Vestibular anomalies and dysfunctions in children with inner ear malformations: A narrative review

Abstract

About 20% of children with congenital hearing loss present malformations of the inner ear. In the past few years much has been understood about the morphology and function of the anterior part of the labyrinth, since hearing loss may have a dramatic effect on the overall development of a child. Nowadays, for most of them, a chance for hearing rehabilitation is available, making hearing loss a treatable condition. The anomalies range from the lack of development of the whole inner ear to specific anomalies of isolated structures. Despite the frequent concomitant involvement of the posterior part of the labyrinth, this part of the inner ear is frequently neglected while discussing its morphology and dysfunction. Even though vestibular and balance function/dysfunction may have a significant impact on the global development of children, very little is known about these specific disorders in patients with inner ear malformations. The aim of this review is to summarize the available literature about vestibular anomalies and dysfunctions in children with inner ear malformations, discussing what is currently known about the topic.

Keywords: balance; hearing loss; inner ear malformations; motor development; vestibular function.

Figure 1

Flowchart for the identification of the studies in Pubmed database.

Figure 2

Drawings of inner ear structures in coronal view. (A) Normal anatomy. See in light yellow the bone labyrinth. (B) Drawing of total labyrinthine aplasia. Note the absence of the whole inner ear. (C) Drawing of a rudimentary otocyst, in which a single ovid cavity, representing the cochlear and vestibular part of the inner ear is within the otic capsule, without any communication with any internal auditory canal. (D) Drawing of a common cavity, a single cavity communicating with the internal auditory canal which presents a common cochleovestibular nerve.

Figure 3

Bone-CT (A) and T2 weighted-MRI (B) imaging of a right cochlear aplasia. Note the complete development of the cystic cavity behind the axis of the internal auditory canal (dashed white line). The posterior labyrinth is cystic and it also represents the semicircular canals (asterisks).

Figure 4

Drawings of inner ear structures showing both the auditory/anterior part (with an open cochlea) and the vestibular/posterior part. (A) Normal anatomy. See in gray the membranous labyrinth, with the endolymphatic sac with its sac-like shape, in light blue the scala tympani, in orange the scala vestibuli. (B) Drawing of enlarged vestibular aqueduct with the enlarged endolymphatic sac (in gray). (C) Drawing of a malformation in which there is the concomitant presence of the enlarged endolymphatic sac (in gray) and an incomplete partition type II, with the middle and apical turn (in green) of the cochlea are fused. (D) Drawing of an incomplete partition type I in which the cochlea is of normal dimensions but cystic, with the malformed posterior part of the labyrinth. (E) Drawing of an incomplete partition type III, in which the cochlea appears to be without internal architecture with normal (but overall elongated) external shape. (F) Drawing of an isolated malformed lateral semicircular canal.

Figure 5

Bone-CT (A) and T2 weighted-MRI (B) imaging of a case of right incomplete partition type I. The anterior and posterior parts of the labyrinth are clearly divided. The anterior part is cystic (arrows), the posterior is dysplastic, although the vestibule (asterisks) is recognizable as well as a part of the posterior semicircular canal (arrowheads).

Figure 6

Bone-CT (A) imaging of a case of left incomplete partition type II and enlarged vestibular aqueduct (black arrow). T2 weighted-MRI (B) imaging of a case of right incomplete partition type II with enlarged endolymphatic sac (white arrow). Note in both images the presence of the upper part of the cochlea that appears to be globose (asterisks). The incomplete partition type II and the enlarged vestibular aqueduct are frequently both present in the same patient.

Figure 7

Bone-CT (A) and T2 weighted-MRI (B) imaging of a case of right incomplete partition type III. The cochlea appears to be without internal architecture, with the cochlear nerve clearly visible within (white arrow). The posterior labyrinth is almost always normal, but the absent fundus of the internal auditory canal (asterisk is the position in which it should be present in normal cochleae) can cause a third-window effect causing potential vestibular symptoms.

Figure 8

Bone-CT (A) and T2 weighted-MRI (B) imaging of a case of bilateral enlarged vestibular aqueduct (white arrows) and bilateral dysplastic lateral semicircular canals (asterisks). In CT the vestibular aqueduct is enlarged (white arrows), in MRI it is possible to observe the large endolymphatic sac within (white arrowheads) and in the middle cranial fossa.