Congenital Malformations of the Outer, Middle, Inner Ear and Cochlear Nerve with Favorable Cochlear Implantation

Abstract

This case study presents the neuroradiological findings of two deaf children with CHARGE syndrome and oculo-auriculo-vertebral spectrum disease. Both patients had rare combinations of ear and auditory nerve anomalies associated with a high risk of intra- and postoperative complications during cochlear implantation (CI) and poor results. However, CI was carried out with favorable results in terms of hearing and speech development. When determining indications for CI in children with complex anomalies, it is necessary to assess the state of all ear structures in computed tomography of the temporal bones and MR (3 Tesla) images. The most critical is the state of the following structures: cochlea—modiolus—cochlear aperture—diameter of the internal auditory canal—the presence and condition of the auditory nerve. In the presence of a normal or dysplastic cochlea, a hypoplastic auditory nerve is not a contraindication for CI. In this situation, the presence of a modiolus and at least partially open cochlear aperture are prognostically favorable. In the presence of a large or small common cavity, an undivided vestibulocochlear nerve is not considered a contraindication for CI. Such a combination—a common cavity and an undivided vestibulocochlear nerve—is a prognostically quite favorable option.

1. Introduction

Congenital malformations of the inner ear structures can occur in various combinations and be combined with anomalies of the outer and middle ear, as well as aplasia/hypoplasia of the cochlear nerve. At the same time, aplasia/hypoplasia of the cochlear nerve can occur both in stenotic and normal internal auditory canal (IAC).

Regarding the anomalies of the inner ear, the greatest doubts in terms of the prospects of cochlear implantation (CI) are the absence or induration of the modiolus, stenosis/obliteration of the cochlear aperture and the dubious condition of the cochlear nerve [1].

Abnormal middle ear anatomy affects surgical landmarks and in some cases makes it difficult to identify the cochlea [2]. The absence of the auditory nerve is a contraindication to surgery, and the correct assessment of its condition in case of hypoplasia essentially determines the fate of a deaf child.

CI in cases of severe combined ear anomalies is associated with a high risk of intra and postoperative complications and poor results. To determine the indications for cochlear implantation in children with complex temporal bone malformations, it is necessary to perform high-resolution computed tomography (CT) of the temporal bones and 3 T magnetic resonance imaging (MRI) of the cochlear nerves. The results of the studies should be evaluated by an experienced radiologist to determine contraindications and assess the likelihood of intraoperative complications. The increase in the number of such patients requires clear indications for CI, as it has an economic interest.

There is an opinion that modern imaging methods cannot accurately reflect the state of the cochlear nerve or predict the benefit of CI for a child [3]. The presence of several anomalies of the temporal bone further complicates the decision to operate. Therefore, the demonstration of variants of complex combined anomalies with a positive effect of CI is useful for resolving the issue of surgery when faced with similar cases.

Particularly complex combined malformations of the temporal bone structures occur in CHARGE syndrome (CS) [4] and in diseases of the oculo-auriculo-vertebral spectrum (OAVS) [5].

2. Objective

To report the neuroradiological findings of two deaf children with CS and OAVS who underwent CI with favorable outcomes in terms of hearing and language development.

3. Materials and methods

Two children (male and female), one with CS, the other with OAVS, who, according to a comprehensive audiological examination (OAE, impedance, auditory evoked potentials and hearing aid fitting) had bilateral total deafness.

High-resolution CT was performed on a GE Revolution Discovery CT tomograph.

MRI of the brain with a targeted study of the cochlear nerves and intravenous contrast enhancement with a gadovist was performed on a GE 3 T Discovery 750 tomograph according to the technique described by Glastonbury C. M. et al. [6].

4. Results

Case 1. Young female I., born in 2017, with phenotypic signs of CS. There was a delay in physical development. She was оbserved by an ophthalmologist with diagnoses—coloboma of the optic nerve and choroid, microcornea, microphthalmos, complex astigmatism and non-permanent concomitant convergent strabismus. The child has auricular dysplasia, more on the right, audiological screening failed in both ears. A comprehensive audiological examination at the age of 4 months established a bilateral severe hearing loss. The young female was fitted with powerful hearing aids and spoke short, simple words (mom, dad). In the first 3 years of life, gradually progressive hearing loss was noted, with some fluctuation of hearing thresholds, from severe hearing loss to complete deafness. The super-power hearing aids had no effect.

