Another evidence for pressure transfer mechanism in incomplete partition two anomaly via enlarged vestibular aqueduct.

A female patient with unilateral enlarged vestibular aqueduct (EVA) demonstrated scala vestibuli dilatation on that side while on the contralateral side both vestibular aqueduct and scala vestibuli were normal. This important radiological finding demonstrates that modiolar defects (hence 'cystic apex') observed in Incomplete partition-II is due to pressure transfer via EVA during embryological development. Therefore, it supports the previous histopathological ideas radiologically. Depending on the patency of EVA, variety of modiolar defects may arise.

Post Hybrid Cochlear Implant Hearing Loss and Endolymphatic Hydrops.

OBJECTIVE: To evaluate for potential causes of delayed loss of residual hearing that variably occurs with hybrid cochlear implants. STUDY DESIGN: Histopathological evaluation of 29 human temporal bone (HTB) with cochlear implant (CI). SETTING: The Neurotology and House HTB Laboratory of UCLA (House-UCLA). SUBJECTS AND METHODS: HTB from CI patients from the House-UCLA HTB Laboratory (n = 28) and one courtesy of Massachusetts Eye and Ear Infirmary (MEEI). Histopathological analysis to identify the location of cochleostomy, fibrosis, and bone formation in the scala vestibuli and tympani, and endolymphatic hydrops. Spiral ganglion neuron counts were obtained. Statistical analysis compared presence of cochleostomy and location with the histopathological findings. RESULTS: Seventeen of 29 bones with fibrosis in the scala vestibule (SV) and tympani had evidence of a cochleostomy involving the SV containing the ductus reunions, all of which had hydrops. Ten of 11 bones had no SV fibrosis, and a cochleostomy limited to the scala tympani, of which all had no hydrops. One HTB had moderate SV fibrosis not involving the ductus reuniens, and was without hydrops. One HTB had a SV cochleostomy but the electrode ruptured Reissner's membrane, and was without hydrops. Cochleostomy was significantly associated with SV fibrosis and hydrops (p < 0.01), those without hydrops had no SV atrophy (p < 0.01). Round window insertion was associated with no fibrosis and no hydrops. CONCLUSION: We hypothesize that cochleostomies involving scala vestibuli incite fibrosis, compromising the ductus reuniens, causing hydrops which may cause the delayed loss of residual low frequency hearing in CI.

Effect of KTP laser cochleostomy on morphology in the guinea pig inner ear.

BACKGROUND: The main advantage of using the KTP (potassium-titanyl-phosphate) laser for stapedotomy instead of the conventional micropick instrument is the smaller risk for mechanical damage. However, the KTP laser could theoretically inflict damage to inner ear structures. We hypothesize that KTP laser light [wavelength (λ) = 532 nm] is hardly absorbed in perilymph but well absorbed in solid structures. The aim of this pilot study was to assess if damage occurred after KTP laser cochleostomy in an animal model and, if so, to what extent and at which settings. MATERIALS AND METHODS: In six guinea pigs, a KTP laser cochleostomy at the basal turn was created. Laser settings of 1, 3 and 5 W and 100 ms pulse time (n = 2 each) were used. Histological preparations were studied for damage to neuroendothelial cells and intrascalar blood. RESULTS: No damage to inner ear neuroendothelial cells was observed, even at the highest power. Blood clots in the scala tympani from vessels in the cochlear wall were seen. The effects were minimal in the lowest, currently clinically used settings. CONCLUSION: KTP laser cochleostomy gives no damage to inner ear neuroendothelial cells but may cause intrascalar hemorrhages.

A safety evaluation of dexamethasone-releasing cochlear implants: comparative study on the risk of otogenic meningitis after implantation.

