Vestibular dysfunction after cochlear and auditory brainstem implantation: Madras ENT Research Foundation experience

<p><strong>Background:</strong> Cochlear implantation is an established procedure for patients with bilateral severe to profound sensorineural hearing loss. CI may, in some implantees, have a detrimental impact on vestibular function. Auditory brainstem implantation is a safe and effective procedure in children with bilateral cochlear and cochlear nerve aplasia. The aim of the study was to assess the impact of cochlear implantation and auditory brainstem implantation on the vestibular function.</p><p><strong>Methods:</strong> Three hundred and twenty patients who underwent CI surgery over a four years period from November 2016 to November 2020 were studied for symptoms of vestibular disturbance. Twenty three patients complained of giddiness and underwent vestibular function testing including videooculography, caloric test and vestibular evoked myogenic potentials. 48 patients with cochlear and cochlear nerve aplasia underwent ABI surgery from September 2009 to March 2019. The correlation between the size of the flocculus and the presence of vestibular symptoms was studied.</p><p><strong>Results: </strong>After CI, vestibular disturbances were seen in 23 patients (7.2%) and were transient. In auditory brainstem implantees, vestibular disturbances were seen in eight patients (16.7%) and were found to correlate with the size of the cerebellar flocculus.<strong></strong></p><p><strong>Conclusions: </strong>Vestibular disturbances are rare after cochlear and auditory brainstem implant surgery. During CI, the preservation of vestibular function should be attempted using minimally invasive techniques. ABI surgery requires meticulous dissection, especially of a large cerebellar flocculus to minimize the possibility of vestibular disturbances.<strong></strong></p>

A Case of Cochlear Implantation in a Child with Congenital Aural Atresia and Cochlear and Cochlear Nerve Malformation

Congenital aural atresia (CAA) is usually accompanied by an anomalous course of facial nerves, which may run over the round window niche toward the promontory in some cases of CAA. Very rarely, cochlear malformation might coexist at the same ear which has CAA, in which case cochlear implantation can be difficult due to anomalous facial nerve. Herein we present a case of cochlear implantation performed in a child who had CAA along with cochlear hypoplasia and cochlear nerve aplasia. The mastoid segment of facial nerve was displaced anteriorly, running over the round window niche. The surgery was done successfully using the round window approach without facial nerve injury.

Autosomal Dominantly Inherited GREB1L Variants in Individuals with Profound Sensorineural Hearing Impairment

Congenital hearing impairment is a sensory disorder that is genetically highly heterogeneous. By performing exome sequencing in two families with congenital nonsyndromic profound sensorineural hearing loss (SNHL), we identified autosomal dominantly inherited missense variants [p.(Asn283Ser); p.(Thr116Ile)] in GREB1L, a neural crest regulatory molecule. The p.(Thr116Ile) variant was also associated with bilateral cochlear aplasia and cochlear nerve aplasia upon temporal bone imaging, an ultra-rare phenotype previously seen in patients with de novo GREB1L variants. An important role of GREB1L in normal ear development has also been demonstrated by greb1l−/− zebrafish, which show an abnormal sensory epithelia innervation. Last, we performed a review of all disease-associated variation described in GREB1L, as it has also been implicated in renal, bladder and genital malformations. We show that the spectrum of features associated with GREB1L is broad, variable and with a high level of reduced penetrance, which is typically characteristic of neurocristopathies. So far, seven GREB1L variants (14%) have been associated with ear-related abnormalities. In conclusion, these results show that autosomal dominantly inherited variants in GREB1L cause profound SNHL. Furthermore, we provide an overview of the phenotypic spectrum associated with GREB1L variants and strengthen the evidence of the involvement of GREB1L in human hearing.

