Indian Journal of Otology

ORIGINAL ARTICLE
Year
: 2021  |  Volume : 27  |  Issue : 1  |  Page : 3--6

Inner ear malformations in cochlear implant recipients


Luan Viet Tran1, Vu Anh Duong2, Saim Lokman3,  
1 Department of Otolaryngology Head and Neck Surgery, Pham Ngoc Thach University of Medicine; Department of Otology, Ear Nose and Throat Hospital, Ho Chi Minh City, Vietnam
2 Department of Otology, Ear Nose and Throat Hospital, Ho Chi Minh City, Vietnam
3 School of Medicine, KPJ Healthcare University College, Nilai, Negeri Sembilan, Malaysia

Correspondence Address:
Assoc. Prof. Luan Viet Tran
Department of Otolaryngology Head and Neck Surgery, Pham Ngoc Thach University of Medicine, 02 Duong Quang Trung, District 10, Ho Chi Minh City
Vietnam

Abstract

Objective: The aim of this study is to determine the prevalence of the inner ear malformations (IEMs) in cochlear implant recipients according to Sennaroglu's classification, and to document the intraoperative difficulties and complications in those cases. Methods: This was a descriptive cross-sectional study performed at our hospital between January 2016 and October 2019. IEMs on temporal bone computed tomography scans were identified in all patients who received cochlear implants during the study. Intraoperative difficulties and complications relating to these malformations were described. Results: Twelve patients with IEMs were identified from a total of 212 cochlear implant recipients, representing a prevalence of 5.7%. Among them, one patient with incomplete partition (IP) Type I (8.3%), seven patients with IP Type II (58.3%), one patient with IP Type III (8.3%), one patient with cochlear hypoplasia (CH) Type I (8.3%), and two patients with CH Type III (16.7%) were identified. Associated enlarged vestibular aqueduct was found in four cases with IP Type II (33.3%). Round windows were not identified intraoperatively in 3 cases with CH (25%). Three cases (25%) had cerebrospinal fluid gusher (one patient in each of the following anomalies: IP-I, IP-II, and IP-III). The mean categories of auditory performance score was 6, which was collected within 23.3 months after the surgery. Conclusion: This study documents the prevalence of IEMs in cochlear implant recipients (classified by Sennaroglu in 2017). The identification of such anomalies will significantly aid surgeons in making decisions regarding cochlear implant candidacy and surgical strategy when cochlear implantation is contemplated to obtain optimal outcomes.



How to cite this article:
Tran LV, Duong VA, Lokman S. Inner ear malformations in cochlear implant recipients.Indian J Otol 2021;27:3-6


How to cite this URL:
Tran LV, Duong VA, Lokman S. Inner ear malformations in cochlear implant recipients. Indian J Otol [serial online] 2021 [cited 2021 Nov 27 ];27:3-6
Available from: https://www.indianjotol.org/text.asp?2021/27/1/3/329095


Full Text



 Introduction



Hearing loss is relatively common in children. The estimated prevalence of sensorineural hearing loss is 1.33 per 1000 live births.[1] Cochlear implant (CI) is proven to be the most beneficial in children with severe and profound hearing loss.

Computed tomography (CT) is performed in all CI candidates to evaluate important landmarks and assess any congenital or acquired anatomic abnormalities of the inner ear.[2],[3] Cochlear implantation has been performed in our country since 1998 with a growing number of CI recipients. We identified a number of inner ear malformations (IEMs) in cochlear implant recipients. The purpose of this study is to determine the prevalence of IEMs in cochlear implant recipients according to Sennaroglu's classification. How these IEMs affect the cochlear implantation was also discussed.

 Methods



Study design

This was a descriptive cross-sectional study performed at our hospital from January 2016 to October 2019. The protocol was approved by the ethics committee of our institution.

Imaging protocol and recruitment

Two hundred and twelve temporal bone CT scans of CI recipients were reviewed for IEMs according to Sennaroglu's classification. The CT scans was taken by a multi-detector, 64-slide CT scanner overlapping axial cuts of 0.5 mm thickness. The intermediate window and level settings were 4000 HU and 700 HU, respectively.

