Histopathologic findings in inner ear malformations

For years, the term "Mondini dysplasia" was used to describe virtually every type of congenital inner ear malformation detected in imaging tests. More recently, histopathologic and imaging studies led to the description of several novel morphologic features, which were categorized into new groups according to morphologic patterns of the inner ear abnormalities. In addition, those new findings made possible to hypothesize potential pathophysiologic and embryogenic mechanisms involved in the genesis of each specific type of malformation. However, there are still obscure areas that still need to be better understood, such as quantitative and qualitative pathologic changes in the cellular, sensorial, and neural elements in the inner ear of patients with inner ear abnormalities. Therefore, histologic analysis of human temporal bones from patients who had inner ear malformations constitutes a tool of invaluable value. The clinical impact of past studies involving inner ear malformations is clear: today, cochlear implants or auditory brainstem implants are well indicated to treat hearing loss in patients with inner ear malformations, who were previously excluded from candidacy criteria. In the future, a broader understanding of yet obscure aspects of those malformations may increase even further the candidacy for those implants and create strategies for improved functional results. Thus, the objective of this chapter is to report, based on a review of the literature, otopathologic findings in human temporal bones from donors with inner ear malformations and to correlate the findings with embryogenic factors and their clinical implications.