The role for cochlear implants in microtia and congenital aural atresia: A case report and a review of literature

Abstract

Sensorineural hearing loss resulting from microtia and aural atresia is rare due to different embryologic origins of the external and inner ear. Consequently, cochlear implants are seldom performed in patients with microtia and/or aural atresia. Herein we discuss an 8 year-old boy with congenital aural atresia and microtia who underwent cochlear implant surgery for profound hearing loss with good results. A literature review was performed and discussed. Pre-operative planning with high resolution computed tomography and facial nerve monitoring are crucial in identification and preservation of the facial nerve due to the high rate of aberrant anatomy. Careful incision placement is required particularly if pinna reconstruction is considered. Literature review highlighted various surgical approaches as well as different modalities used for intra-operative facial nerve monitoring. Only one patient had intra-operative complications. Cochlear implant is a viable solution in patients with external ear malformations and severe-profound sensorineural hearing loss. Adequate planning and counselling are essential due to the challenges that may occur in microtia and aural atresia.

Introduction

Patients with microtia or congenital aural atresia (AA) typically have conductive hearing loss due to absence of the ear canal and/or ossicular abnormalities. Sensorineural hearing loss (SNHL) in these patients is rare owing to the different embryological origins of the outer and inner ear. ¹ Hence, there is little information regarding cochlear implants (CI) in patients with congenital ear malformations and SNHL. Herein, we present a case of a child with microtia and AA who underwent a CI surgery.

Case report

An 8 year-old boy presented soon after birth because of failed Universal Newborn Hearing Screen (UNHS). He had no significant antenatal, perinatal or post-natal problems. He was born full-term. Examination revealed microcephaly (3rd percentile) and a right grade 3 lobular-type microtia with AA. The left pinna and ear canal were normal. His medical history included an atrial septal defect for which he underwent surgery at age 3. Auditory brainstem response (ABR) and Steady State Evoked Potential (SSEP) showed bilateral severe hearing loss (wave V seen at 70 dBHL on the left and at 70 dBHL for the right bone-conduction thresholds). He was fitted with a left-sided hearing aid (HA) at 8 months and commenced auditory-verbal therapy (AVT). His attendance was sporadic due to hospital phobia after his cardiac surgery. At age 6, he was referred for significant speech delay, scoring an age-equivalent of a 2 year-old on standardised assessments of language and speech. Although he used his left HA consistently, his speech was unclear and only his mother could understand him. He was able to answer only simple questions i.e. level 7 on the revised Categories of Auditory Perception (CAP) (The Shepherd Center, Nottingham CI programme 1995). A pure-tone audiometry (PTA) showed right profound hearing loss and left severe to profound SNHL. Left aided hearing thresholds were 35–45 dBHL. Aided speech discrimination was only 47%.

Because of the significant speech and language delay, the family was counselled for a right CI. Auricular reconstruction was also discussed. They were keen to explore this in future. The need to commit to intensive AVT was emphasized because of child’s age, significant speech and language delays and the prolonged auditory deprivation in the right ear.

High-resolution Computed tomography (HRCT) showed a 1.6 cm atretic plate (Figure 1). The fused malleoincudal complex was connected to the atretic plate via the rudimentary handle of malleus. The mastoid segment of the facial nerve was anteriorly displaced with a high-riding jugular bulb. The cochlear had normal configuration, although the cochlear nerve canal was slightly narrowed. Magnetic resonance imaging (MRI) showed bilateral cochlear nerve hypoplasia (left worse than right) (Figure 1).

Figure 1.

(Left) High resolution computed tomography (HRCT) of right temporal bone, axial image showing configuration of round window (RW), the malformed malleoincudal complex (MI) is partially imaged. (Right) Magnetic resonance imaging (MRI) axial cuts showing hypoplastic cochlear nerves.

Pre-operatively, the facial nerve monitor was set up. A template of the left ear was used to estimate the position of the reconstructed auricle (Figure 2). The incision was placed as far posteriorly as possible within the hair-bearing skin (2 cm posterior to the posterior limit of the template), to reduce compromise to the post-aural skin vasculature. A posteriorly based periosteal flap was created.

Figure 2.

(Left) A template was made of the contralateral ear and used to estimate the position of the reconstructed auricle. The incision was then positioned 2 cm posterior to the posterior limit of the template (indicated by the red arrows) (Right) Close-up view of placement of the incision.

