TECHNIQUES AND APPLICATIONS OPERATION OF ARTERIOVENOUS MALFORMATIONS ASSISTED BY STEREOSCOPIC NAVIGATION- CONTROLLED DISPLAY OF PREOPERATIVE MAGNETIC RESONANCE ANGIOGRAPHY AND I NTRAOPERATIVE ULTRASOUND ANGIOGRAPHY Geirmund Unsgaard, Ph.D., M.D. Department of Neurosurgery, Trondheim University Hospital, and Norwegian University of Science and Technology, Trondheim, Norway Steinar Ommedal, B.Sc. SINTEF Health Research, Trondheim, Norway Ola M. Rygh, M.D. Department of Neurosurgery, Trondheim University Hospital, and University of Science and Technology, Trondheim, Norway Frank Lindseth, Ph.D. SINTEF Health Research, Trondheim, Norway Reprint requests: Geirmund Unsgaard, Ph.D., M.D., University Hospital of Trondheim, Olav Kyrres Gate 17, N-7005 Trondheim, Norway. Email: geirmund.unsgard@medisin.ntnu.no Received, July 2, 2004. Accepted, December 2, 2004. OBJECTIVE: To study the application of navigated stereoscopic display of preoperative three-dimensional (3-D) magnetic resonance angiography and intraoperative 3-D ultrasound angiography in a clinical setting. METHODS: Preoperative magnetic resonance angiography and intraoperative ultra- sound angiography are presented as stereoscopic images on the monitor during the operation by a simple red/blue technique. Two projections are generated, one for each eye, according to a simple ray casting method. Because of integration with a naviga- tion system, it is possible to identify vessels with a pointer. The system has been applied during operations on nine patients with arteriovenous malformations (AVMs). Seven of the patients had AVMs in an eloquent area. RESULTS: The technology makes it easier to understand the vascular architecture during the operation, and it offers a possibility to identify and clip AVM feeders both on the surface and deep in the tissue at the beginning of the operation. All 28 feeders identified on the preoperative angiograms were identified by intraoperative navigated stereoscopy. Twenty-five were clipped at the beginning of the operation. The other three were clipped at a later phase of the operation. 3-D ultrasound angiography was useful to map the size of the nidus, to detect the degree of brain shift, and to identify residual AVM. CONCLUSION: Stereoscopic visualization enhances the surgeon’s perception of the vascular architecture, and integrated with navigation technology, this offers a reliable system for identification and clipping of AVM feeders in the initial phase of the operation. KEY WORDS: Arteriovenous malformation, Brain shift, Intraoperative imaging, Neuronavigation, Resection control, Sonography, Stereoscopic visualization, Three-dimensional ultrasound Neurosurgery 56[ONS Suppl 2]:ONS-281–ONS-290, 2005 DOI: 10.1227/01.NEU.0000157005.51053.41 W e have available a navigation sys- tem with a module for navigated stereoscopic display of preopera- tive magnetic resonance angiography (MRA) and intraoperative ultrasound angiography (Doppler). The potential applications for this module are surgery on tumors close to or surrounding important vessels, aneurysm sur- gery, and especially arteriovenous malforma- tion (AVM) surgery because of the challeng- ing angioarchitecture of AVMs. We report here our initial experiences with navigated stereoscopy in AVM surgery. Different modalities are available for treat- ing AVMs. Radiosurgery seems to be the best way to treat small and deep-seated AVMs, especially in eloquent areas, but the risk of hemorrhage remains until the AVM is com- pletely closed (3). AVMs may also be treated by embolization. Alone, this technique is usu- ally not sufficient to completely close AVMs (8). Eventually, new large feeders will develop from small feeding vessels that are impossible to reach by embolization (12). Embolization is therefore used primarily in combination with microsurgery or radiosurgery. Despite the de- velopment of the embolization and radiosur- gery technique, microsurgical resection re- mains an important treatment modality for AVMs (5). Surgical resection can be a rather challeng- ing procedure, especially if the AVM is large NEUROSURGERY VOLUME 56 | OPERATIVE NEUROSURGERY 2 | APRIL 2005 | ONS-281