What are the causes of unilateral sensorineural hearing loss in children?

Causes of Unilateral Sensorineural Hearing Loss in Children

Unilateral sensorineural hearing loss in children is most commonly caused by congenital cytomegalovirus (cCMV) infection, inner ear malformations (particularly cochlear nerve deficiency), and genetic syndromes, though genetic testing yields only 1-5% diagnostic rate for unilateral cases compared to bilateral hearing loss. 1

Primary Etiologic Categories

Structural/Anatomic Abnormalities (Most Common)

• Cochlear nerve deficiency/aplasia represents the predominant cause of unilateral neural hearing loss, accounting for approximately 73% of cases with the neural phenotype (present otoacoustic emissions despite hearing loss) 2
• Inner ear malformations including Mondini deformity with enlarged vestibular aqueduct are associated with progressive hearing loss 1
• Structural anomalies account for approximately 19% of congenital unilateral cases 3
• Temporal bone anomalies and craniofacial syndromes (Crouzon disease, Klippel-Feil syndrome, Goldenhar syndrome) are associated with unilateral presentations 1

Congenital Infections

• Congenital CMV is a leading nongenetic cause, representing approximately 13% of congenital unilateral sensorineural hearing loss 3
• cCMV may present with asymptomatic infection, making targeted screening after failed newborn hearing screening critical 1
• Congenital rubella, syphilis, toxoplasmosis, and herpes are additional prenatal infections, though rubella has become rare in developed countries due to vaccination 1

Genetic Etiologies

• Genetic variants are identified in approximately 20-21% of childhood unilateral cases, with most diagnoses representing syndromic etiologies 1, 4
• GJB2 (connexin-26) variants account for the majority of genetic cases (5 of 8 in one series), typically presenting with mild-to-moderate hearing loss in various audiogram configurations 4
• PAX3 and EDNRB variants (associated with Waardenburg syndrome) present with profound hearing loss in flat audiogram configurations 4
• The diagnostic yield of next-generation sequencing gene panel testing for unilateral hearing loss is only 1-5%, substantially lower than bilateral cases 1

Perinatal and Postnatal Causes

• Prematurity, asphyxia, and complicated NICU courses (>5 days stay, ECMO, assisted ventilation, hyperbilirubinemia requiring exchange transfusion) 5
• Culture-positive bacterial and viral meningitis (Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae), though substantially reduced due to vaccination programs 1, 5
• Ototoxic medication exposure, particularly aminoglycosides (with potential genetic predisposition via MT-RNR1 variants) 1, 5

Traumatic Causes

• Significant head trauma, basal skull/temporal bone fractures, and barotrauma 5

Tumors

• Mass lesions must be considered in children with unilateral sensorineural hearing loss, particularly those with neural patterns (present OAEs) 2
• MRI identified previously unsuspected tumors in 2 of 10 patients evaluated for unilateral neural hearing loss 2

Critical Diagnostic Considerations

Imaging Requirements

• MRI is superior to CT for evaluating unilateral sensorineural hearing loss, as it can identify cochlear nerve aplasia and mass lesions that elude CT detection 2
• Temporal bone CT may identify cochlear abnormalities like Mondini deformity but misses neural pathology 1

Genetic Testing Approach

• Genetic testing should be considered for unilateral hearing loss despite low yield (1-5%), particularly because syndromes can present with subtle findings 1
• Testing is most valuable when syndromic features are present, as 26% of congenital unilateral cases have associated syndromic features 3
• Extended gene panels targeting 30+ deafness genes are appropriate initial testing 4

Progression Risk

• Unilateral hearing loss may progress to bilateral involvement, making longitudinal monitoring essential 1
• Enlarged vestibular aqueduct and certain genetic conditions carry higher progression risk 1

Common Pitfalls

• Approximately 24% of congenital unilateral cases remain idiopathic even after comprehensive etiological work-up 3
• Family history is unreliable for screening, as over 90% of children with autosomal recessive profound hearing loss are born to hearing parents 5
• Unilateral cases may be missed until preschool age without universal newborn hearing screening, as they typically have normal language development 6
• Failing to perform MRI in neural hearing loss patterns (present OAEs with hearing loss) risks missing cochlear nerve aplasia or tumors 2