Mondini Dysplasia, (Mondini malformation, Mondini defect) is an abnormality in the inner ear that can be the cause of hearing loss.

A person with Mondini dysplasia has a cochlea that is incomplete. A normal cochlea has two and a half turns, a cochlea with Mondina dysplasia has two, one and a half, one, or no turns (or increments). This results in gradual or even sudden hearing loss that may be profound."case history". http://www.jpgmonline.com/article.asp?issn=0022-3859;year=2001;volume=47;issue=4;spage=272;epage=3;aulast=Shah. 

This type of malformation has been described as a flattened cochlea with development only of the basal Coil. Instead of two and one-half turns in the bony cochlea, there may be only one and one-half turns, with the middle and apical turns occupying a common space or cloaca. The agenesis is rarely symmetrically bilateral, but the other ear always shows some degree of malformation. The vestibular structures and their associated neural elements may be similarly underdeveloped. There appears to have been an interruption in the development of the cochlea at the stage in which it is represented by a short, curved tube (about the 6th week of gestation).

Vestibular structures may be recognizable in some cases; in others there is no membranous labyrinth. Occasionally some sensory epithelium may be present; this implies the possibility of function. An enlarged endolymphatic duct and sac and a deficient utriculoendolymphatic valve are commonly found associated with collapse of Reissner’s membrane or an absence of endolymphatic hydrops. Lesions of the end-organ of Corti may be present or absent. The stria vascularis and spiral ligament are often normal. Mondini’s deformity may be associated with an absence of the oval and round windows along with other aplastic lesions of the middle ear.

The Mondini type of deafness may first become manifest in childhood or early adult life. Auditory function ranges from marked deafness to normal hearing. Mechanisms of hearing loss in Mondini’s aplasia may be explained on the basis of pathologic findings in the inner or middle ears, including dysgenesis of the end organs and associated neural elements sufficient to cause a sensorineural hearing loss ; aplasia or the oval or round windows, which might explain manifest sensorineural hearing loss in the presence of normal-appearing organs of Corti; and aplasia or infection of the middle ear causing a conductive loss.²

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Mondini Dysplasia

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