Enlarged vestibular aqueduct syndrome-dehiscence syndromes-honeycomb mastoid Pathophysiology and evidence for clinical differentiation

Background Differential diagnosis of dizziness with hearing loss requires standardized procedures for detection and classification of rare congenital and acquired malformations of the petrous part of the temporal bone. Objective The aim of this study was to present the physiology and pathophysiology of endolymphatic and perilymphatic pressure regulation, diagnostic guidelines, and aspects of prognosis and treatment. Materials and methods Relevant publications and guidelines were evaluated and own cases are reported. Results Enlarged vestibular aqueduct (EVA) is the most frequently observed malformation of the inner ear, which leads to increased internal hydrostatic pressure and cochleovestibular dysfunction. Non-syndromic and syndromic forms, e.g., Pendred syndrome, are known. Other pressure-relevant malformations are semicircular canal dehiscence syndrome (SCDS) and enlargement of the cochlear aqueduct. There are currently no treatment options for EVAS and enlarged cochlear aqueduct. Pendred syndrome generally requires treatment with cochlea implants (CI) in early childhood. Dizziness and autophony in patients with SCDS syndrome can be effectively treated by semicircular canal occlusion and coverage. Conclusion Complaints in non-syndromic EVA and SCD syndrome are mainly caused by exposure of the inner ear to provoked and spontaneous pressure increases. Deafness and vestibular dysfunction in syndromic EVA (i.e., Pendred syndrome, branchiootorenal syndrome) are caused by malformation of the cochlea, genetic maldevelopment of the hair cells, and pressure effects.