Hearing preservation postsurgery by tumor type was as follows: 1A, 92%; 1B, 88%; 1C, 100%; 2A, 83%; 2B, 92%; and 3, 57%. Combined, this represents a hearing preservation rate of 87% after surgical treatment of Grade II acoustic neurinomas. Full nerve function was maintained in 88% of patients with anatomically preserved facial nerves in both Grade I and II tumors. The remaining 12% of patients retained partial function of the facial nerve. Two patients in the series lost anatomical integrity of the nerve due to surgery.

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An infrared based frameless stereotactic navigation device (Easy Guide Neuro) was investigated for its clinical applicability, registration/application accuracy and limitations in a standard operating room set-up. In a five-month period 40 frameless stereotactic procedures (23 female, 17 male, mean age 46.4, yrs range 10-83) including 36 craniotomies and 4 spinal surgery procedures were performed. Image registration, data transfer and operation planning using skin fixed fiducials (between 5-10, mean 6.6) and CCT in 12 patients/MRI in 28 patients, generally was done the day before surgery. Clinical applicability was proven in all procedures with an additional time for pre-operative imaging and system application in the OR of 50 min mean (35-120 range). A useful registration was achieved in 39/40 patients (97.5%) with a registration accuracy of 3.4 mm (range 1.8-6.7) for brain surgery cases and 14.4 mm (6.8-25) for spine cases. This resulted in intra-operative application accuracy values for brain surgery of 4.2 mm mean (range 1-12). Enhanced registration/application accuracy values over the test period from 4.2/3.8 mm mean (Cases 1-20) up to 3.2/2 mm mean (Cases 21-40) was observed. In spinal surgery an application accuracy of 11.3 mm mean (range 5-20) was found. An intra-operative re-calibration because of system-head drift was necessary in none of the patients, nevertheless, application accuracy degradation due to brain shift was detected in every case. In conclusion, the system allowed a time sufficient accurate frameless intra-operative localisation guidance in cavernoma, meningioma, glioma, and brain metastasis surgery. In spinal surgery, the application accuracy exceeded clinical usefulness due to high registration inaccuracy using skin markers.

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Regarding to the upcoming techniques in neuroendoscopy the IVth ventricle was examined. First in a series of 30 fresh and fixed anatomical specimens-the vessels injected with LATEX-the fourth ventricle was investigated endoscopically. There are three possibilities to reach the IVth ventricle: coming from the IIIrd ventricle via the aqueductus cerebri, using the basal cisterns through the apertura lateralis Luschkae and coming via the cerebellomedullar cistern through the foramen of Magendi. Using different kinds of endoscopes (rigid, flexible and steerable flexible)-diameter ranging from 5 to 9 french-with different optical systems (0 degree, 5 degrees, 30 degrees, 75 degrees) and different light sources (Halogen, Xenon) the anatomical details seen under the endoscope and the topographical landmarks of the approaches were investigated, presented and discussed. Based on the experience at the end of the cadaver work a short comment on which kind of equipment seems the best was given. A series of 14 clinical cases was presented as the second part of the study (7 cases with a tumor in the IVth ventricle-2 metastasis, 3 gliotic tumors, 1 ependymoma, 1 medulloblastoma, 3 patients with an occluded aqueduct because of meningo-ventriculitis and 4 patients with cystic malformations). The neuroendoscopic approaches, the neuroanatomical details relevant for surgery and the clinical data will be given and discussed. In general no intraoperative or postoperative complications were seen. In conclusion our experience from the theoretical neuroanatomical and the clinical part as well as the advantages and disadvantages from the different kind of endoscopes and approaches are discussed.