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

Abstract

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.