Volumetric anatomical and functional identification in neuronavigation

Abstract

In its third decade of development, neuronavigation has matured from pure trajectory planning to an instrument that can provide instant anatomical orientation on basis of three-dimensional (3D) images that closely match the microsurgical field at hand. Functional tissue properties may be incorporated in these images and volumetric rendering allows for visualization of all significant anatomical landmarks in the surgical path in one single view by modulating the opacity of overlying tissue layers. We have explored the possibilities of image guidance based on multimodal 3D images in more than 200 neurosurgical cases, with pathologies ranging from supratentrial tumors to lesions in the skull base and craniocervical junction. MRI (1.5 and 3 T), fMRI, positron emission tomography (PET), computed tomography (CT), CT angiography, and postmyelographic CT have been employed. Target registration error (TRE) and intraoperative shift have been calculated, and time and cost efficiency were estimated. 3D imaging was advantageous for fast orientation in complex morphology (gyri, sulci, dural sinuses, Circle of Willis, nasal cavity and paranasal sinuses), especially in cases where rotation of the operative field of view was necessary during the approach. Depiction of anatomical detail was limited by image resolution and tissue contrast. Virtual and real microscopic individual anatomy could permanently be correlated during surgery. Profound anatomical knowledge as well as repeated assessment of navigation errors was indispensable to detect accuracy changes during surgery. While guidance based on three-dimensional images cannot replace anatomical knowledge and surgical experience it offers a déjà vu experience for the neurosurgeon when the 3D model truly matches the surgical path and field. It relieves surgeons of the task of having to mentally reconstruct and rotate triaxial 2D images, extends their field of view beyond tissue barriers and provides functional information on the operative field that is otherwise invisible and inaccessible. Volumetric anatomical and functional identification based on image-guidance in the operating suite may expand surgical vision and improve patient safety—a major factor in cost-efficiency calculations.