All scans were reviewed by two independent surgeons. If disagreements ensued, the scans were discussed and if a consensus was not achieved, a third surgeon would be involved. A consensus was achieved in all cases when this occurred.

All patients with IEMs were operated by the same experienced otoneurologists. Intraoperative difficulties and complications were documented in each case with IEMs.

All statistical analyses were performed with SPSS software version 22.0 (SPSS, IBM Corp. Armonk, NY, USA).

Classification

Sennaroglu's classification (2017) of the IEMs was used in this study. In this classification, IEMs are classified into eight distinct groups according to the differences observed in the cochlea.[4] They include the following: complete labyrinthine aplasia (known as Michel deformity), rudimentary otocyst, cochlear aplasia, common cavity, cochlear hypoplasia (CH), incomplete partition (IP), enlarged vestibular aqueduct (EVA), and cochlear aperture abnormalities. IP is subclassified into three types: IP-I, IP-II, and IP-III. CH is subclassified into subtypes CH-I, CH-II, CH-III, and CH-IV.

 Results



Twelve patients with IEMs were identified from a total of 212 patients who had cochlear implantation performed at our hospital from January 2016 to October 2019, representing a prevalence of 5.7%. The average age of patients was 5.67 years (range 2–13, standard deviation 3.82). The male to female ratio was 1.4:1.

Among these 12 patients, the most common IEMs were IP type II (seven patients, 58.3%). There was one patient with IP Type I (8.3%), one patient with IP Type III (8.3%), one patient with CH Type I (8.3%), and two patients with CH Type III (16.7%). Associated EVA was found in four cases with IP Type II (33.3%). There was no patient with EVA alone [Table 1].{Table 1}

All 12 patients with IEMs underwent unilateral CI surgery. Implants with straight electrode arrays were used in 10 patients including 3 Medel and 7 Cochlear implants. Two other cases were implanted with Contour Advance CI24RE electrode. Round windows could not be identified intraoperatively in three cases with CH (25%). Cerebrospinal fluid (CSF) gusher occurred in three patients (25%) (one patient in each of the following anomalies: IP-I, IP-II, and IP-III) [Table 1]. All patients had Stenver's X-ray of the skull, 1 day after surgery, confirming the correct position of the electrode array.

The hearing and speech rehabilitation were assessed using categories of auditory performance (CAP) score collected within 23.3 months after implantation. There was one patient who was lost to follow-up after surgery. The mean CAP score was 6 (range 5–7, standard deviation 0.73).

 Discussion



Sennaroglu's classification of the IEMs has been used by many authors in medical literature. The first classification of IEMs was introduced by Jackler et al. in 1987 based on embryogenesis and development arrest.[5] It explains each malformation by the arrest of development at a different stage of embryogenesis: the arrest of development at different weeks produces different malformations. Afterward, Sennaroglu classified IP and CH into several subtypes based on CT scan for the first time in 2002.[5] Since then, he has modified the classification twice, in 2009 and 2017.[4],[6] The latest classification in 2017 was introduced with possible risks during surgery, as well as specific treatment options for these various abnormalities.[4]

In this study, the prevalence of IEMs was 5.7%. The prevalence of IEMs in the studies of Aldhafeeri and Alsanosi and Adibelli et al. was 7.5% and 9.8%, respectively.[7],[8] However, their studies also counted the semicircular canal and internal auditory canal (IAC) anomalies which were not listed in Sennaroglu's latest classification. Therefore, we recalculated cases of IEMs according to Sennaroglu's latest classification in their studies for comparison. Aldhafeeri and Alsanosi reported that IEMs were found in 16 patients among total of 316 patients reviewed, representing a prevalence of 5.1%.[8] Likewise, Adibelli et al. reported 37 patients with IEMs among 440 patients under the age of 18 years who had cochlear implantation, representing a prevalence of 8.4%.[7] We found no significant difference in the prevalence of IEMs in our study and their studies (P > 0.05).