Cochlear Nerve Hypoplasia: Audiological Characteristics in Children and Adults

Background: Cochlear nerve deficiency is a general term used to describe both cochlear nerve hypoplasia (CNH) and cochlear nerve aplasia. Although these two conditions can have similar results on audiological evaluation, CNH yields more variation in audiological tests. Objectives: To describe the audiological characteristics of the CNH cases in our series in relation to radiological findings. Methods: We reviewed the medical charts, audiological findings, and radiological findings on cases with CNH. We included cases with CNH in one ear or both ears. Out of 90 subjects with CNH, we included a total of 40 individuals (21 women and 19 men; 49 ears) in the current study. We reviewed and analyzed the participants’ audiological test results according to the radiological findings. Results: Cases with CNH showed variations according to the cochlear structure. There were 13 normal cochleae, 4 with incomplete partition type I, and 32 with cochlear hypoplasia. The accompanying cochlear apertures also showed variation: 17 were normal, 28 stenotic, and 4 aplastic cochlear apertures. The subjects displayed hearing loss ranging from moderate to profound; furthermore, 4 subjects had no response to sound whatsoever. The degree of hearing loss was not statistically significantly different with regard to the presence or absence of cochlear malformation with CNH (p > 0.005). We observed both sensorineural hearing loss and mixed-type hearing loss among the CNH cases. Conclusions: CNH is the presence of a cochlear nerve that is smaller in diameter than the facial nerve. It can be accompanied with other associated inner ear malformations of different degrees of severity. We observed degrees of hearing loss ranging from moderate to profound.

Cochlear Nerve Aplasia with Detectable Olivocochlear Efferent Function: A Distinct Presentation of Auditory Neuropathy Spectrum Disorder

Background: Cochlear nerve aplasia (CNA) may present with features of auditory neuropathy spectrum disorder (ANSD), having detectable otoacoustic emissions (OAE) but profound hearing loss. We propose that some children with CNA have a distinct form of afferent ANSD in which efferent cochlear nerve function can be detected using contralateral suppression of OAE. Methods: Children were prospectively enrolled with MRI and auditory brainstem response evidence of unilateral CNA, a normal contralateral ear, and detectable OAE bilaterally. Distortion product OAE (DPOAE) levels were recorded in real time with default primary tone settings: frequency (f)2 = 4.5 kHz and f2/f1 = 1.22 kHz, with level (L)1 = 65 dB SPL and L2 = 55 dB SPL. Recordings were made over 2 min with simultaneous application of an intermittent contralateral broadband noise (CBBN) stimulus at 60 dB SPL. Results: Three girls, aged 4.5, 7, and 8 years, participated. Suppression of DPOAE of 0.15–1.3 dB was detected in all 3 ears with CNA in response to CBBN stimulation. No response was detected in the normal ears. Conclusions: Children with unilateral ANSD can have normal efferent cochlear nerve function despite MRI evidence of ipsilateral CNA. The importance of these findings for newborn hearing screening and cochlear implantation is discussed.

Unilateral auditory neuropathy spectrum disorder: retrocochlear lesion in disguise?

Objective:To investigate whether the aetiology for hearing impairment in neonates with unilateral auditory neuropathy spectrum disorder could be explained by structural abnormalities such as cochlear nerve aplasia, a cerebellopontine angle tumour or another identifiable lesion.Methods:In this prospective case series, 17 neonates were diagnosed with unilateral auditory neuropathy spectrum disorder on electrophysiological testing. Diagnostic audiology testing, including auditory brainstem response testing, was supplemented with computed tomography and/or magnetic resonance imaging.Results:Ten of the neonates (59 per cent) showed evidence for cochlear nerve aplasia. Of the remaining seven, four were shown to have another abnormality of the temporal bone on imaging. Only three neonates (18 per cent) were not diagnosed with cochlear nerve aplasia or another lesion. Three computed tomography scans were reported as normal, but subsequent magnetic resonance imaging revealed cochlear nerve aplasia.Conclusion:Auditory neuropathy spectrum disorder as a unilateral condition mandates further investigation for a definitive diagnosis. This series demonstrates that most neonates with unilateral auditory neuropathy spectrum disorder had pathology as visualised on computed tomography and/or magnetic resonance imaging scans. Magnetic resonance imaging is an appropriate first-line imaging modality.

Cochlear implant: what the radiologist should know

Cochlear implant is the method of choice in the treatment of deep sensorineural hypoacusis, particularly in patients where conventional amplification devices do not imply noticeable clinical improvement. Imaging findings are crucial in the indication or contraindication for such surgical procedure. In the assessment of the temporal bone, radiologists should be familiar with relative or absolute contraindication factors, as well as with factors that might significantly complicate the implantation. Some criteria such as cochlear nerve aplasia, labyrinthine and/or cochlear aplasia are still considered as absolute contraindications, in spite of studies bringing such criteria into question. Cochlear dysplasias constitute relative contraindications, among them labyrinthitis ossificans is highlighted. Other alterations may be mentioned as complicating agents in the temporal bone assessment, namely, hypoplasia of the mastoid process, aberrant facial nerve, otomastoiditis, otosclerosis, dehiscent jugular bulb, enlarged endolymphatic duct and sac. The experienced radiologist assumes an important role in the evaluation of this condition.