CONCLUSION: Dexamethasone released from a cochlear implant seems not to enhance the risk for postoperative infections. OBJECTIVE: Dexamethasone has a positive impact on hearing preservation for electric acoustic stimulation (EAS). Due to their antiproliferative and immunosuppressive properties, steroids may enhance the risk of postoperative infections. A comparative study was performed to evaluate the risk of pneumococcal meningitis after implantation of dexamethasone-eluting cochlear implants. METHODS: Thirty guinea pigs were implanted with non-eluting (n = 15) or dexamethasone-eluting (n = 15) cochlear implant electrode dummies. After 5 weeks, animals were exposed to a virulent strain of Streptococcus pneumoniae. The two groups were compared based on the meningitis rate. Animals were observed for 5 days for signs of meningitis. Meningitis was verified by clinical outcome as well as by pleocytosis and presence of bacteria in cerebrospinal fluid. Results were confirmed by histological examination of brains and cochleae, clinical findings and culture. RESULTS: There was no significant difference in meningitis risk between the two groups. In the group with non-eluting implants, 3 of 15 animals developed meningitis, while in the group with dexamethasone-eluting implants 4 of 15 showed signs of meningitis. In this study dexamethasone-releasing implants did not significantly increase the risk of postoperative pneumococcal otogenic meningitis.

Cochlear third window in the scala vestibuli: an animal model.

BACKGROUND: Pathologic third window has been investigated in both animals and humans, with a third window located in the vestibular apparatus, specifically, dehiscence of the superior semicircular canal, serving as the clinical model. HYPOTHESIS: The present study sought to examine the effect of a cochlear third window in the scala vestibuli on the auditory thresholds in fat sand rats that have a unique anatomy of the inner ear that allows for easy surgical access. METHODS: The experiment included 7 healthy 6-month-old fat sand rats (a total of 10 ears). A pathologic third window was induced by drilling a hole in the bony labyrinth over the scala vestibuli, with preservation of the membranous labyrinth. Auditory brainstem responses to high- and low-frequency acoustic stimuli delivered via air and bone conduction were recorded before and after the procedure. RESULTS: In the preoperative auditory brainstem response recordings, air-conduction thresholds (ACTs) to clicks and tone bursts averaged 9 and 10 dB, respectively, and bone-conduction thresholds averaged 4.5 and 2.9 dB, respectively. Postfenestration ACTs averaged 41 and 42.2 dB, and bone-conduction thresholds averaged 1.1 and 4.3 dB. The change in ACT was statistically significant (p < 0.01). CONCLUSION: The presence of a cochlear third window in the scala vestibuli affects auditory thresholds by causing a decrease in sensitivity to air-conducted sound stimuli. These findings agree with the theoretical model and clinical findings.

Spiral ganglion degeneration patterns in endolymphatic hydrops.

OBJECTIVES: The mechanistic association between endolymphatic hydrops (ELH) and hearing loss (HL) is unclear. Although ELH severity has been shown to correlate in some studies with HL, injury of vital structures, including hair cells and the cochlear nerve, have failed to demonstrate correlation with ELH severity. The goal of this study is to evaluate the hypothesis that spiral ganglion cell degeneration is the principle pathologic site of ELH-related cochlear injury, correlates with ELH severity, and is most profound in the apical region. STUDY DESIGN: Surgical induction of ELH in the guinea pig model was followed by histologic confirmation of ELH and subsequent correlation with segmental spiral ganglion cell densities. METHODS: Guinea pigs (N = 14) were subjected to unilateral ELH induction and killed after 4 to 6 months. ELH severity and spiral ganglion densities were obtained using computer-aided morphometric analysis. Densities were normalized by calculating a spiral ganglion degeneration index (DI) for each animal. RESULTS: The apical spiral ganglion demonstrated significantly greater degeneration than that noted in the basal spiral ganglion (DI: 1.93 vs. 1.13; P = .004). The degree of spiral ganglion degeneration in the apex correlates well with a total hydrops index (P = .006) and an apical hydrops index (P = .003). Basal spiral ganglion degeneration however, does not correlate well with hydrops severity (total hydrops index: P > .05; basilar hydrops index: P > .05). CONCLUSIONS: ELH-related pathology appears to focus initially on the apical spiral ganglion and the degree of deterioration correlates well with the severity of ELH. These findings mirror some reports in the human condition, and imply that the mechanism of cochlear injury in ELH and secondary dysfunction appears to be a neural toxicity that begins in the apex of the cochlea.