The American journal of otology
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The histopathologic consequence of removing and reimplanting intracochlear electrode arrays on residual auditory nerve fibers is an important issue when evaluating the safety of cochlear prostheses. The authors have examined this issue by implanting multichannel intracochlear electrodes in macaque monkeys. Macaques were selected because of the similarity of the surgical technique used to insert electrodes into the cochlea compared to that in humans, in particular the ability to insert the arrays into the upper basal turn. ⋯ These electrodes did not appear to evoke a more extensive tissue response or result in more extensive neural degeneration compared with electrodes located within the scala tympani. In conclusion, the present study has shown that the reimplantation of a multichannel scala, tympani electrode array can be achieved with minimal damage to the majority of cochlear structures. Increased insertion trauma, resulting in new bone formation and spiral ganglion cell loss, can occur in the lower basal turn in cases where the electrode entry point is difficult to identify due to proliferation of granulation and fibrous tissue.
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Malignant hyperthermia is a seemingly rare genetic myopathy. Hypermetabolic crisis accompanied by a rise in body temperature to as high as 44 degrees C is its hallmark. Malignant hyperthermia is usually triggered by potent inhalational anesthetics and/or depolarizing muscle relaxants. ⋯ The contracture study was positive in six of the seven patients studied. No anesthetic or surgical complications were encountered. This study demonstrates that patients at risk of developing malignant hyperthermia crisis can have otologic surgical procedures performed safely while undergoing appropriately selected general anesthesia.
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Direct facial nerve stimulation and monitoring during cerebellopontine angle (CPA) tumor surgery are critical for identification and preservation of function. Electrically evoked facial nerve monitoring was compared with ulnar train-of-four monitoring under progressive neuromuscular blockade. Using a rabbit model, the facial nerve function of six controls was compared to that of six specimens with acute or chronic injuries. ⋯ The results of this study support the hypothesis that high degrees of neuromuscular blockade do not preclude satisfactory EMG monitoring of the facial nerve during CPA tumor surgery. This study did demonstrate that chronically injured facial nerves may show greater sensitivity to the effects of neuromuscular blockade. Lower levels or avoidance of neuromuscular blockade should be employed under these circumstances.
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The recent discovery of hair cell regeneration in the avian inner ear raises the possibility that hair cell regeneration might occur in the mammalian cochlea as well. The authors used 3H-thymidine labeling to detect mitotic activity in the cochleas of normal 3-week old gerbils exposed to acoustic trauma. Following an acoustic insult that caused progressively more severe damage in an apical to basal progression, 3H-thymidine was injected for 5 days. ⋯ Three labeled cells were seen in intercellular spaces within the sensory epithelium; they appeared to be macrophages. Frequent cell division was seen in numerous other regions of the damaged cochleas and among glial cells adjacent to the acoustic nerve fibers. It is concluded that there is no evidence for hair cell regeneration following acoustic trauma in the gerbil, but acoustic trauma does induce cell division in numerous other areas of the cochlea.
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Case Reports
Hearing preservation following a transtemporal resection of an acoustic schwannoma: a case report.
The transtemporal or translabyrinthine approach is generally regarded as the most reliable method of ensuring total tumor removal and preservation of facial nerve function in the resection of a cerebellopontine angle tumor. This is particularly true in removing a tumor that has a significant extension into the patient's internal auditory canal. ⋯ We have encountered a patient, however, who was serially documented as having serviceable hearing after a transtemporal removal of an acoustic schwannoma. Plausible reasons for the functional preservation of some of this patient's hearing are included in the discussion.