CT of the temporal bones revealed a bilateral congenital anomaly of the middle and inner ear. On both sides, the anvil-malleolar complex and the long process of the incus were formed correctly. The stirrup is large, and fixation of the posterior leg to the canal of the facial nerve is noted. The oval window is reduced, compacted, and the round window is formed correctly. The vestibule is somewhat expanded. The cochlear aqueducts are formed correctly. The vestibule aqueduct is narrow. The semicircular canals are not formed. The IAC has a diameter of 4 mm. The facial nerve canal is formed typically, and the bone walls are preserved. Lateralization of the sigmoid sinus is noted.

On the right, the cochlea is dysplastically formed, and the apical turn is somewhat reduced. The modiolus and its base are considerably compacted. The aperture of the cochlea is sharply narrowed and compacted (Figure 1a–d).On the left, the cochlea is formed with incomplete separation of the curls. The number of turns has been reduced. The modiolus is not visible. The area of the cochlear aperture is completely covered by bone tissue (Figure 2a–d).

Figure 1

(a–e) Young female I., CS. Axial and coronary tomograms of the right temporal bone.

1—large stirrup, 2—well-formed round window, 3—the modiolus is significantly compacted, 4—the cochlear aperture is sharply narrowed, compacted, 5—the oval window is reduced in size, compacted, 6—the anvil-hammer complex is not changed, 7—the vestibule is somewhat expanded, the semicircular canals are absent, 8—the internal auditory canal has a normal diameter, 9—cochlear nerve, 10—facial nerve and 11—vestibular nerve.

Figure 2

(a–e) Young female I., CS. Axial and coronary tomograms of the left temporal bone.

1—large stirrup, 2—correctly formed round window, 3—incomplete separation of the cochlear turns with a decrease in their size, the modiolus is absent, 4—the cochlear aperture is closed by bone tissue, 5—the oval window is reduced in size, compacted, 6—the anvil-malleolar complex is not changed, 7—the vestibule is somewhat expanded, the semicircular canals are absent, 8—the internal auditory canal has a normal diameter, 10—facial nerve and 11—vestibular nerve.

Conclusion—CT picture of bilateral anomaly of the stapes, fenestra vestibule, aplasia of the semicircular canals, cochlear dysplasia, stenosis and partial obliteration of the cochlear aperture on the right and complete obliteration of the cochlear aperture on the left.

MRI 3 T—On the right—hypoplasia of the cochlear nerve (filiform) (Figure 1e), on the left—aplasia of the cochlear nerve (Figure 2e). The council decided to perform CI on the right ear. After the operation, she regularly works with a speech and language pathologist, understands addressed speech and speaks in phrases.

Case 2. Young male T., born in 2021. At birth, OAVS was established, a normal male karyotype. DiGeorge syndrome and velocardiofacial syndrome have been ruled out by genetic tests, and genome sequencing is underway. The child has a transverse cleft of the face, bilateral microtia, narrow external auditory canals and appendages of the auricles. A comprehensive audiological examination revealed bilateral complete deafness. Attempts of the super-power hearing aids fitting of air and bone conduction were ineffective.

CT of the temporal bones—on both sides—the mastoid process has a cellular system, developed according to age, the pneumatization of which is not disturbed. The external auditory canal has a diameter of 6 mm. The bone part of the auditory tube and the tympanic cavity are pneumatized. The facial nerve canal can be traced only in the mastoid part. The canal of the internal carotid artery is not clearly visible. The fossa of the jugular vein and the sigmoid sinus is determined.

On the right, the auditory ossicles are represented by the malleus, anvil and arch of the stirrup. The footplate of the stirrup is not formed. The medial wall of the tympanic cavity is formed abnormally. The structures of the inner ear are represented by a single large cystic cavity, a fragment of which, 3x5 mm in size, prolapses like a hernia into the tympanic cavity through a 2 mm hole in the medial wall. IAC has a diameter of 0.5 mm (Figure 3a–f).

