Cochlear implantation under the first year of age--the outcomes. A critical systematic review and meta-analysis

To review the current knowledge on cochlear implantation in infancy, regarding auditory perception/speech production outcomes.

Meta-analysis. EBM level: II.

Literature-review from Medline and database sources. Related books were also included.

The number of cohort-studies comparing implanted infants with under 2-year-old children was five; three represented type-III and two type-II evidence. No study was supported by type I evidence. Overall, 125 implanted infants were identified. Precise follow-up period was reported in 82. Median follow-up duration ranged between 6 and 12 months; only 17 children had follow-up duration equal or longer than 2 years. Reliable outcome measures were reported for 42 infants; 15 had been assessed with open/closed-set testing, 14 with developmental rating scales, and 13 with prelexical speech discrimination tools. Ten implanted infants assessed with open/closed-set measures had been compared with under 2-year-old implanted children; 4 had shown better performance, despite the accelerated rate of improvement after the first postoperative year.

Neuroplasticity/neurolinguistic issues have led cochlear implant centers to implant deaf children in infancy; however, widespread policies regarding the aforementioned issue are still not justified. Evidence of these children's outperformance regarding auditory perception/speech production outcomes is limited. Wide-range comparisons between infant implantees and under 2-year-old implanted children are lacking. Longer-term follow-up outcomes should be also made available. There is a need to develop and validate robust measures of monitoring implanted infants. Potential factors of suboptimal outcomes (e.g. misdiagnosis, additional disorders, device tuning, parental expectations) should also be weighted, when considering cochlear implantation in infancy.