High-resolution 3 T magnetic resonance findings in cochlear hypoplasias and incomplete partition anomalies: a pictorial essay

Abstract

Inner ear malformations are recognized by imaging in about 20% of children with congenital sensorineural hearing loss. Normal development of the inner ear structures can be affected by many factors, including genetic anomalies as well as environmental destructive causes (ischemic, infectious, radiation and more). Recently, histopathological studies have provided new insights on the anatomy and pathogenesis of inner ear malformations, especially regarding incomplete partition and cochlear hypoplasia (CH), for which different subtypes have been identified. Factors known for interfering with normal inner ear development are numerous and sometimes act simultaneously, making the understanding of their pathophysiology more challenging. Vascular supply from the internal auditory canal seems to be critical for normal development of internal structures of the labyrinth while a premature arrest in the spatial development of the cochlea due to genetic or toxic factors may result in short cochlea (i.e.: CH). The aim of this essay is to show 3 T MRI appearances of the different subtypes of CH and incomplete partition introduced in the new classification (findings summary in Table 1).

Figure 1.

High-resolution axial T₂ WI 3D of a normal cochlea. Note the ability of MRI to show not only cochlear nerve (black arrowhead), but also osseous structures such as interscalar septum (short white arrow) and modiolus (long white arrow) with associated lamina spiralis. 3D, three-dimensional; T₂ WI, T₂ weighted imaging.

Figure 2.

Cochlear hypoplasia Type 1 (CH1) in a 7-month-old male with bilateral profound hearing loss. High-resolution axial T₂ WI 3D (a) and CT (b) showing a small cochlear bud with less than one turn and no internal structure compatible with CH1 (arrows); deformed vestibule and SCCs are also present. Axial T₂ CISS at the level of the IAM demonstrates presence of both VIII and VII cranial nerves (dotted arrow and short arrow respectively in c). Labyrinthine malformations were symmetrical on both sides in this patient. 3D, three-dimensional; CISS, constructive interference in steady state; IAM, internal acoustic meatus; SCC, semi-circularcanal; T₂ WI, T₂ weighted imaging.

Figure 3.

Cochlear hypoplasia Type 2 (CH2) in a 3-month-old male with Pierre-Robin sequence and bilateral profound hearing loss. High-resolution axial T₂ WI 3D shows a small cochlea with underdeveloped modiolus (arrow) and lamina spiralis (dotted arrow). The VII/VIII nerves are present on both sides (visible only on the left in the image). Coexistence of incomplete internal cochlear structure and small cochlear dimension is in keeping with CH2. 3D, three-dimensional; T₂ WI, T₂ weighted imaging.

Figure 4.

Cochlear hypoplasia Type 3 (CH3) in a 4-year-old female with bilateral profound hearing loss. High-resolution axial T₂ WI 3D shows a small cochlear with presence of fairly complete interscalar septum (arrow in a) and lamina spiralis (arrows in b, c). Only the VII nerve was clearly visualized within the IAM (dotted arrow in c). Vestibule and SCCs are hypodeveloped. 3D, three-dimensional; IAM, internal acoustic meatus; SCC, semi-circularcanal;T₂ WI, T₂ weighted imaging.

Figure 5.

MRI of the inner ears in a 10-year-old female with chronic kidney disease, dysmorphic features, bilateral hearing loss and mosaic trisomy of chromosome 22. Bilateral CH4 is demonstrated with normal-sized basal turn and very hypoplastic upper turn. Normal lamina spiralis is noted as a hypointense line within the basal turn (arrows).

Figure 6.

Different types of IP with CT (top row) and MRI (low row) correlation. High-resolution CT and high-resolution axial T₂ WI 3D in patients with IP-1 (a/a’), IP 2 (b/b’) and IP-3 (c/c’) showing similar diagnostic value of CT and MRI in identifying the type of malformation with an added value of MRI in characterising the internal cochlear structures (i.e.: modiolus and lamina spiralis) and visualisation of VIII and VII nerves. (a) Typical cystic cochleovestibular malformation of IP-1 with absence of internal structure of the cochlea and dilatation of vestibule and SCCs. The cochlear nerve was present but hypoplastic (not shown). (b) Mondini triad: dilated apical turn of the cochlea (arrow in b’) without internal structure (IP-2) but with normal basal turn, slightly dilated vestibule and markedly dilated vestibular aqueduct (dotted arrow in b’). (c) IP-3 (X-linked deafness): typical appearances of the cochlea with presence of interscalar septum (dotted arrows in c’) but absence of internal structures. Slightly dilated and malformed SCCs and vestibule are also present. 3D, three-dimensional; IP, incomplete partition; SCC, semi-circularcanal;T₂ WI, T₂weighted imaging.

Figure 7.

IP-3, same patient as in Figure 6c. Axial T₂ WI 3D showing bilateral and symmetrical IP-3 malformation: note the large IAMs, the presence of VIII nerves with cochlear and vestibular divisions and the absence of internal structure, wide cochlear aperture and normal interscalar septum (white arrows). Such findings are encountered in X-linked deafness due to POU3F4 gene mutation. 3D, three-dimensional; IAM, internal acoustic meatus; IP, incomplete partition; T₂ WI, T₂ weighted imaging.

Figure 8.

3D T₂ WI in a 2-year-old male with BOR syndrome. There is hypoplastic cochlea (dotted arrow in A) with small and dysmorphic apical portion and deficient internal structure (fitting the description of CH Type 2). Lamina spiralis is visible in the basal turn (short arrow in a). VIII nerve and cochlear division are present (long white arrow in a and black arrow in b, respectively). Lateral SCC is small (white arrow in b) and the posterior SCC is absent (i.e.: persistent anlage; arrowhead in b). 3D, three-dimensional; SCC, semi-circular canal; T₂ WI, T₂ weighted imaging.

Figure 9.

3D T₂ WI in an 1-year-old female with CHARGE syndrome. Right labyrinth (a) shows a small cochlea with markedly deficient internal structure in keeping with CH Type 2; slice at the level of the IAM on the right demonstrates very hypoplastic cochlear and vestibular nerves (arrows in b). On the left side (c) there is a small cochlear bud (CH Type 1, arrowhead), the IAM is very small and the nerves are not visualized (arrow). On both sides the vestibule is hypoplastic and dysmorphic and the SCCs are not present. (d) Axial CT of the right otic capsule demonstrating CT appearance of the right hypoplastic cochlea. 3D, three-dimensional; IAM, internal acoustic meatus; T₂ WI, T₂ weighted imaging.

Figure 10.

3D T₂ WI in a 2-year-old male with SOX 10 mutation (a, b) shows globally small cochlea with relatively preserved internal structure (CH Type 3). The lateral SCC is small and dysplastic (arrow in a) and posterior SCC is not present (i.e.: persistent anlage, dotted arrow in a). Superior SCC was also slightly small and there were hypoplastic ophthalmic nerves (not shown). The corresponding CT appearances are shown in c and d. Difference between CH3 and 4 is that in the Type 3 the basal turn is also smaller while preserved in Type 4. Inner ear malformations in this patient were symmetrical on both sides. 3D, three-dimensional; SCC, semi-circular canal; T₂ WI, T₂ weighted imaging.