Radiological diagnosis of the inner ear malformations in children with sensorineural hearing loss

Abstract

Malformations in either the inner ear, vestibulocochlear nerve (VIIIth) or auditory cortex of the brain can lead to congenital sensorineural hearing loss (SNHL). In most cases the underlying disorders involve the membranous labyrinth at a microscopic level and therefore radiological examinations are entirely normal. In a significant proportion however (up to 20%), there are abnormalities visualized in the inner ear and/or the VIIIth nerve; the type of abnormality is relevant for the surgical planning of a cochlear implant. Imaging and the accurate radiological identification of the affected inner ear structures therefore plays an integral role in the clinical evaluation of sensorineural hearing loss. In this pictorial review, we describe the main malformations of the inner ear in view of recent classifications and briefly explore the surgical implications.

Figure 1.

Axial high-resolution 3D T ₂WI of the labyrinth showing a normal cochlea with well-formed interscalar septum dividing the different cochlear turns (arrows in A) and the lamina spiralis dividing scala vestibuli and scala tympani (thin arrow in B). The modiolus is visible in A as a hypointense triangular area. The VIIIth nerve and its cochlear and vestibular divisions are noted (arrowhead in A). The VIIIth (white thick arrow) and VIIth (thick black arrow) nerves in the cisternal portion are seen in B (slightly cranial to A). 3D, three-dimensional; T ₂ WI, T ₂ weighted imaging.

Figure 2.

Parasagittal MRI reformat perpendicular to the IAC showing VIIth nerve (red arrow), cochlear nerve (blue arrow) and vestibular nerves (green arrow) with the inferior and superior vestibular branches still unified. IAC, internal auditory canal.

Figure 3.

Chart for evaluation of SNHL in children. SNHL, sensorineural hearing loss.

Figure 4.

Axial CT showing complete labyrinthine aplasia in patient with LAMM syndrome (Congenital deafness with labyrinthine aplasia, microtia, and microdontia), no labyrinthine is seen in a small and dense otic capsule (arrow). Figure 4B Rudimentary otocyst (white arrow) with narrowed IAC (black arrowhead). IAC, internal auditory canal.

Figure 5.

Cochlear aplasia on CT (left) and MRI (right) on axial planes. Note dysmorphic vestibule (arrows) and absent cochlear promontory (arrowhead) in keeping with cochlear aplasia with a dilated vestibule.

Figure 6.

Showing typical common cavity without internal structure (red arrow). It takes its shape from the confluence of the outline of the cochlea and vestibule and is contiguous with the IAC (green arrow). Note that the cochlear promontory is not present given the absence of the basal turn of cochlea. IAC, internal auditory canal.

Figure 7.

Type 1 incomplete partition appearances on MRI (left) and CT (right), the cochlea has normal dimension and no internal partitioning (arrowheads), the vestibule and semi-circular canals are dysmorphic (arrows).

Figure 8.

MRI appearances of incomplete partition Type 2, note cystic-like appearance of the upper cochlear turn with flattening of the interscalar septum laterally (red arrow), dilated and dysmorphic vestibule (green arrow) and enlarged endolymphatic sac (blue arrow).

Figure 9.

Typical CT (up) and MRI (down) appearances of incomplete partition Type 3. Note the enlarged internal auditory meatus (*), the presence of cochlear nerves (dotted arrow) and the preserved interscalar septi accounting for the typical shape of the cochlea in these patients (arrows).

Figure 10.

CT appearances of cochlear hypoplasia Type 1 (arrows in A) and Type 2 (arrow in B). Two different MRI appearances of cochlear hypoplasia Type 3 (C) and 4 (D) with relatively preserved internal structure and normal sized basal turn noted only in Type 4 (arrow in D).

Figure 11.

Dysplastic lateral semi-circular canal (red arrow), showing its typically short and wide morphology. The cochlea is abnormal with a hypoplastic interscalar septum between the middle and apical turn (green arrow).