Genetics of Inner Ear Malformations: A Review

Abstract

Inner ear malformations are present in 20% of patients with sensorineural hearing loss. Although the first descriptions date to the 18th century, in recent years the knowledge about these conditions has experienced terrific improvement. Currently, most of these conditions have a rehabilitative option. Much less is known about the etiology of these anomalies. In particular, the evolution of genetics has provided new data about the possible relationship between inner ear malformations and genetic anomalies. In addition, in syndromic condition, the well-known presence of sensorineural hearing loss can now be attributed to the presence of an inner ear anomaly. In some cases, the presence of these abnormalities should be considered as a characteristic feature of the syndrome. The present paper aims to summarize the available knowledge about the possible relationships between inner ear malformations and genetic mutations.

Keywords: cochlear aplasia; cochlear hypoplasia; common cavity; complete labyrinthine aplasia; genetics; hearing loss; incomplete partition; inner ear malformations; posterior labyrinth.

Figure 1

Cone beam CT imaging of a common cavity deformity (white asterisk). Note that the axis of the internal auditory canal (white arrow) seems to divide the cochleovestibular structure into anterior and posterior parts. This characteristic makes the common cavity different from the cochlea aplasia with dilated vestibule.

Figure 2

CT imaging of a cochlear aplasia with dilated vestibule. In contrast with a common cavity, the whole cochleovestibular structure is behind the axis of the internal auditory canal (white arrow).

Figure 3

Schematic drawings of the three different types of incomplete partitions.

Figure 4

CT imaging of a bilateral incomplete partition type 1. The anterior (cochlear) and posterior (vestibular) parts of the inner ear are clearly distinguishable, with the cochlear portion being cystic and almost normal in terms of size.

Figure 5

CT imaging of a left incomplete partition type 2. In this malformation the middle and apical turns appear to be fused (white arrowhead). Frequently, an enlarged vestibular aqueduct is also detectable (white arrow).

Figure 6

CT imaging of a bilateral incomplete partition type 3. The cochlear structures appear to be symmetrically altered, with the typical appearance of an empty cochlea, without a clear fundus of the internal auditory canal.