Neuronavigation for arteriovenous malformation surgery by intraoperative three-dimensional ultrasound angiography

Neuronavigational devices have traditionally used preoperative imaging with limited possibilities for adjustment to brain shift and intraoperative manipulation of the surgical lesions. We have used an intraoperative imaging and navigation system that uses navigation on intraoperatively acquired three-dimensional ultrasound data, as well as preoperatively acquired magnetic resonance imaging scans and magnetic resonance angiograms. The usefulness of this system for arteriovenous malformation (AVM) surgery was evaluated prospectively.

Nine consecutive patients with Spetzler Grade 1 (n = 3), 2 (n = 3), 3(n = 2) or 4 (n = 1) AVMs underwent operation using this intraoperative imaging and navigation system. The system provides real-time rendering of three-dimensional angiographic data and can visualize such projections in a stereoscopic (virtual reality) manner using special glasses. The experiences with this technology were analyzed and the outcomes assessed. Angiographic reconstructions of three-dimensional images were obtained before and after resection.

Conventional navigation on the basis of preoperative magnetic resonance angiography was helpful to secure positioning of the bone flap; stereoscopic visualization of the same data represented a powerful means to construct a mental three-dimensional picture of the extent of the AVM and the feeder anatomy even before skin incision. Intraoperative ultrasound corresponded well to the intraoperative findings and allowed confirmation of feeding vessels in surrounding gyri and rapid identification of the perinidal dissection planes, regardless of brain shift. The latter feature was particularly helpful because the intraoperative navigational identification of surgical planes leads to minimal exploration into the nidus or dissection at a greater distance from the malformation. Application of the system was thought to increase surgical confidence. In two patients, postresection ultrasound prompted additional nidus removal. Ultrasound angiography seemed to allow some degree of resection control, although its sensitivity was not thought to be sufficient. All AVMs were radically removed without new permanent morbidity.

The complexities of handling the pathological vessels of AVMs were ameliorated by intraoperative three-dimensional ultrasound and navigation because the three-dimensional outline of the vasculature (feeders, nidus, and draining veins) provided a means to adapt resection strategies, define dissection planes, and interpret intraoperative findings. It is difficult to provide a scientifically valid definition of "added value." However, in our experience, the added confidence and the improved mental image of the lesion that resulted from this technology improved the quality and flow of surgery.