The aim of this 2-part review was to highlight the role that imaging plays in the management of childhood sensorineural hearing loss, which is among the most prevalent chronic conditions encountered in the pediatric age group, and to review the imaging features of some of the more common causes of childhood hearing loss. Although identifiable abnormalities are seen in few children with hearing loss on CT and MRI, imaging remains an important part of the diagnostic work-up, particularly when cochlear implantation is being considered. Information that can only be provided by imaging includes the presence and severity of inner ear malformations, the integrity of the cochlear nerve, and the presence of significant cochlear ossification, all of which are critical for determining surgical candidacy, device selection, and surgical approach.

Much of Part 1 of the series focused on the classification of inner ear anomalies, which was first proposed by Sennaroglu and Saatchi in 2002.¹ More recently, Sennaroglu and Bajin revised the classification system to incorporate several entities that were not previously accounted for.² This newly proposed system now includes 8 distinct groups of inner ear malformations, each with several subtypes. Modifications include the addition of entities such as rudimentary otocysts, incomplete partition type III (also commonly referred to as the X-linked stapes gusher), and cochlear aperture anomalies to the classification system. In addition, an enlarged vestibular aqueduct without associated abnormalities of the cochlea, vestibule, and semicircular canals receives its own category. Those who are interested are encouraged to read their article, which also describes issues related to cochlear implantation for each type of malformation.

The second part of the series focused primarily on some of the more commonly encountered syndromic forms of sensorineural hearing loss. To date, there are roughly 400 reported syndromes that list hearing loss as a clinical feature.³ In many of these syndromes, hearing loss is an inconstant feature, and many syndromes demonstrate no obvious abnormalities on imaging.

In select cases, however, the findings provided by imaging may provide clues to the underlying genetic basis of the disease or prompt a search for syndrome-defining anomalies elsewhere in the body. As such, radiologists who interpret temporal bone imaging studies in the pediatric population should be well versed in the spectrum of commonly encountered syndromes and inner ear malformations.

Unfortunately, the techniques available in our current toolbox for temporal bone imaging remain fairly crude and reveal only the surface of what is actually going on in the ears of children with deafness. CT only shows us the configuration of the bony labyrinth from which we can occasionally infer the presence of underlying membranous or cochlear nerve abnormalities, while the resolution of currently available MRI techniques remains too low to provide much information beyond the status of the fluid containing inner ear cavities and the cranial nerves. We are still unable to reliably visualize the microscopic structures of the membranous labyrinth and the organ of Corti.

Though not without its own challenges, imaging at 7T has shown promise when compared with imaging at 3T in improving the visualization of many delicate inner ear structures such as the scala media,⁴ and research on temporal bone imaging with ultra-high-field MRI is also ongoing.⁵ While we are not there yet, it is not difficult to envision a point in the future at which we will be able to visualize and noninvasively explore the exquisite microarchitecture of the inner ear and resolve the microscopic alterations associated with individual gene malformations.

Click here to read Part 1 and Part 2...

References

1. Sennaroglu L, Saatchi I. A new classification for cochleovestibular malformations. Laryngoscope 2002;112:2230–41, 10.1097/00005537-200212000-00019.
2. Sennaroglu L, Bajin MD. Classification and current management of inner ear malformations. Balkan Med J 2017;34:397–411, 10.4274/balkanmedj.2017.0367.
3. Castiglione A, Busi M, Martini A. Syndromic hearing loss: an update. Hearing, Balance and Communication 2013;11:146–59, 10.3109/21695717.2013.820514.
4. van der Jagt MA, Brink WM, Versluis MJ, et al. Visualization of human inner ear anatomy with high-resolution MR imaging at 7T: initial clinical assessment. AJNR Am J Neuroradiol 2015;36:378–83, 10.3174/ajnr.A4084.
5. Thylur DS, Jacobs RE, Go JL. Ultra-high-filed magnetic resonance imaging of the human inner ear at 11.7 Tesla. Otol Neurotol 2017;38:133–38, 10.1097/MAO.0000000000001242.