Primary afferent projections from singular parts of the vestibular labyrinth were studied in the guinea pig. The posterior ampullary nerve, the common trunk of the anterior and lateral ampullary nerves, as well as fibers innervating the macula sacculi or the macula utriculi were traced with crystals of horseradish peroxidase (HRP) lyophilisate. Posterior, as well as anterior and lateral ampullary fibers were found to project extensively to the superior vestibular nucleus, but also reached the other main vestibular nuclei. Saccular fibers projected mainly to the lateral parts of the lateral vestibular nucleus and to the adjoining descending and superior vestibular nuclei as well as to group y. Modest projections could be followed to the medial vestibular nucleus. Furthermore, a distinct saccular projection to the cochlear nuclei was evident. Utricular projections reached the four main vestibular nuclei with a denser accumulation of fibers within ventral parts of the lateral, descending and superior vestibular nuclei.
Objectives: The use of three-dimensional navigation systems provides information on the structures surrounding the field of operation and thereby reduces the risk of iatrogenic damage. The computed tomography (CT) data conventionally used are provided by preoperative scanning procedures, which means that tissue changes coming about during surgery are not seen on the screen. An intraoperative CT scanning procedure being able to update the CT data could provide a solution. Study Design: Endoscopic s inus operations using an intraoperative CT updating the three-dimensional navigation system were performed on six persons to find out, whether the above is true. Methods: Different parameters, advantages, and disadvantages in the cases of these six patients were compared with a group of 22 patients who underwent conventional endoscopic sinus surgery with different three-dimensional navigation systems without updating the CT data set. Results: The intraoperative CT for updating the three-dimensional navigation system provides useful information for the surgeon. Conclusion: Balancing its advantages against its disadvantages, the updating of the CT data set with intraoperative CT cannot be recommended for conventional standard endoscopic s inus surgery.
Three-dimensional navigation systems are routinely used in endoscopic skull base surgery, neurosurgery, maxillo-facial and endoscopic sinus surgery. Their precision can, however, change in the course of one experiment. We have compared five different 3D navigation systems and discuss here possible reasons for the limits of system precision. A plexiglass cube on which test points were marked served as a test-model. Two well-trained system users measured the distances between the test points in each of the five systems. The results were compared with reference data provided by the NUMEREX device at the Technical University of Vienna. The accuracy data shown by all these 3D navigation systems ranged from 0.0 mm to 6.67 mm. The accuracy data of a system calculated in advance did not always correspond with the system precision on the screen. The system precision in the center of the cube was higher than on its surface, which made us conclude that the angle between the tracker system and the pointing device touching the test point may be critical for system precision. Applying an automatic registration step did not result in greater system precision. Slice thickness and the angle of the pointing device seem to be responsible for system precision.
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