Figure 3

(a–g) Young male T. Axial and coronary tomograms (CT and MRI) of the right temporal bone.

1—arch of the stirrup without footplate, 2—long process of the incus, 3—medial wall of the tympanic cavity, 4—anvil-malleolar complex, 5—internal auditory canal, 6—common cavity, 7—hernial-like protrusion of the lower sections of the common cavity into the tympanic cavity.

On the left, the auditory ossicles are represented by the malleus, an incus with a dysplastic long process and an arch of the stirrup. The footplate of the stirrup is not formed. The medial wall of the tympanic cavity is formed abnormally. The structures of the inner ear are represented by a single cystic cavity of small size. IAC has a diameter of 1 mm (Figure 4a–f).

Figure 4

(a–h) Young male T. Axial and coronary tomograms (CT and MRI) of the left temporal bone.

1—arch of the stirrup without footplate, 2—long process, 3—medial wall of the tympanic cavity, 4—incus-malleolar complex, 5—internal auditory canal, 6—common cavity and 7—neural structures in the internal auditory canal.

Conclusion—CT picture of a bilateral congenital anomaly of the middle and inner ear. On the right—a large common cavity prolapses like a hernia into the tympanic cavity. Severe stenosis of the IAC. Anomaly of the facial nerve canal. On the left is a small common cavity. Stenosis of the IAC. Anomaly of the facial nerve canal.

MRI of the brain and cochlear nerves. On the right—a common cavity 8х6.5 mm in size. The IAC is a narrow slit with a diameter of 0.5 mm. Neural structures are not visible (Figure 3g). On the left—a common cavity 3х2.5 mm in size. The IAC is 1.5x2.5 mm and contains cerebrospinal fluid, against which two neural structures (facial and undivided vestibulocochlear nerve) are traced, each up to 0.5 mm in diameter (Figure 4g and h).

Conclusion—MRI picture of aplasia of the vestibulocochlear nerve on the right and aplasia/hypoplasia on the left (caliber up to 0.5 mm) without signs of separation. Bilateral stenosis of the IAC. The council decided to perform cochlear implantation on the left ear. When the speech processor of the CI was first connected, a confident response to sounds was obtained, and further adjustments are being made.

5. Discussion

In the past decade, only one stenosis of the IAC, with a canal diameter of less than 1–2 mm, was considered a contraindication to CI. Currently, the indications for CT are expanding, and some children who previously belonged to absolutely unpromising children have moved into the group of potentially promising children, provided that the state of the anatomical structures of the temporal bone is correctly assessed. This was facilitated by the great technical progress of methods of radiation diagnostics. Thinner slices on CT and increased use of 3 T MRI have allowed for a finer level of evaluation of the anatomical structures of the temporal bone, especially the modiolus, cochlear aperture and cochlear nerve.

Conclusions: At present, stenosis of the IAC has ceased to be an absolute contraindication to CI. When determining the indications for CI and assessing its prospects in children with complex anomalies, it is necessary to comprehensively assess the state of all ear structures in CT and MR (preferably 3 T) images. In this case, the most critical is the state of the following structures: cochlea—modiolus—cochlear aperture—diameter of the IAC—the presence and condition of the cochlear nerve.

The absence of an image of the cochlear nerve (in the study of MRI 3 T) with complete bone obliteration of the cochlear aperture makes CI extremely unpromising.

In the presence of a normal or dysplastic cochlea, a hypoplastic cochlear nerve is not a contraindication for CI. In this situation, the presence of a modiolus and at least partially open cochlear aperture is prognostically favorable. Even in the case of hypoplasia of the cochlear nerve, the operation makes sense, and one can count on some success with this combination of anomalies.

Also, some clue pointing to the prospects of CI in severe anomalies of ear development can be the presence of certain hearing thresholds in a child before hearing falls to complete deafness.

In the presence of a large or small common cavity, an undivided vestibulocochlear nerve is not considered a contraindication for CI. Such a combination—a common cavity and an undivided vestibulocochlear nerve—is a prognostically quite favorable option.

Our results are encouraging and helpful in advising families on the likelihood of outcomes in relation to speech and auditory comprehension.

Conflict of interest

None.