CLINICAL PRESENTATIONS: HEARING LOSS
There are various classification techniques for hearing loss in children. Congenital (prelingual) hearing loss occurs before the child learns to speak. The prevalence of congenital hearing loss is 1 to 3 per 1,000 livebirths. Approximately 0.1% of children in the United States are born with profound deafness. The prevalence of late-onset (postlingual) hearing loss is about half of that of the prelingual form. About half of pediatric hearing loss is due to genetic factors, one-quarter of patients have acquired lesions, and one-quarter have idiopathic hearing loss. Seventy percent to 80% of instances of genetic deafness are nonsyndromic, that is, no associated anomalies in other parts of the body. Most patients with nonsyndromic deafness have abnormalities of the inner ear, that is, sensorineural deafness. Conductive hearing loss is due to abnormalities of the middle ear. If both sites are involved, the hearing loss is mixed.1–3
The causes of congenital hearing loss are extensive. Congenital infections are responsible for many cases. Cytomegalovirus is a common congenital infection that can cause sensorineural hearing loss. Although there are multiple potential clinical manifestations of cytomegalovirus infection, hearing loss is the only finding in some affected infants. Hearing loss can also occur with congenital toxoplasmosis (15%), congenital rubella (50%), transplacental herpes simplex type 1 infection (50%), herpes simplex type 2 infection (uncommon), and congenital syphilis. Various maternal medications can cause congenital hearing loss, including aminoglycosides and chloroquine.
Postnatal infections can also cause hearing loss. Streptococcus pneumoniae meningitis carries a 15% to 20% risk for hearing loss, which is bilateral in more than half of patients. Other forms of bacterial meningitis can also lead to hearing loss. The most important viral agents associated with acquired hearing loss in infants are mumps and measles.
Mutations in GJB2, the gene that encodes connexin 26 (Cx26), are responsible for 25% to 50% of cases of autosomal recessive nonsyndromic hearing loss, with variations in prevalence by geographic population groups. Children with defective connexin 26 have prelingual hearing loss that is usually severe. Diagnostic imaging studies of the ear show no definable anatomic abnormalities. Mutations in SCL26A4 cause Pendred syndrome, which includes hearing loss; this may account for up to 10% of cases of syndromic hearing loss. There are hundreds of other causes of syndromic hearing loss, including osteogenesis imperfecta, Usher syndrome, Treacher Collins syndrome, Goldenhar syndrome, Turner syndrome, trisomy 21, otopalatodigital syndrome, branchio-oto-renal (BOR) syndrome, Kabuki syndrome, Opitz-Frias syndrome, Möbius syndrome, Duane syndrome, Alport syndrome, Refsum disease, Jervell and Lange-Nielsen syndrome, CHARGE association, Norrie syndrome, Cockayne syndrome, mucopolysaccharidosis, DiGeorge syndrome, achondroplasia, Wildervanck syndrome, Marfan syndrome, Apert syndrome, and Waardenburg syndrome.
High-resolution CT of the temporal bones is the imaging modality of choice for the evaluation of most pediatric patients with hearing loss. The most common finding is an enlarged vestibular aqueduct. Cochlear dysplasia is also a common CT finding in children with hearing loss. ...