Auditory neuropathy spectrum disorder (ANSD) generally presents with normal outer hair cell function evidenced through OAEs and/or cochlear microphonics, in tandem with absent ABR. Roche et al (2010) note that ANSD is a syndrome with significant discrepancies between measures of cochlear function and more central locations within the auditory system. Roche et al report that when evaluating the otic capsule, CT and MRI each have their advantages. For example, CT is superior when assessing the intratemporal section of the facial nerve, inner ear ossification and temporal bone pathology. However, MRI provides better definition of soft tissues proximal to the ear, such as the cochlear nerve and the brain.
Roche et al reported on 118 children with ANSD who had either CT or MRI (or both) imaging studies available for a retrospective review. Twenty-eight of the children had unilateral ANSD and 90 children had bilateral ANSD, thus, 208 ears with ANSD were reported. Fifty-eight percent of the children were male, 42 percent were female. The majority of children were white and African American.
No significant medical histories (beyond ANSD) were found in 25 percent of the children. Pre-maturity was the most common historical finding across all children with ANSD occurring in 42 percent of the children. Thirty-eight percent of the children with ANSD were admitted to the NICU during the post-natal period, 27 percent had mechanical ventilation and hyperbilirubinemia was diagnosed in 20 percent. Thus, children who presented with bilateral ANSD had a wide range of risk factors (prematurity, NICU admission, mechanical ventilation, and hyperbilirubinemia).
With regard to radiographic imaging findings, nearly 65 percent of the MRIs revealed at least one abnormality and 41 percent demonstrated two or more abnormalities. CT revealed 55 percent with at least one abnormality and 45 percent with two or more abnormalities. Consistent with previous reports, Roche et al noted that the normal measured internal auditory canal (IAC) diameter of 3 mm was used as their standard, and noted 27 percent of the IACs evaluated were smaller, while 73 percent were 3 mm. Additionally MRI revealed 16 percent of the 106 brains evaluated had prominent temporal horns, 19 percent had cerebrospinal fluid and/or ventricular abnormalities, 15 percent had brainstem/cerebellum abnormalities, and 15 percent had white matter changes and more (see page 784, Table 3).
MRI revealed a surprisingly high incidence (28 percent) of cochlear nerve deficiency (CND) and other positive CNS findings (see above) in these children. Indeed, 42 of the 106 MRIs of children with ANSD had multiple intracranial findings beyond CND. Roche et al concluded that MRI is justified as the initial “imaging study of choice” for children with ANSD.
For More Information, References, and Recommendations
Roche JP, Huang BY, Castillo M, Bassim MK, Adunka OF, Buchman CA. (2010) Imaging Characteristics of Children with Auditory Neuropathy Spectrum Disorder. Otology & Neurotology 31(5):780–788.