PubMed · 3814405
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L Terr. 1987. Fusiform-shaped cells.. https://doi.org/10.1001/archotol.1987.01860040101035
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OBJECTIVE: The exact mechanism of hearing loss, the most common presenting symptom in patients with vestibular schwannomas, remains unclear. To test whether increased pressure in the internal auditory canal from tumor growth is responsible for this clinical finding, the intracanalicular pressure in patients harboring these tumors was measured. STUDY DESIGN: Prospective study. SETTING: Tertiary referral hospital. PATIENTS: Fifteen consecutive patients undergoing a retrosigmoid approach for resection of vestibular schwannomas were included in the study. INTERVENTION: The intracanalicular pressure in every patient was measured by introducing a pressure microsensor into the internal auditory canal. The pressure readings, which were performed before tumor resection, were then correlated with tumor size and respective preoperative hearing status. RESULTS: Placement of the pressure monitor into the internal auditory canal revealed a biphasic waveform in every patient. Whereas the mean intracanalicular pressure was 20 mm Hg, there was significant variability among patients (range, 1-45 mm Hg). The intracanalicular pressure directly correlated with the amount of tumor in the internal auditory canal (r > 0.63, p < 0.012) but not with the total tumor size (r </= 0.40, p > 0.075). Furthermore, eight patients with class A preoperative hearing (American Academy of Otolaryngology-Head and Neck Surgery classification) had lower intracanalicular pressures than did five patients with class B hearing (16 +/- 5 vs. 28 +/- 4). Although this observation suggested an inverse correlation between the intracanalicular pressure and hearing function, the difference between the two groups was not statistically significant (p = 0.14). CONCLUSION: Pressure on the cochlear nerve as a result of tumor growth in the internal auditory canal may be responsible for hearing loss in patients with vestibular schwannomas. Modification of surgical techniques to address the elevated intracanalicular pressure may be beneficial in improving hearing preservation in these patients.
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The purpose of this study was to evaluate possibilities and technical risks for combining intended electrical stimulation of the cochlear nerve and functional magnetic resonance imaging (fMRI). Theoretical considerations and experiments indicate that fMRI can be performed safely during electrical stimulation. A nerve stimulator was developed with minimized length of electrical conductors, current limiting resistance, high inner impedance of a current source, radio frequency (RF)-shielding, and avoidance of ferromagnetic materials. This nerve stimulator transfers the optically encoded stimulating current signal via a fiber optic cable located near the area of stimulation. There, the optical signal drives an MRI-compatible current source. This set-up was tested with transtympanic electrical stimulation of the cochlear nerve at the promontory during an fMRI examination. No hazardous effects could be detected. The stimulation resulted in activation of the Heschl's gyrus. Compared to the conventional promontory testing this method may allow a more objective examination of cochlear implant candidates. Magn Reson Med 42:371-378, 1999.