A gerbil model of sloping sensorineural hearing loss.

OBJECTIVE: The goal of the overall project is to develop knowledge about cochlear physiology during cochlear implantation and develop procedures for assessing its status during hearing preservation surgery. As a step toward this goal, for this study, we established an animal model of sloping high frequency sensorineural hearing loss that mimics the hearing condition of candidates for combined electric-acoustic stimulation. METHODS: Mongolian gerbils were exposed to band-pass noise using various cutoff frequencies, intensities, exposure times, and survival times. Hearing loss was assessed in far-field recording using preexposure and postexposure auditory brainstem responses (ABRs), and in acute, near-field recordings of the cochlear microphonic and compound action potential from an electrode on the round window. Anatomic loss of hair cells was assessed from dissections. RESULTS: Postexposure ABRs and near-field recordings from the round window revealed sensorineural hearing loss that varied with the overall noise exposure. Loss of hair cells ranged from relatively sparse to large areas of complete absence depending on the noise exposure. Cases with high intensity (120 dB SPL) and long exposure times (3 h) showed sloping patterns of hearing loss with profound high-frequency loss and mild-to-moderate low-frequency loss. These cases showed complete loss of hair cells in the basal cochlea and preserved hair cells in the apical cochlea. The frequencies comprising the slope in the ABRs and the location of the transition zone between preserved and lost hair cells varied according to the cutoff frequency used. CONCLUSION: We were able to reliably induce sensorineural hearing loss and loss of hair cells in the gerbil that is comparable to candidates for hearing preservation surgery. This model can be used to evaluate the effects of electrode introduction in a system with a hearing condition similar to that in cases of hearing preservation operations.

Sinonasal quality-of-life before and after endoscopic, endonasal, minimally invasive pituitary surgery.

BACKGROUND: Endoscopic, endonasal, minimally invasive pituitary surgery (MIPS) has proven to be safe and efficacious. However, there are few data that assess the health-related or sinonasal-specific quality-of-life (QoL) of those undergoing MIPS. Our hypothesis is that patients undergoing MIPS do not have significantly different sinus disability or change in QoL after surgery compared to prior to surgery. METHODS: This is a retrospective review of patients undergoing MIPS between 2002 and 2009. Rhinosinusitis Disability Index (RSDI) scores, patient demographics, tumor characteristics, surgical outcomes, and intraoperative/postoperative complications were recorded. Preoperative and postoperative mean RSDI scores and the mean absolute change in RSDI were calculated with 95% confidence intervals (CIs). One-way analysis of variance (ANOVA) compared RSDI scores between different tumor subgroups. RESULTS: A total of 50 patients completed the RSDI preoperatively and postoperatively. Analyses revealed no significant difference between preoperative and postoperative scores across all domains (p = 0.84). When the cohort was stratified into functional vs nonfunctional tumor types there was no significant difference between the 2 groups (p = 0.88). Data showed no statistically significant change in RSDI scores postoperatively in all groups. CONCLUSION: These data show that MIPS with appropriate postoperative care results in little or no long-term sinonasal quality of life defects.

Intracochlear recordings of electrophysiological parameters indicating cochlear damage.

OBJECTIVE: : The pathophysiologic mechanisms resulting in hearing loss during electrode implantation are largely unknown. To better understand the functional implications of electrode implantation, we recorded the effects of cochlear damage on acoustically evoked intracochlear measurements using normal-hearing gerbils. METHODS: : A metal electrode was placed on the surface of the round window, and recordings of the cochlear microphonic (CM) and compound action potential (CAP) were made in response to stimulation with tone-bursts at various frequencies in 1-octave intervals and at intensities of 15 to 72 dB sound pressure level. The electrode was then advanced incrementally, with CM and CAP measurements obtained at each step. These data were compared with data obtained at the round window, and the electrode was withdrawn when a significant change was observed. After electrophysiological analysis, the cochlea was examined histologically. RESULTS: : Results show that on electrode insertion, loss of amplitude in the CM and CAP occurs after damage to cochlear structures. Loss of activity was typically first apparent in the CAP rather than the CM. CONCLUSION: : These results suggest that a reduction of the CAP can be an early marker of interaction of the electrode with cochlear structures. Such measurements are potentially available with slight modifications to current cochlear implant technology.

Correlation of early auditory potentials and intracochlear electrode insertion properties: an animal model featuring near real-time monitoring.

OBJECTIVE: The goal of this work was to assess electrophysiologic response changes to acoustic stimuli as an intracochlear electrode impacted cochlear structures in an animal model of hearing preservation cochlear implantation. The ultimate goal is to develop efficient procedures for assessing the status of cochlear physiology for intraoperative use. METHODS: Sixteen gerbils and 18 ears were tested. A rigid electrode was inserted through a basal turn cochleostomy and directed toward the basilar membrane/osseous spiral lamina complex. We recorded acoustically evoked early auditory potentials including cochlear microphonics (CMs) and compound action potentials (CAPs) to a short stimulation sequence consisting of one stimulus frequency and intensity as the electrode was advanced. A microendoscope was used to visualize the electrode insertion progress and to identify the site of electrode impact. After each experiment, the site of intracochlear trauma was confirmed using whole mount preparations. RESULTS: Electrophysiologic changes correlated well with the degree and location of trauma. We observed four distinct patterns. In addition, the endoscope in conjunction with the short recording sequence allowed for the detection of response changes that were reversible when the electrode was retracted. These cases were associated with less than full-thickness damage on histology. CONCLUSION: The short recording sequence to obtain acoustically evoked intracochlear potentials and the microendoscope allowed us to detect various levels of cochlear trauma including minor and reversible damage. Recordings of this type are potentially available using current implant technology. Future improvements in the measurements can be expected to improve the efficiency of the recording paradigm to produce a clinically useful tool.

Flexible cochlear microendoscopy in the gerbil.

OBJECTIVES/HYPOTHESIS: To validate the scientific utility of flexible cochlear microendoscopy in the gerbil. This model is currently being developed to study the effects of intracochlear electrode positioning on functional parameters. STUDY DESIGN: Animal experiments. METHODS: A flexible fiberoptic microendoscope featuring a light channel and an outer diameter of 0.4 mm was specially modified to allow intracochlear visualization. Specifically, the focus distance was reduced to 1 mm and the optical properties were modified so that visualization was adequate when submerged in perilymphatic fluid. This endoscope was used to view intracochlear contents and monitor the progress of electrode insertions in 11 gerbils. The endoscopic data estimating the site of damage were compared to postmortem microdissections. RESULTS: The endoscope allowed for adequate visualization of intracochlear content in all animals. The site of electrode contact seen in the endoscope was confirmed in the microdissected cochleae in 10 of 11 cases, indicating the endoscope's ability to correctly identify the site of intracochlear trauma in this animal model. CONCLUSIONS: The current report demonstrates the feasibility of intracochlear microendoscopy in an animal model of hearing preservation cochlear implantation.