Resection of Vestibular Schwannoma Through Middle Cranial Fossa Approach with Endoscopic Assistance.

OBJECTIVE: We sought to report the outcome of resection of vestibular schwannomas (VSs) originating from the inferior vestibular nerve that extended into the fundus of the internal auditory canal through the middle cranial fossa (MCF) approach with endoscopic assistance. METHODS: Seven patients with VSs who underwent resection through MCF approach with endoscope assistance and 12 patients with conventional microsurgery in our department were enrolled in this study. These patients' characteristics were acquired, and the surgical outcomes, as well as postoperative complications, were evaluated. RESULTS: In the endoscope group, the VS was first removed by a conventional microscopic procedure and then an endoscope was used to find and remove any residue lesions. In 3 of 7 patients, residue tumor in the space below transverse crest was found and completely removed under endoscope. Six of 7 patients (85.7%) had House-Brackmann grade I at the time of last follow-up in the endoscope group compared with 10 of 12 patients (83.3%) in the conventional microsurgery group. Serviceable hearing was successfully maintained in 2 of 3 patients (66.7%) in the endoscope group compared with 6 of 10 patients (60%) in the conventional microsurgery group. Total resections were achieved in all the patients (100%) in the endoscope group compared with 9 of 12 patients (75%) in the conventional microsurgery group. CONCLUSIONS: Using an endoscope in VS resection through the MCF approach could facilitate complete removal of the lesion while minimizing the risk of hearing loss and facial paralysis. The endoscope-assisted MCF approach is especially suitable for removing an intracanalicular VS with lateral extension involving the space below the transverse crest.

Morphological changes associated with low-tone hearing loss in guinea pig models of early endolymphatic hydrops / 生理学报

The present study was to explore the functional and morphological changes in cochleas of guinea pig models of early endolymphatic hydrops. Thirty albino guinea pigs were randomly divided into three groups: control, 4-week model and 8-week model groups. For each group, n = 10. Model groups were operated on the right ears to result in endolymphatic hydrops with the method of slight destruction of endolymphatic sac and duct from extradural posterior cranial fossa approach, and the animals in control group were sham operated. Electrocochleogram recorded by trans-tympanic approach and auditory brainstem response (ABR) were tested in preoperative model groups, control group, 4-week model group and 8-week model group to assess the hearing changes. Histologic morphometry was used to quantify hydrops by testing scala media area (SMA) ratio. Scanning electron microscope was used to assess the changes of cochlea hair cells. The results showed that the summating potential/compound action potential (SP/AP) ratio of electrocochleogram in 4-week model group (0.33 ± 0.14) and 8-week model group (0.43 ± 0.14) increased significantly, compared with that in control group (0.07 ± 0.06). The maximum SMA ratio in 4-week model group (2.64 ± 0.10) and 8-week model group (3.54 ± 0.13) increased significantly, compared with that in control group (1.06 ± 0.08). The results of maximum SMA ratio correlated with SP/AP ratio of electrocochleogram (r = 0.86). The results of hearing threshold of ABR revealed that the operated ears of model groups were higher than the preoperative results at frequencies of 2 kHz and 4 kHz. And the damage of cochlea hair cells in operated ears occurred in apical and subapical turns. These results suggest the increased SP/AP ratio of electrocochleogram can indicate early endolymphatic hydrops. There is low-tone hearing loss in guinea pig models of early endolymphatic hydrops, and it may be associated with the abnormalities of the stereocilia among the outer hair cells in operated ears which occurs in apical and subapical turns.