The Laryngoscope V C 2011 The American Laryngological, Rhinological and Otological Society, Inc. Contemporary Review What Is the Effect of Time Between Sequential Cochlear Implantations on Hearing in Adults and Children? A Systematic Review of the Literature Yvette E. Smulders, MD; Albert B. Rinia, MD; Maroeska M. Rovers, PhD; Gijsbert A. van Zanten, PhD; Wilko Grolman, MD, PhD Objectives/Hypothesis: Bilateral cochlear implantation is a safe and effective intervention for severe sensorineural hearing loss and is believed to be more effective than unilateral implantation. This review article investigates the effect of time between sequential cochlear implantations on hearing results in both adults and children. Study Design: Systematic review of cohort studies. Methods: We searched PubMed, Embase, and CINAHL from inception to August 16, 2010, using the terms hearing loss, cochlear implant, delay, and their synonyms. Results: Eleven studies evaluating the effect of time between sequential cochlear implantations on hearing performance were included. Although the quality of studies was poor because of a significant risk of bias, all studies reported that auditory performance is better in a bilateral listening situation than with either one cochlear implant activated unilaterally. Five stud- ies discussed postlingually deafened adults. In four, bilateral hearing was not affected by the amount of time between implan- tations. One study did report a negative effect of delay on speech intelligibility in silence. Seven studies discussed prelingually deafened children. None reported a negative effect of interimplantation delay on sound localization performance. One study reported poorer results after extended intervals on speech intelligibility in silence and two in noise. Conclusions: Current evidence suggests that a second implant can be beneficial even after a substantial interval between sequential implantations. The quality of the evidence is, however, rather poor; to confirm this postulation, high-quality trials assessing the effectiveness of a second cochlear implant after a time delay should be initiated. Key Words: Sequential, cochlear implantation, delay, adults, children. Level of Evidence: 2A Laryngoscope, 121:1942–1949, 2011 INTRODUCTION Bilateral cochlear implantation (BICI) is growing in popularity for the treatment of severely deafened adults and children. There are three motivations for bilateral implantation: 1) to ensure that best ear is stimulated, 2) to provide a backup in the event of device failure, and 3) to create the potential for binaural hearing and benefit from its perceptive effects: ‘‘head shadow effect,’’ ‘‘sum- mation effect,’’ and ‘‘squelch effect.’’ 1–4 Previous studies that compared unilateral with bilat- eral cochlear implantation showed that auditory outcomes are better for bilateral than unilateral listening situations. The addition of a second cochlear implant (CI) leads to better performance in difficult-listening situations such as selective listening to a sound of interest in noisy conditions and localization of sounds. 1,2,5 More- over, binaural hearing is believed to play a key role in the development of language and speech in children. 1–3 In general, simultaneous BICI is believed to be preferential over sequential implantation. Simultaneous implantation prevents the occurrence of timing differen- ces of brainstem activity that may develop in the case of prolonged unilateral CI usage and may compromise the development of binaural hearing in infants. 4,6 Although the interest in BICI is growing among uni- laterally implanted patients and their caregivers, new questions arise. Is BICI beneficial, even if there is a delay between the placement of the first and second CI? How long after unilateral cochlear implantation can a second CI contribute to improved hearing? From the Department of Otolaryngology (Y.E.S., A.B.R., M.M.R., G.A.V .Z., W.G.), Rudolf Magnus Institute of Neuroscience (Y .E.S., W.G.), and Julius Center for Health Sciences and Primary Care (M.M.R.), University Medical Center Utrecht, Utrecht, The Netherlands; and Department of Otolaryngology, Academic Medical Center Amsterdam ( A. B. R.), Amsterdam, The Netherlands. Editor’s Note: This Manuscript was accepted for publication May 10, 2011. Send correspondence to Yvette E. Smulders, MD, Department of Oto- laryngology, University Medical Center Utrecht, G02.531, PO Box 85500, 3508 GA Utrecht, The Netherlands. E-mail: Y.E.Smulders@umcutrecht.nl/ ENT-research@umcutrecht.nl DOI: 10.1002/lary.21922 Laryngoscope 121: September 2011 Smulders et al.: Second Cochlear Implantation After Time Delay 1942