**4. The olivocochlear pathway**

30 Hearing Loss

**Wave I Action potential arising from afferent activity of cochlear nerve** 

**Wave II Action potential arising from proximal cochlear nerve entering** 

**Wave III Arise from second order neurons beyond the cochlear nerve in the** 

**Wave V Multiple anatomic origins postulated in the vicinity of the inferior** 

**Wave IV Arise from third order neurons located in the superior olivary complex** 

One disorder that continuously eludes the new born hearing screen is ANSD. ANSD represents a range of hearing disorders of variable severity which present with pure tone hearing thresholds that may be low or approach normal, but underestimate the subject's perception of hearing difficulty. Included within the spectrum are inner hair cell anomalies, neuropathy of the auditory nerve, disruption of the olivocochlear response (OCR), and brainstem dysfunction that can be secondary to kernicterus (Amatuzzi et al., 2001; Berlin et al., 2005; Harrison, 1998; Hood & Berlin, 2001; Shapiro, 2003; Starr, Picton, Sininger, Hood, & Berlin, 1996; Yasunaga et al., 1999).The unifying feature of ANSD diseases are a characteristic finding of abnormal ABR waveforms in the presence of normal OAE and/or cochlear microphonic (CM). Middle ear muscle reflexes and the olivocochlear reponse are also absent. These findings are suggestive of persistent outer hair cell activity but lack of a normal afferent auditory pathway and as such would be missed by currently employed screening methods (Manchaiah et al., 2011). Accurate diagnosis is hampered by the lack of a simple commercially available test for OCR function but typically the diagnosis can be

Etiologies of ANSD that have been identified include polyneuropathy (especially in adults), perinatal anoxia and hypoxia, and hyperbilirubinaemia, congenital brain anomalies, ototoxic drug exposure, and genetic factors. An estimated 40% of cases have an underlying genetic basis, which can be inherited in both syndromic and non-syndromic conditions

Treatment options in ANSD include auditory verbal therapy, cued speech, hearing aids and cochlear implantation (Cone-Wesson, Rance, & Sininger, 2001; Rance & Barker, 2008a; Hood & Berlin, 2001). Prognostication and predicting treatment outcome is difficult and varies depending on origin. Some forms of neonatal ANSD can show significant spontaneous

(Harrison, 2001; Manchaiah et al., 2011; Nadol Jr, 2001; Starr et al., 1996).

**entering internal auditory canal** 

**brainstem** 

**colliculus** 

assumed from OAE and ABR results alone.

**cochlear nucleus** 

**Wave VI Arise from medial geniculate body** 

**Wave VII Arise from medial geniculate body** 

Table 4. Characteristic auditory brainstem response waves

**3. Auditory neuropathy spectrum disorder (ANSD)** 
