The effect of systemic steroid on hearing preservation after cochlear implantation via round window approach: A guinea pig model

Abstract

This study aimed to evaluate the efficacy of perioperative systemic steroid administration and to compare the effects of its two postoperative administration periods, three days and seven days, for long-term hearing preservation after cochlear implantation via round window approach. Thirty Dunkin-Hartley guinea pigs were randomly segregated into three experimental groups: the control group (n = 10)

the 3-day infusion group receiving steroid for postoperative three days (n = 10)

and the 7-day infusion group receiving steroid for postoperative seven days (n = 10). All animals, regardless of group, received electrode insertion surgery. A slim straight dummy practice electrode for human (Cochlear Ltd, Lane Cove NSW, Australia) was inserted to a depth of 2.25 mm via a round window. A mini-osmotic pump (10μl/hr, Alzet, USA), filled with dexamethasone sodium phosphate (4mg/ml), was inserted subcutaneously 12 hours prior to electrode insertion, and removed three days or seven days after electrode insertion, depending on the group. The hearing thresholds (tone pips at 2, 8, 16, 24, 32 kHz) were measured four times—once prior to electrode insertion, and at 1 week, 4 weeks, and 12 weeks after electrode insertion—by an auditory brainstem response. Histologic evaluation of the cochlea was performed at 12 weeks after electrode insertion. At 4 weeks after electrode insertion, auditory brainstem response threshold shifts in the 7-day infusion group were significantly lower than the control group at all frequencies. The 7-day infusion group kept significantly better hearing preservation compared with the control group after 12 weeks of implantation. The tissue response, including fibrosis and ossification was significantly reduced in the 7-day infusion group compared with the control groups. The outer hair cells of the basal, middle and apical turns and inner hair cells of the basal and middle turns were preserved significantly more in the 7-day infusion group than in the control group. The spiral ganglion cell densities of the basal, middle and apical turns were significantly higher in the 7-day infusion group compared with the control group. Based on our results, it appears that there is an effective postoperative period that is optimal for hearing preservation after electrode insertion. Administration of perioperative systemic steroid during this period could contribute to residual hearing preservation.