Cochlear Implant in cochlear Hypoplasia type 4 with Chiari Malformation- Case Report

Abstract

Cochlear hypoplasia type IV is a rare cochlear malformation with hypoplastic middle and apical turns while basal turn develops normally, it often coexist with other genetic mutations. We present a case of 4 year old with chiari malformation type 1 along with bilateral Cochlear hypoplasia type IV who underwent cochlear implantation.

Introduction

Inner ear malformations possess a great challenge for cochlear implantation, but in patients with existing cranial malformations, the complexity increases multiple folds. Cochlear hypoplasia is a subgroup of inner ear malformations (IEM) where external dimensions are less than those of a normal cochlea with other architectural deformity [1]. It is further classified in four subtypes [1]. Type IV cochlear hypoplasia (CH IV) is rarest and often found associated with genetic mutations [2, 3]. Chiari malformation is a congenital disorder due to defective closure of neural tube resulting in herniation of posterior fossa content below level of foramen magnum [4]. Any herniation or downward displacement of cerebellum is challenging situation for general anesthesia.

We are hereby reporting a case of cochlear implantation in a patient with cochlear hypoplasia type IV with existing Chiari malformation type 1 and the challenges faced during the surgery.

Case Report

A 4 year old female patient was born through C- section due to abnormally large and irregular head. At one year of age she was diagnosed with Chiari malformation type 1 by the pediatrician on basis of caudal displacement of the cerebellar tonsils through the foramen magnum in magnetic resonance imaging (MRI) findings (Fig. 1). She also had polydactyl. Patient had no developmental delay except speech and language milestones were not achieved till the age of 3.

Fig. 1.

MRI Brain (T1) mid sagittal image showing herniation of cerebellar tonsil in foramen magnum

She was referred to our centre where the hearing status was assessed by experienced audiologist using behaviour audiometry, pure tone audiometry, tympanometry and electrophysiological tests which included distortion product oto-acoustic emissions (DPOAE) testing and auditory brainstem response (ABR). The child was diagnosed with profound sensory neural hearing loss. There was no benefit from hearing aid. High resolution computed tomography (HRCT) of temporal bone demonstrated the cranial asymmetry with left hemisphere larger than right (Fig. 2). Mastoid cavity was contracted due to forward lying sigmoid sinus and low lying dural plate. Cochlea had hypoplastic middle and apical turn with normal basal turn (Fig. 3), which gives characteristic unwound appearance suggestive of cochlear hypoplasia type IV. MRI showed normal vestibulo-cochlear nerve. Neurosurgical intervention to be done when compression symptoms occur, for which 6 monthly MRI brain was suggested.

Fig. 2.

Left hemisphere larger than right

Fig. 3.

Cochlear hypoplasia type 4 (CH IV) with normal basal turn and hypoplastic middle and apical turns

Chiari malformation type 1 carries risk during of intubation due to neck extension causing pressure in cerebellum, hence fiber-optic guided intubation was done in this patient during general anesthesia. Left cochlear implantation was done by the trans-mastoid posterior tympanotomy facial recess approach. Due to difference in the spatial orientation between the facial recess and the cochlear basal turn, we had difficulty in identifying round window through posterior tympanotomy so the posterior canal wall was drilled and pushed anteriorly along with intact tympanomeatal flap for better visualisation of cochlea. MRI 3Tesla compatible cochlear implant CI622 was used; electrode insertion was done via round window. The posterior canal wall and tympanomeatal flap was repositioned. The radiographic findings confirmed that all of the electrodes were properly placed in the cochlea (Fig. 4). The cochlea opening was sealed with periosteal tissue. Intra operative neural response telemetry and impedance measurement were done.

Fig. 4.

Post operative HRCT temporal bone axial view with implant left in situ

Discussion

Cochlear hypoplasia is a development arrest in organogenesis during sixth week of gestational age. In CH IV the cochlea has smaller external dimensions with normal basal turn and hypoplastic middle-apical turn [1]. Robson described the cochlea as characteristic “unwound” appearance by anterior offset of hypoplastic middle and apical turn away from a tapered basal turn in patient of brachio-oto-renal syndrome as most frequent petrous bone finding [5]. Walker- Warburg syndrome patient also reported similar feature of cochlea [3]. Sennaroglu et al. reported a case of CH IV with significant family history of Cochlear implant in mother [1] .These studies signify the prominent genetic involvement of CH IV. In our case there was significant history of consanguinity found in the family. Patient also had multiple congenital malformations but no parent or sibling reported any cochlear malformation or hearing loss.

The hearing loss in CH IV is also quite variable. Cinar et al. found that among all patients with CH IV 46.2% of patient had severe to profound hearing loss, 46.2% patient only had moderate to moderately severe hearing loss and one patient (7.7%) had slight to mild hearing loss[6]. Sennaroglu et al. also reported 22 year old patient with bilateral moderate hearing loss but patient’s mother had same malformation with profound hearing loss and is cochlear implant recipient[1]. Our patient reported severe to profound hearing loss. Hence more studies are required to understand the pattern of hearing loss in CH IV.

Amaral et al. reported cochlear implantation in Chiari malformation type 2 with profound sensory neural hearing loss, along with 6 year follow-up performing well speech and hearing [7]. Despite the patient’s neurological conditions, the same does not lead or interfere with the auditory performance after cochlear implant [7]. As serial MRI are required in Chiari malformation to assess disease progression and future surgical intervention, it is advisable to use MRI (3 Tesla) compatible cochlear implant.

The lack of rostral development of the cochlea may lead to abnormal spatial orientation of cochlea.[1] Our case had altered angulation of cochlea resulting need of elevation of canal wall anteriorly along with tympanomeatal flap order to find the round window for implant insertion in scala tympani. Advancing technologies and improvement in quality of cochlear implant and better training of cochlear implant team has widen the candidacy for this type of rehabilitation. Due to the anomalous and reduced neural tissue distribution in cochlear hypoplasia, outcome remains uncertain [6].

Conclusion

Radio imaging has been vital for the correct diagnosis and adequate preoperative evaluation of cochlear implant candidates. Cranial and cochlear malformations can coexist and selection of MRI compatible implant is of utmost importance in cases of cranial malformations, requiring MRI brain in future.

Funding

This study was not funded by any source.

Declarations

Ethical Approval

All procedures performed in studies involving human participants were in.