The mastoid cortex and atretic plate were drilled, beginning along the temporal line postero-superior to the glenoid fossa and following the middle fossa plate down to epitympanum and to the ossicles. The facial nerve was identified and confirmed with a facial nerve monitor. The ossicles were exposed. The malformed malleo-incus complex was separated from the stapes and removed to allow better round window access. The posterior ledge was drilled down and the round window niche identified. As the facial nerve was displaced anteriorly, access to the round window membrane was difficult and a cochleostomy was performed anterior to the round window niche (Figure 3). An Advanced Bionics HiRes 90K Advantage with HiFocus MS Electrode was inserted easily through the cochleostomy with full insertion. Post-procedure, all neural response telemetry showed good waveforms. Electrode placement was confirmed on a modified Stenver’s view X-ray (Figure 4). The mastoid dressing was removed on post-operative day 1 and the patient was discharged home. No complications were encountered. 7 months post-surgery, his right-sided thresholds are 25–35 dBHL, he was able to identify Ling 6 sounds at a distance. There was a growth of vocabulary by 1 year and growth in grammatical morphemes by at least 6 months, using the Test for Auditory Comprehension of Language (TACL-4). With bimodal stimulation post-surgery, he was able to use the telephone with a familiar speaker (his mother) i.e. CAP improved from level 7 to level 11.

Figure 3.

(a) Intra-operative photo depicting malformed malleo-incudal complex (MI),articulating with stapes [S], arrow indicates incudostapedial joint. (b) MI complex removed, posterior ledge was then drilled down to expose round window niche. Arrow points to the round window niche. Dashed line indicates facial nerve (c) Cochleostomy (Co) performed. (d) Insertion of electrode into cochleostomy.

Figure 4.

Modified Stenver’s view X-ray—arrow indicates electrode in a satisfactory position.

Methods

A Medline database search was performed for all English publications using the words “aural atresia”, “Cochlear implant” and “microtia”. Articles were included if they described patients with congenital AA and/or microtia who had a CI. Articles were included if the patients with AA or microtia could be reviewed separately from patients with hearing loss of other etiologies. They are summarized in Table 1.

Table 1.

Literature review: Cases of cochlear implantation performed in patients with microtia and/or aural atresia.

	Author	Age/sex	Side	External ear	Ossicles	Facial nerve	Cochlear implant	Electrode insertion via	Outcome	Complications
1	Lin (2005) 2	2/M	R	Grade III microtia, aural atresia	Dysplastic malleus and incus, stapes fixation	Inferior and posteriorly positioned FN	Cochlear nucleus 24 contour	Cochleostomy anterior to RW dimple	Ling 6 sounds between 35–50 dB	No
2	Celenk (2015) 3	4/F	L	Aural atresia	Dysplastic ossicles	Anteriorly displaced FN	Medel (pulsar)	RW	SAT 30 dB LiP test 100%	No
3	Bernardeschi (2015) 4	56/NA	R	Aural atresia	NA	NA	Advanced bionics HiRes90K	NA	NA	No
4	Castellino (2020) 5	4/F	R	Bilateral microtia, L EAC atresia	Single dysmorphic ossicles	Anteriorly displaced FN	NA	Cochleostomy	NA	Misplacement of electrodes in posterior SCC
5	Wong (2021) 6	4/F	R	Bilateral microtia, aural atresia	Malformed incudo-stapedial complex	Anterior displaced 2nd genu, shortened AP diameter of tympanic FN	Advanced bionics slim J	Cochleostomy	Ling 6 sounds between 35–50 dB	No
6	Current case	8/M	R	Grade III microtia, aural atresia	Fused malleo-incudal complex	Anteriorly displaced FN	Advanced bionics HiRes 90K advantage	Cochleostomy	3 months post-op: Right aided thresholds 30–40 dB Able to detect ling 6 sounds at 2 m	No

AP: anterior-posterior, EAC: external acoustic canal, F: female, FN: facial nerve, L: left, M: male, NA: not available, R: right, SAT: speech awareness test, SCC: semi-circular canal.

Only 5 other cases described patients who had microtia and/or AA who had CIs. Case 1 had both microtia and AA, ² cases 2 ³ and 3 ⁴ had AA alone, without microtia. Case 4 had bilateral microtia, and only the contralateral ear was atretic. ⁵ Case 5 had bilateral complete AA and grade 3 microtia with right facial paresis ⁶ (Table 1).

Case 4 had Goldenhar Syndrome. Case 2 had hypertelorism and saddle nose, but no formally diagnosed syndrome. Electrode misplacement into the posterior semicircular canal occurred in Case 4. No other complications were encountered.

Discussion

Severe SNHL is rare in microtia and AA. Hearing rehabilitation options are mainly focused on augmentation of conductive hearing loss. However, CI is a viable option for patients with microtia and AA with severe SNHL, though adequate planning is required prior to surgery.

