A 6-month-old boy born at 28 weeks gestation is referred to audiology after failing newborn screening. Audiological testing shows pure-tone thresholds of 85 dB HL bilaterally, but otoacoustic emissions (OAEs) are robustly present. Auditory brainstem response (ABR) is absent bilaterally. The infant's parents report he does not turn to sound or babble, despite appearing to respond to vibration. The pattern marked **B** in the diagram best describes this infant's audiological profile. Which of the following is the most appropriate next diagnostic step to guide management?
A. Genetic testing for GJB2 mutations to identify connexin-26 deficiency
B. MRI of the internal auditory canals and cochlear nerves using high-resolution FIESTA/CISS sequences to assess nerve anatomy
C. Tympanometry and acoustic reflex testing to rule out conductive pathology
D. Repeat ABR testing at higher stimulus intensities to confirm absent response
Explanation
Why MRI of the internal auditory canals and cochlear nerves is correct
The diagnostic tetrad of ANSD (present OAEs + absent ABR + absent reflexes + poor speech perception) is clearly demonstrated in this case. The critical next step after confirming ANSD is structural imaging with high-resolution FIESTA/CISS MRI sequences to evaluate cochlear nerve anatomy (hypoplasia vs aplasia vs normal). This finding directly determines candidacy and expected outcomes for cochlear implantation — the treatment of choice for severe-profound ANSD. If the nerve is intact, cochlear implant outcomes are excellent; if the nerve is aplastic, implantation will fail. The perinatal history (prematurity, presumed NICU stay) raises concern for hyperbilirubinemia-related kernicterus or hypoxic-ischemic injury, both known causes of ANSD. MRI is essential before proceeding to implant evaluation (Bayes-Joint Committee Infant Hearing 2019; AAA ANSD guidelines).
Why each distractor is wrong
Repeat ABR at higher intensities: ABR is already absent at standard intensities in ANSD. Increasing stimulus intensity will not elicit a response because the problem is neural transmission, not cochlear sensitivity. This is not a diagnostic step and wastes time.
Genetic testing for GJB2 mutations: GJB2 (connexin-26) causes non-syndromic conductive or sensorineural hearing loss with NORMAL ABR and absent OAEs — the opposite of this patient's profile. GJB2 testing is not indicated in ANSD. Genetic panels targeting OTOF, PJVK, OPA1, and MPZ would be appropriate after imaging, but not GJB2.
Tympanometry and acoustic reflex testing: While absent middle ear muscle reflexes are part of the ANSD tetrad, tympanometry is normal in ANSD (the problem is neural, not mechanical). This test does not guide management and delays the critical imaging needed to assess nerve integrity.
High-YieldNEET PG
ANSD = absent ABR + present OAE; next step = MRI to assess cochlear nerve anatomy (determines CI candidacy); OTOF mutations are most common genetic cause and temperature-sensitive.
