Auditory Brainstem Implant (ABI) in Children With No Cochleae or Auditory Nerves

Inclusion Criteria: Group 1: Prelinguistic hearing loss (birth-5 years; age at implantation of ABI 18 months-5 years) • Pre-linguistic hearing loss (birth-5 yrs.; age at ABI 18 months-5yrs) with both: * MRI +/- CT evidence of one of the following: * Cochlear nerve deficiency * Cochlear aplasia or severe hypoplasia * Severe inner ear malformation * Post-meningitis ossification * When a cochlea is present or patent, lack of significant benefit from CI despite consistent use (\>6 mo.) * No or limited speech perception ability (limited to pattern perception on closed set testing materials using the CI) * Lack of progress in auditory skills development Group 2: Post-linguistic hearing loss (\<21 yrs. of age) * Post-linguistic hearing loss (\<21 yrs. of age) with: * Loss or lack of benefit from appropriate CI without the possibility for revision or contralateral implantation. Examples might include: * Post-meningitis ossification * Bilateral temporal bone fractures with cochlear nerve avulsion * Failed revision CI without benefit * Previously developed open set speech perception and auditory-oral language skills * No medical contraindications * Willing to receive the appropriate meningitis vaccinations * No or limited cognitive/developmental delays. * Strong family support * Reasonable expectations from parents/guardians including a thorough understanding: * of potential benefits and limitations of ABI * of parental role in rehabilitation * that the child may not develop spoken language as a primary communication mode or even sufficient spoken language to make significant academic progress in an aural/oral environment * Involvement in a rehabilitation program that emphasizes development of auditory skills with or without the use of supplementary visual communication. * Able to comply with study requirements including travel to investigation sites. * Informed consent for the procedure from the child's parents/legal guardian. Exclusion Criteria: For both Groups 1 and 2: * Pre- or post-linguistic child currently making significant progress with CI Even for the very young children (18 months of age with 6 months of use), nearly all children with a good auditory signal from their CI will show evidence of improvement in these metrics over time. * MRI evidence of one of the following: * normal cochlea and cochlear nerves or NF2 * brainstem or cortical anomaly that makes implantation unfeasible * Clear surgical reason for poor CI performance that can be remediated with revision CI or contralateral surgery rather than ABI. * Intractable seizures or progressive, deteriorating neurological disorder * Patients with evidence of Chiari malformation, hydrocephalus, spina bifid a * Patients with any foreseeable need for a future MRI scan * Unable to participate in behavioral testing and mapping with their CI. If this appears to be an age effect, ABI will be delayed until we can be assured that the child will be able to participate, as reliable objective measures of mapping are currently not available for mapping these devices. * Unable to tolerate general anesthesia (cardiac, pulmonary, bleeding diathesis, etc.). * Need for brainstem irradiation * Unrealistic expectations on the part of the subject/family regarding the possible benefits, risks and limitations inherent to the procedure and ABI device. * Unwilling to sign the informed consent. * Unwilling to make necessary follow-up appointments.