility of RWM exposure through posterior tympanotomy, and a high-resolution computed tomography scan (HRCT scan) can be used to predict the difficulty of RWM exposure. The study is being done to find if preoperative simple parameters can be used to predict the round window configuration which can help in surgical planning which will be more beneficial for less experienced surgeons in decision-making.
| Subjects and Methods|| |
A prospective observational study of CI surgeries was conducted at the E.N.T. Department of Indira Gandhi Institute of Medical Sciences, Patna, from December 2019 to December 2021. The study included 30 children aged <5 years (18 boys and 12 girls) who presented to the E.N.T. OPD with prelingual deafness and were diagnosed with bilateral severe-to-profound hearing loss. Exclusion criteria were patients who had a cochlear malformation, an incomplete follow-up, explantation for any reason, postimplant major complications, device failure, or postimplant trauma. The study began after receiving approval from the institutional ethical committee with ethical clearance no 1196/IEC/IGIMS/2019.
Preoperative parameters for assessment
RadiAnt DICOM Viewer (64-bit) 2021.2 software was used to examine radiological images obtained from preoperative HRCT images of the temporal bone with a thickness of 0.5 mm in the bone window setting in an axial cut on the RWM plane displaying the basal turn of the cochlea with the RWM. The software's measurement tool was used to calculate the distance at this level of view. The distance was measured from the midpoint of the round window to the leading edge of the vertical section of the facial nerve and the pyramid.
Intraoperative parameters for assessment
All procedures were carried out by a single experienced surgeon who routinely performs CIs through the posterior tympanotomy round window approach. Following posterior tympanotomy, the RWN and membrane were identified. Recordings of the operation on a Karl Zeiss OPMI Vario S-8 microscope with a Sony recorder were used to carefully assess the visibility of the round window in every case. The visibility of the RWN during surgery is classified into three types based on the surgical view (i.e., through the posterior tympanotomy) as per the St. Thomas's Hospital classification of RWM.
- Type I = The exposure of 100% of the membrane
- Type II = subtotal exposure and is subclassified
- Type IIa = more than 50% but <100% of the membrane
- Type IIb = <50% but more than 0%
- Type III = The membrane can not be visualized at all even after the best surgical effort.
The data were analyzed using the MS Office 2019 Excel spreadsheet (Microsoft Corp., Redmond, WA, USA) and the program IBM SPSS 28.0.0 (SPSS Inc., Chicago, IL, USA). Using one-way analysis of variance (ANOVA), HRCT measurements between three different types of round window visibility were compared.
| Results|| |
Round window visibility was graded as Type I found in 5 (16.67%), Type IIa found in 14 (46.67%) patients, Type IIb found in 11 (36.67%) patients, and Type III was not found in any patients [Table 1] and [Table 2].
|Table 1: Comparative data of the visibility of round window with round window to vertical facial canal distance and round window to pyramid distance on high-resolution computed tomography of all patients|
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|Table 2: Tabulation of grading of visibility with mean round window to vertical facial canal distance and mean distance from the round window to the pyramid and their data analysis with a 5% level of significance|
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Comparison of round window visibility with preoperative HRCT distance from round window to vertical facial canal showed the mean distance between the round window and the vertical facial canal and the round window visibility for Type I, IIa, and IIb was 5.74 ± 1.3, 4.78 ± 1.3, and 4.15 ± 1.7, respectively [Table 2].
ANOVA test showed a significant difference between three categories of round window visibility and the distance from the round window to the vertical facial canal (P = 0.033) [Figure 1] and [Table 2].
|Figure 1: Histogram comparing average distance between round window to vertical facial canal on high-resolution computed tomography scan and round window for the three types of visibility. The mean distance decreases in Type IIb and Type IIa when compared to Type I|
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Comparison of round window visibility with preoperative HRCT distance from round window to pyramid showed the mean distance between round window to the pyramid and the round window visibility for Type Ia, IIa, and IIb was 5.06 ± 1.5, 4.75 ± 2.3, and 4.29 ± 0.7, respectively [Table 2]. ANOVA test showed a weak significant difference between three categories of round window visibility and distance from the round window to the pyramid (P = 0.052) [Figure 2] and [Table 2].
|Figure 2: Histogram comparing the average distance between round window to pyramid on high-resolution computed tomography scan and round window for the three types of visibility, but the relationship was nonsignificant|
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| Discussion|| |
CIs have transformed the management of patients with severe to profound hearing loss, allowing these patients to develop language and communicative skills comparable to peers of their age. To achieve the desired result, aggressive surgical planning is required to avoid any mishaps during surgery. Hence, before surgery, adopting the soft surgical principle in terms of electrode selection,,, suitable insertion trajectory, and acquaintance with surgical difficulties like the distance of round window to the surrounding neurovascular structures, will allow gaining the maximum anticipated benefit.
In this study, parameters related to topographic round window configuration were investigated to determine whether any parameter would aid in preoperative decision-making and whether any parameter could predict the visibility of the round window. A more reliable and simple distance has been calculated on preoperative HRCT to represent the round window configuration that is the distance from round window to vertical facial canal and round window to the pyramidal eminence which can help to determine whether the round window is favorable or unfavorable for insertion. This distance has the advantage of being easily estimated in the preoperative HRCT, as HRCT radiographic assessment is being done in all cases while preparing for cochlear implantation. A significant difference between the three categories of round window visibility and the distance from the round window to the vertical facial canal was found (P = 0.033). If this distance is less, RW visibility will be poor which means that more drilling into the facial recess as well as RWN will be required for an adequate visualization along with modifications intraoperatively like adjustment of microscope or positioning of head more toward the surgeon to visualize posteriorly placed round window (Type IIa). While in our study round window to pyramidal eminence distance did not show any significant correlation with the round window visibility. Pendem et al., studied the round window to oval window distance and found that if this distance increases, visibility will be less while if the distance between incus short process and round window decreases, the visibility will be less.
Elzayat et al. studied the round window exposure and α angle (angle between the line from the leading edge of the facial nerve on the plane midpoint of RWM and median sagittal line) and found that the α angle was smaller for complete exposure and the unexposed round window has larger angle than partial exposure group.
| Conclusion|| |
As a result, HRCT measurements taken between reliable reproducible reference points in the middle ear can be used to predict round window visualization. The vertical facial canal, a definitive landmark, and the distance from the round window to the vertical facial canal can be used to identify and predict RWM visibility variations.
We thank Prof. (Dr.) N R Biswas, Director and Prof. (Dr) Manish Mandal, Medical Superintendent of the Institution for providing the hospital materials and administrative support to conduct this study. Our sincere appreciation to the patients and their relatives for their faith and support to us in this difficult pandemic period.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]