Pre-operative considerations

Microtia and AA are commonly associated with aberrant facial nerve anatomy and dysplastic ossicles. ⁷ An anatomic study by Goldsztein et al. described facial nerve dehiscence in 53% of cases, most commonly at the tympanic segment. Also, facial nerve-stapes contact was identified in 11%. ⁸ Takegoshi et al. described that the mastoid segment of the facial nerve was 3 mm more anterior in patients with microtia. The angle between the tympanic and mastoid segments was about 20° more obtuse, due to a shorter tympanic segment. ⁹ The authors highlight that both HRCT and MRI should be performed. HRCT aids in identifying the course of the facial nerve, middle ear structures and cochlear anatomy. MRI confirms the presence of the cochlear nerves. In this case, bilateral cochlear nerves were hypoplastic on MRI. Other considerations include the presence of other cochleovestibular anomalies, or an enlarged cochlear or vestibular aqueduct which may increase the risk of a cerebrospinal fluid (CSF) leak. ¹⁰ Vascular anomalies such as an anteriorly displaced sigmoid and a high riding jugular bulb may impede access to the facial recess. ¹⁰

The right ear was selected despite the prolonged auditory deprivation as this was the poorer hearing ear and the parents wanted to retain the current hearing on the aided left ear. They opted for a unilateral CI that could sync with the HA (Phonak Naida™ Link), allowing bimodal stimulation. Depending on the patient’s progress and if there was progressive hearing loss, a CI may be considered for the left ear in future. Additionally, although bilateral CIs are known to have significant benefit over a unilateral CI, bilateral CI users may exhibit less than or similar levels of binaural summation compared to patients with bimodal hearing. This is believed to be because each ear provides complementary information—i.e. the electrical signals from the CI are the base for understanding speech but the acoustic signals in the non-implanted ear provides a more natural sound and other non-electrical cues. ¹¹

Intra-operative considerations

Incision placement was decided in discussion with a facial plastics surgeon. There is wide variability in the blood supply of microtic auricles. Necrosis of the overlying skin and exposure of the cartilaginous framework may result from a poorly vascularized skin pocket. ¹² Hence, the incision was placed approximately 2 cm posterior to the edge of where the normal pinna would be if buried under the skin, so as not to compromise the vascularity of the skin. Lin et al. similarly described a large C-shaped incision made within the hairline. ²

Facial nerve monitoring is crucial in patients with abnormal anatomy. While HRCT is helpful, intra-operative findings may differ especially when the mastoid is opacified. ¹³ Intra-operative facial nerve monitoring is adopted routinely in all CIs in our institution. Up to 53% of cases with AA were found to have intra-operative facial nerve dehiscence. ⁸ Other techniques described included electromagnetic navigation system Digipointeur, continuous facial nerve stimulating burr ⁴ and image-guided navigation system. ⁶

Various approaches for access included a conventional transmastoid facial recess approach, ² canal wall down mastoidectomy and mastoid cavity obliteration with abdominal fat ⁴ and subtotal petrosectomy with blind sac closure. ⁵ Castellino et al. cited that the approach allowed better visualization compared to the traditional facial recess approach and provided a closed safe cavity as middle ear effusions are common in patients with associated deformities e.g. palatal abnormalities. ⁵ In our case, the atretic plate was drilled to access the middle ear directly, using the middle fossa as a landmark. The removal of the malleo-incudal complex further allowed better access for the cochleostomy.

Post-operative considerations

As the microtia ear is too small to hold the behind-the-ear (BTE) processor, it is clipped to his clothes. The microphones on the processor are turned off to avoid excessive noise from the clothes rubbing against them. The headpiece microphone is activated to pick up speech and environmental sounds. If the patient undergoes pinna reconstruction in future, he can use the BTE processor on his right ear by activating the processor’s microphones. Off-the-ear processors are also an option for patients who cannot wear the processor on their pinna.

Finally, the family was counselled extensively on the need for AVT post-surgery. Multiple social and environmental factors influence development of language skills in hearing impaired children including earlier intervention with HAs and maternal engagement. ¹⁴ Children who had AVT significantly outperformed those who had standard rehabilitation in speech and language performance. ¹⁴

This case report illustrates the technical challenges in implanting a patient with profound hearing loss with microtia and AA. To our knowledge, this is the third case with both AA and microtia who had undergone CI. The spectrum of deformity may be diverse in congenital AA and microtia. Different ossicular anomalies and facial nerve configurations may exist. Hence, these considerations should be assessed at outset and the patient and family should be counselled appropriately.

Conclusion

CI is a viable option for patients with severe to profound SNHL in patients with microtia and AA. However, as the configuration of the ears and critical structures may be more anatomically diverse, careful planning and extensive counselling should be undertaken prior to surgery.