Classification of Third Mobile Window Anomalies

Abstract

While superior semicircular canal dehiscence (SSCD) is relatively well-known in the medical community, there are many other sites of otic capsule dehiscence (OCD) which create a third mobile window resulting in third window syndrome (TWS). Over the past quarter century, there has been tremendous expansion of the depth of our knowledge and understanding of TWS; however, the identification of lesser-known sites of OCD remains an important diagnostic and therapeutic challenge. This is all the more so as in our experience TWS, including SSCD, remains under-diagnosed. Therefore, the development of a unitary anatomical-clinical and radiological classification would be an important step for a better understanding of these pathologies by neurotologists, otologists, neurologists, auditory-vestibular specialists, otolaryngologists, and neuroradiologists. Thus, the probability of being left without an etiological diagnosis in case of “mysterious” pseudo-conductive hearing loss, with or without obvious associated vestibular phenomena, should become lower. Furthermore, due to the progressive increase in new reported variants of OCD, the characterization of the anatomical structures involved, as well as the size and location of the TW, has become essential for a better understanding of the various mechanisms associated with this pathology. This allows us not only to systematize the different known variants but also to propose new, eventually less invasive or more pathophysiological therapeutic strategies. Based on the experience of the authors of this chapter, who have considered not only personal case studies but also other relevant publications on the subject, this chapter is the result of collaborative collegial work.