IP-I is described as cochleovestibular malformation. In this group, the cochlea lacks the entire modiolus and interscalar septa (ISS), resembling an empty cystic structure. [Figure 1] Moreover, the facial nerve course is often anomalous. The distinction between IP-I and IP-II is particularly significant. IP-I is more severe than IP-II as IP-I has higher risk of CSF gusher (reported in 40%–50% of cases) because of the defect mentioned above. It has poorer results because of lacking residual neural activity. Another important issue is the associated EVA, which contributes to the high risk of CSF gusher, although this anomaly rarely happens.[9] There was one patient with IP-I in our study who had CSF gusher during the surgery and the straight electrode array was used in this patient.{Figure 1}

IP-II was the most common abnormality in our study (58.3%). Chadha et al. and Kim et al. noted that IP-II was also the most common IEMs in their studies.[10],[11] In IP-II, the apical part of the modiolus is defective. [Figure 2] This abnormality was originally described by Carlo Mondini, together with dilated vestibule and EVA constitute the triad of the Mondini deformity. In IP-II, since the cochlea has normal dimensions, facial nerve abnormality is very rare. Therefore, the standard approach can be used in all patients with IP-II and all kinds of electrodes can be used because of normal basal part of the modiolus.[12] However, the CSF gusher was sometimes observed during surgery, especially with associated EVA. This is mainly because of modiolar defects occurring as a result of high CSF pressure transmission into the inner ear.[13] In fact, all types of electrodes were implanted in seven of our patients (6 straight and 1 precurved electrode arrays) in which there was only one patient had CSF gusher.{Figure 2}

In IP-III, the ISS are present, but the modiolus is completely absent. [Figure 3] Two serious drawbacks may occur during CI surgery: gusher always occurring due to the large defect between the cochlea and the IAC, and electrode misplacement into the IAC because of the defective modiolus. Therefore, straight electrodes that provide one full turn around the cochlea are preferable and the position of the electrode should be checked by an intraoperative X-ray. If the electrode is discovered to be in the IAC, it should be repositioned during surgery.[12] In our study, the patient with IP-III (Patient No. 4) had CSF gusher during cochleostomy and was implanted with straight electrode.{Figure 3}

When gusher occurred, the cochleostomy was drilled larger while the head of the operating table was elevated to reduce the intracranial CSF pressure. Suction was applied at the edge of the cochleostomy to guide the CSF out of the cochleostomy while inserting the electrode into it. Pieces of muscle or fascia were packed tightly into the cochleostomy around the electrode. We waited 10–15 min until no CSF leak noted.

The round window was not identified through the facial recess in three cases of CH. This can be explained by the anomaly of promontory protuberant because of hypoplastic cochlea, [Figure 4] leading to the difficulty in identifying the round window niche. Furthermore, the thinner and shorter electrodes should be used to obtain full insertion.[12] Two patients in our series had straight electrodes for this reason. Zhu et al. measured the average distance between the oval window and the round window niche as 3.74 mm.[14] In our practice, we identified the round window niche about 4 mm below the oval window, and the cochleostomy was performed at this area to find out scala tympani lumen for inserting the electrode array.{Figure 4}

The vestibular aqueduct is a small canal within the temporal bone, running from the vestibule to the posterior fossa and containing the endolymphatic duct and endolymphatic sac. During embryogenesis, the vestibular aqueduct starts as a long and narrow vestibular diverticulum. When the problem occurs before this diverticulum starts to narrow, it keeps its embryonic large dimensions, results in an EVA.[15] EVA may cause high CSF pressure transmission into the inner ear which leads to a high risk of CSF gusher that affects surgical management, especially the electrode insertion.

The result of postoperative skull X-ray revealed a good position and no kinking of the electrode array in 12 patients. CAP scores have been used in the assessment of the efficacy of speech rehabilitation after cochlear implantation in our pediatric patients showing a good outcome after surgery. Most children could hear, understand, and be able to communicate reasonably.

 Conclusion



This study documents the prevalence of IEMs in cochlear implant recipients (classified by Sennaroglu in 2017) and the intraoperative difficulties in those cases. Understanding of such anomalies will significantly aid surgeons in making surgical decision to minimize intraoperative complications and to obtain optimal outcomes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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