Effects of CI Electrode Insertion on Tinnitus
Thomas J. Balkany, MD
Over the past three decades, several papers have demonstrated positive as well as negative effects of cochlear implantation (CI) on tinnitus (1-6).
Theoretical mechanisms of CI effects on tinnitus include electrical stimulation and electrode insertion trauma (EIT). Electrical effects may reduce tinnitus by masking (creating an auditory percept that makes tinnitus inaudible), electrical suppression (directly altering the generation or neural transmission of the tinnitus signal) or by other mechanisms. EIT may cause increasing tinnitus due to neural or metabolic organelle damage that may cause abnormal signal generation. The following discussion addresses a series of patients in whom traumatic, scala transgressing insertion exacerbated tinnitus in comparison to another cohort in whom non-scala transgressing electrodes did not.
·Pre-operative tinnitus in CI candidates has been estimated at 65 – 100%. (1, 2)
·The rate of tinnitus improvement following CI ranges from 50 – 90%. (4,5)
·Tinnitus may be generated or made worse by CI in 0 – 28% of recipients. (5, 6)
In an important paper by Ingo Todt and colleagues at Unfallkrankenhaus (UFK) in Berlin (7), post-op flat panel CT was used to determine whether or not CI electrodes ruptured inter-scalar partitions and traversed between S. tympani and S. vestibuli. Tinnitus was analyzed by standard metrics: a validated analog loudness scale and a questionnaire. Below is a summary of one of the significant outcomes. In short:
Tinnitus Worse after CI
Electrode traversed scala (n = 19): 16%
Electrode did not traverse (n = 36): 0
Good surgical technique may reduce post-CI tinnitus. In this study, only when electrodes penetrated from one scala to another (equivalent to Eshraghi-Balkany Grade IV/IV trauma (8)), was tinnitus generated or made worse.
Surgical techniques that prevent or reduce inter-scalar transgression may be expected to reduce post-implant tinnitus. These are the same techniques that are used to preserve residual hearing: adaptive cochleostomy (adapting the cochleostomy to the patient’s cochlear anatomy and the configuration of the electrode to be implanted) and meticulous attention to the electrode insertion trajectory (to avoid deflection of the electrode tip into S. vestibuli.)
·When CI electrodes ruptured intrascalar partitions and traversed between the scala, tinnitus had a 16% chance of being generated or becoming worse.
·When electrodes did not traverse scala, tinnitus was not made worse.
(Please see the original paper for a breakdown of all groups and all data. There is interesting information about which electrodes tend to traverse scala and tinnitus suppression differences between peri-modiolar and anti-modiolar electrodes.)
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7. Ingo Todt, Grit Rademacherb, Sven Mutzeb, Ravi Ramalingam, Selene Wolter, Philipp Mittmann, Jan Wagner & Arne Ernst. Relationship between intracochlear electrode position and tinnitus in cochlear implantees. Acta Oto-Laryngologica 2015;8.
8. Eshraghi AA1, Yang NW, Balkany TJ. Comparative study of cochlear damage with three perimodiolar electrode designs. Laryngoscope. 2003 Mar;113(3):415-9.