Congenital Inner Ear Malformations - Risk Factors, Diagnosis, and Management

Introduction

Beginning in the third week of intrauterine life, the embryologic development of the inner ear takes place in a predetermined order. Several anatomical abnormalities may appear depending on when the injury occurs in utero. Only a small percentage of patients (20 to 30 %) on imaging may exhibit radiologic abnormalities. This has been linked to changes happening at the microscopic or cellular levels that are too small for existing imaging tools to resolve. Congenital deaf-mutism commonly manifests in these kids throughout their early years of life. A thorough physical examination is necessary since these kids frequently have systemic problems in addition to inner ear deformities.

Hearing aids, cochlear implants, and auditory brainstem implants (ABI) are the three options accessible for these people for hearing rehabilitation. Cochlear implantation has been demonstrated to be both clinically and financially beneficial in children with severe to profound bilateral sensorineural hearing loss. High-resolution computed tomography (HRCT), temporal bone, and magnetic resonance imaging (MRI) have become indispensable in the imaging evaluation and characterization of inner ear defects due to the extensive use of cochlear implantation. While MRI effectively illustrates the membrane labyrinth, vestibulocochlear nerve, and brain disease, HRCT depicts the bone labyrinth, skeletal features, and variable anatomy. These findings can influence the choice between ABI and cochlear implants. The decision between these two imaging modalities for preoperative imaging differs between institutions, with some choosing to use both of these modalities in a complementary way. In contrast, others rely predominantly on either CT or MR imaging. Imaging results impact the surgical method and the choice of the electrode when a cochlear implant is intended.

What Is the Epidemiology of Congenital Inner Ear Malformations?

One in 10,000 or 20,000 people have ear abnormalities. A sensorineural hearing impairment affects one out of every 1,000 kids, with an average diagnosis of 4.9 years. In addition, it has been shown that 9.52 % of babies with risk factors had a hearing impairment.

What Are the Risk Factors of Congenital Inner Ear Malformations?

The following are the associated risk factors of congenital inner ear malformations:

• Ototoxic consumption (medications that can damage the ear).

• Male sex.

• More than five days in the intensive care unit (ICU).

• Less than 34 weeks along in the pregnancy.

• Exchange transfusion.

• TORCH Syndrome (toxoplasmosis, others (syphilis, hepatitis B), rubella, cytomegalovirus, herpes simplex).

• Hyperbilirubinemia (excessive presence of bilirubin in baby's blood).

• Respiratory distress from meconium aspiration.

• Craniofacial changes.

• Mechanical ventilation for longer than five days.

How Are Congenital Inner Ear Malformations Diagnosed?

Pathologies in the inner ear are investigated using magnetic resonance imaging (MRI) and computed tomography (CT). While MRI enables better examination of soft tissues, such as the membranous labyrinth, and the representation of cranial pairs, CT is the imaging technique of choice for evaluating the skeletal structures of the ear. As previously stated, 7 to 20 % of patients with congenital hearing loss have detectable radiological changes.

What Is the Classification of Congenital Malformations of the Inner Ear?

The following is the classification:

1. Cochlear Malformations:

• Michel's deformity is the total absence of all vestibular and cochlear structures.

• Cochlear aplasia (the cochlea is completely absent).

• Common cavity deformity (cochlea and vestibule replaced with a cystic cavity).

• Cochlear hypoplasia (the cochlea and vestibule are less developed than usual).

• Incomplete Partition Type 1 (IP-I), wherein the cochlea is accompanied by a sizable cystic vestibule but lacks a modiolus.

• Mondini malformation, also known as incomplete partition type II (IP-II), is characterized by a 1.5-turn cochlea with a cystic apex, a dilated vestibule, and an expanded vestibular aqueduct.

2. Vestibular Malformations:

• Semicircular Canal Malformations: Hypoplastic, missing, or dilated semicircular canals are all examples of semicircular canals.

• Malformations of the Internal Auditory Canal: There is no internal auditory canal, the internal auditory canal is small, or the internal auditory canal is dilated.

