Unilateral Auditory Neuropathy Caused by Cochlear Nerve Deficiency

Abstract

Objective. To explore possible corelationship between the cochlear nerve deficiency (CND) and unilateral auditory neuropathy (AN). Methods. From a database of 85 patients with unilateral profound sensorineural hearing loss, eight who presented with evoked otoacoustic emissions (EOAEs) or cochlear microphonic (CM) in the affected ear were diagnosed with unilateral AN. Audiological and radiological records in eight patients with unilateral AN were retrospectively reviewed. Results. Eight cases were diagnosed as having unilateral AN caused by CND. Seven had type “A” tympanogram with normal EOAE in both ears. The other patient had unilateral type “B” tympanogram and absent OAE but CM recorded, consistent with middle ear effusion in the affected ear. For all the ears involved in the study, auditory brainstem responses (ABRs) were either absent or responded to the maximum output and the neural responses from the cochlea were not revealed when viewed by means of the oblique sagittal MRI on the internal auditory canal. Conclusion. Cochlear nerve deficiency can be seen by electrophysiological evidence and may be a significant cause of unilateral AN. Inclined sagittal MRI of the internal auditory canal is recommended for the diagnosis of this disorder.

Diverse etiologies manifesting auditory neuropathy characteristics from infants with profound hearing loss and clinical implications

“…We did not restrict our analysis to either the unilateral or bilateral profound HL. A couple of studies have reported AN characteristics in association with CND [14,15]. However, an overall underlying etiologic distribution of AN characteristics could not be drawn since these studies addressed only unilateral cases [14,15].…”

“…A couple of studies have reported AN characteristics in association with CND [14,15]. However, an overall underlying etiologic distribution of AN characteristics could not be drawn since these studies addressed only unilateral cases [14,15]. To overcome this shortcoming, our current study employed a cohort encompassing both unilateral and bilateral profound HL, consecutively recruited during the study period.…”

Potential benefits from cochlear implantation of children with unilateral hearing loss

“…Of these, 50% were unilateral (all moderate to severe losses). Auditory neuropathy spectrum disorder (ANSD) is unilateral in about 25% of cases (Teagle et al, 2010;Liu et al, 2012). Dedhia et al (2013) investigated a series of 78 children who passed neonatal screening but were subsequently diagnosed with a hearing loss during childhood; 47% were severe or profound and 26% were unilateral.…”

“…Clemmens et al (2013) assessed 134 children identified with sensorineural UHL using magnetic resonance imaging (MRI) and CT. Cochlear nerve deficiency (CND) was present in 26% overall, but increased to 48% in cases of severe-profound deafness, and 100% in infants (n = 10) and was strongly predicted by narrow (<1.7 mm) BCNC. The clinical presentation of CND overlaps with that of ANSD, and it has become apparent that a high proportion of unilateral ANSD cases are associated with CND (Teagle et al, 2010, Liu et al, 2012.…”

“…However, it is particularly important that assessment of potential recipients includes radiological imaging of the temporal bones, including IAC, as a relatively high proportion of unilateral sensorineural losses are associated with structural cochlear and IAC abnormalities (Song et al, 2009, Clemmens et al, 2013Masuda et al, 2013), which are known to produce a relatively poor percept from a CI (Young et al, 2012;Vincenti et al, 2014). It should also be noted that cases diagnosed with unilateral ANSD are often associated with CND (Teagle et al, 2010;Liu et al, 2012). While positive outcomes have been reported for implantation of subjects with bilateral ANSD (Berlin et al, 2010;Teagle et al, 2010), it is not yet clear whether this also applies to unilateral cases, though it seems likely that it should, as outcomes from cochlear implantation in ANSD have been shown to be comparable to those in subjects with sensorineural losses as long as the cochlear nerve is intact (Rance and Barker, 2009).…”