Are tinnitus burden and tinnitus exacerbation after cochlear implantation influenced by insertion technique, array dislocation, and intracochlear trauma?

Abstract

Introduction: Although numerous studies suggest that cochlear implantation (CI) generally alleviates the overall burden of tinnitus, certain patients experience tinnitus exacerbation following CI. The exact cause of this exacerbation is still uncertain. This prospective study aimed to investigate whether cochlear trauma, resulting from scalar dislocation of the electrode array, affected postoperative tinnitus intensity, tinnitus burden, and speech perception. Additionally, the influence of CI insertion technique, insertion depth, insertion angle, and cochlear morphology on postoperative tinnitus was assessed.

Methods: We evaluated 66 CI recipients preoperatively at 2 days, 4 weeks, and 12- and 24-months following surgery. Digital volume tomography was employed to document scalar position, insertion depth, and cochlear morphology postoperatively. Speech perception was analyzed using Freiburg monosyllables. The tinnitus burden was evaluated using the tinnitus questionnaire, while the tinnitus intensity was quantified using a visual analog scale.

Results: Study results pertaining to tinnitus intensity and burden did not reveal a significant difference in elevation regarding scalar position and dislocation after CI surgery compared to preoperative tinnitus levels. However, dislocation was only identified in four patients, and scala vestibuli insertions were observed in two patients. Comparing preoperative and 1-year postoperative outcomes, CI was noted to substantially reduce the tinnitus burden. When the speech processor was worn, the tinnitus intensity was significantly diminished. In comparison to round window (RW) insertion, the insertion technique cochleostomy (CS) did not exhibit a significant difference or a trend toward increased tinnitus intensity.

Conclusion: This study demonstrates that CI significantly decreases the tinnitus burden. The observation implies that the electrical stimulation of the auditory pathway, facilitated by wearing the speech processor, significantly reduced the tinnitus intensity. The incidence of dislocations and scala vestibuli insertions has declined to the extent that it is no longer feasible to formulate statistically significant conclusions.

Keywords: anatomy; cochlea; cochlear implant; psychometry; tinnitus.

Figure 1

Study plan of tinnitus assessment at different time points after CI implantation: preoperative (pre.o.), 2 days postoperative (2d p.o.), 4 weeks postoperative (4w p.o.), 1 year postoperative (1y p.o.), and 2 years postoperative (2y p.o.). Assessment tools were the tinnitus questionnaire (TQ), visual analog scale (VAS), and aided and unaided Freiburg speech intelligibility test (FSIT).

Figure 2

The tinnitus burden evaluated with the TQ total (left side) significantly decreased following CI comparing preoperative results and TQ total 1 year postoperatively. Differentiating the TQ subscales (right side), most aspects of tinnitus burden improve significantly 1 year postoperatively compared to preoperative. *p < 0.05 marked in bold. Sample size (n): TQ pre.o. n = 60; 4w p.o. n = 55; 1y p.o. n = 28.

Figure 3

(A) The tinnitus intensity itself did not reduce significantly following CI surgery comparing preoperative results with the VAS evaluated 2 days, 4 weeks, 1 year, and 2 years postoperatively. (B) However, if patients wore the speech processor, tinnitus intensity was significantly reduced (2 years postoperative evaluation). *** p < 0.001. Sample size (n): VAS pre.o. n = 66; 2d p.o. n = 65, 4w p.o. 58; 1y p.o. n = 28; 2y p.o. n = 31.

Figure 4

(A) Tinnitus intensity did not change significantly comparing the patients that underwent CS (=cochleostomy), RW (= round window) insertion, and ERW (=extended round window) insertion. (B) Similarly, the tinnitus burden did not change significantly comparing the patients who underwent CS, RW, and ERW. Sample size (n): RW pre.o. n = 48; 2d p.o. n = 44; 4w p.o. n = 23; 1y p.o. n = 28; 2y p.o. n = 28. CS pre.o. n = 8; 2d p.o. n = 6; 4w p.o. n = 6; 1y p.o. n = 5; 2y p.o. n = 4. ERW pre.o. n = 2; 2d p.o. n = 2; 4w p.o. n = 2; 1y p.o. n = 0; 2y p.o. n = 1.

Figure 5

Dislocation of the electrode array did not show significantly increased tinnitus intensity (A) or tinnitus burden (B). Sample size (n): non-dislocated pre.o. n = 54; 2d p.o. n = 48; 4w p.o. n = 50; 1y p.o. n = 24; 2y p.o. n = 29. Dislocated pre.o. n = 4; 2d p.o. n = 3; 4w p.o. n = 3; 1y p.o. n = 1; 2y p.o. n = 3.

Figure 6

(A) Correlation between tinnitus intensity and cochlear height before implantation and (B) 1 year after implantation. (C) Correlation between array insertion angle and tinnitus intensity 1 year postoperatively. (D) Correlation between array insertion depth and tinnitus intensity 1 year postoperatively.