3. Cochlear Aplasia and Hypoplasia: Five percent of cochlear abnormalities are cochlear aplasias. After the third week of pregnancy, embryonic development ceases, typically due to an unknown cause. Cochlear hypoplasia, which accounts for 12 % of cochlear abnormalities, results from a change in the cochlear canal's development during the sixth week of pregnancy. Clinically, patients exhibit sensorineural hearing loss that is either unilateral or bilateral from birth.

Diagnostic imaging is used to identify both pathologies. In cochlear aplasia, the semicircular canals are frequently malformed, globular, or dilated, and the cochlear nerve and its conduit are absent; in contrast, in cochlear hypoplasia, a small cochlea with a single primitive spiral is seen, and the vestibule and semicircular canals may be normal.

4. Incomplete Partition Type 1: With a cystic cochlea and a dilated vestibule, it makes up 20 % of cochlear abnormalities. It starts during the fifth week of pregnancy and impacts how the internal cochlear structure develops. In contrast to the more advanced degree, when the cochlea, vestibule, and horizontal semicircular duct are globularly expanded and form an outline, the moderate degree only exhibits the malformation at the level of the cochlea, with normal semicircular ducts and absent modiolus. By using a CT scan, radiological findings are found.

The second most common reason for congenital deafness is Mondini's aplasia. About 19 % of cochlear abnormalities are caused by it and around 30 % of all congenital inner ear abnormalities. A cystic cochlear apex, limited vestibule dilatation, and a lengthy vestibule aqueduct make up the trinity that defines it. The cochlear development is interrupted at one and a half turns, resulting in this deformity, which is linked to complete deafness and vestibular malformations. A developmental arrest causes this anomaly during the seventh week or a developmental arrest of the ear between days 58 and 70 of gestation. Some Mondini malformation individuals have mild sensorineural deafness, while others have extensive deafness, according to the diagnosis.

5. Vestibular and Semicircular Canal Malformations: The sixth week of gestation marks the start of the semicircular canals' embryological development, which lasts until week 22. Depending on the association with cochlear abnormalities, the clinical presentation based on vestibular change may result in varying degrees of hearing loss. CT is the preferred diagnostic technique in this situation. They can also be found using high-resolution magnetic resonance imaging and multiplanar reconstructions.

How to Manage Congenital Inner Ear Malformations?

The management of these malformations depends on the specific type and severity of the condition. It is essential to consult with a medical professional, preferably an otolaryngologist or an otologist, who specializes in ear disorders. They can provide a thorough evaluation and develop an appropriate management plan tailored to the individual's needs. However, here are some general aspects of managing congenital inner ear malformations:

• Diagnosis and Evaluation: Accurate diagnosis and a comprehensive evaluation of the malformation are crucial. This may involve a combination of medical history assessment, physical examination, audiological tests, imaging studies (such as CT scan or MRI), and genetic testing if necessary. The results will help determine the type and severity of the malformation.

• Hearing Assessment: Hearing loss is a common issue associated with congenital inner ear malformations. A hearing evaluation, including pure-tone audiometry, speech audiometry, and otoacoustic emissions (OAE) testing, can help determine the degree and type of hearing loss. This information is important for treatment planning.

• Communication Options: Depending on the severity of the hearing loss, communication options can vary. These may include hearing aids, cochlear implants, or other assistive listening devices. A specialist will guide patients on the most suitable communication option based on the individual's hearing ability, overall health, and personal preferences.

• Educational Support: If the congenital inner ear malformation affects a child's hearing and communication abilities, educational support is vital. Early intervention programs, speech therapy, and special education services can facilitate language development and academic progress.

Conclusion

A significant contributing factor to sensorineural hearing loss in youngsters is congenital inner ear deformity. It includes modini deformity, cochlear hypoplasia, cystic cochleovestibular anomaly, labyrinthine aplasia, and cochlear aplasia. The management of these malformations depends on the type and severity of the disorder. An ear specialist can recommend an appropriate management plan depending on the condition of the patient.