Computer-Assisted Neurosurgery PDF

PREFACE

The practice of neurosurgery has been fundamentally changed by the evolution of the electronic computer. Digital imaging techniques such as computer-assisted tomography, magnetic resonance imaging, and digital angiography revolutionized diagnostic neurosurgery, supplanting pneumoencephalography, myelography, and many other invasive procedures. Although powerful diagnostic tools, these technologies have not replaced the diagnostician; rather they complement and confirm thoughtful deductions based on a careful neurologic history and examination.

In the late 1970s, several neurosurgical visionaries recognized that these computerized imaging systems were capable of more than just aiding diagnosis. They devised equipment and techniques to harness the spatial information contained within these images for surgical guidance. Image-guided frame stereotaxy used a stereotactic reference frame and imaging modality-specific encoders to allow safe, accurate biopsy of imaged brain lesions. This technique was adapted to numerous neurosurgical procedures including depth electrodes, functional neurosurgery, radiation implants, and craniotomy. Virtually any intracranial target could be accessed along predefined approaches or trajectories. Although the calculations to decode spatial information from neuroimaging could be done manually or with calculators, the availability of reasonably priced computers and workstations simplified the process for the surgeon.

As the ratio of computing power to cost increased, not only could points be defined stereotactically but volumes as well. Stereotactic radiosurgery and volumetric craniotomy benefited from these technological advances, but stereotactic craniotomy failed to be widely adopted in the neurosurgical community, perhaps as the benefit of guidance was not felt to outweigh the cumbersome logistics of the procedure.

In the early 1980s, three technological advances occurred that allowed for the development of stereotactic systems that were not reliant on applied reference frames: (1) neuroimaging had progressed to the point where it was not only spatially accurate within a given image (i.e., slice) but also accurate throughout the entire volume of data; (2) the availability of accurate, inexpensive three-dimensional digitizers; and (3) another incremental increase in low-cost computing power such that three-dimensional transformations and other calculations could be performed and displayed using image data sets several megabytes in size and done so in near real time. Image-guided frameless stereotaxy could not only provide the guidance information of its frame counterpart, but provided truly interactive navigational information such as location and orientation during surgical procedures. These devices could provide instantaneous intraoperative answers to the questions, ‘‘Where am I in this head?'' and ‘‘What's on the other side of that structure?''

Since then, these systems have become commonly known as surgical navigation systems or neuronavigation systems. Although surgical navigational systems have become mainstream devices, equally at home in the community as well as the academic medical center, far too many of these devices rest idle or are misused because the neurosurgeon has not been adequately exposed to the principles and nuances of computer-assisted neurosurgery beyond the information provided by a manufacturer's device or sales representative. The thrust of this book is not to dwell on the specifics of any given surgical navigational system (although a brief primer on surgical navigational system technologies is provided for the newcomer), but rather it is to provide a resource on these computerized surgical tools with emphasis on how they work (as well as their limitations) and how best to use them in a variety of clinical settings.

This follow-up to our previous book Image-Guided Neurosurgery: Clinical Applications of Surgical Navigation is divided into three sections: Basic Principles, Technologic Applications, and Clinical Applications. In Part I: Basic Principles, we review how these devices work starting with the process by which the computer relates image space to the three-dimensional space of the operating room—the so-called ‘‘registration'' process. We then examine the technologies that allow these systems to work, with an emphasis on how the location of surgical tools is relayed to the computer via various three-dimensional digitizers. Optimal use of navigation for many procedures requires preplanning a target and the course or trajectory to get there; various means of presenting this information to the surgeon in a useful fashion are presented. Intrinsic to knowing how to use a tool effectively is to understand its limitations and how it can malfunction; these are reviewed Chapter 4: Pitfalls.

Surgical navigations systems often work in concert with other technologies, and the same principles used for their use in the operating room apply to certain noninvasive radiosurgical tools. As intracranial surgery becomes progressively more complex and focused on maximal safe resection, surgical navigational systems are increasingly employing intraoperative imaging such as intraoperative magnetic resonance imaging, often in conjunction with neurophysiologic monitoring. The marriage of endoscopy with navigation has broadened the utility of these devices, not just for intraventricular procedures but also for some skull base and trans-sphenoidal operations and, perhaps, some day intraparenchymal tumors. This is explored in Part II: Technologic Applications.

In the end, however, the reasons for using surgical navigational systems are to augment or guide certain surgical procedures. General overviews of how surgical navigational systems can be used for brain biopsy, related procedures, and minimal access craniotomies are reviewed in Part III: Clinical Applications (including a narrated video on the CD-ROM accompanying this book). We then delve into the specifics of maximizing the value of surgical navigation in several clinical disorders such as gliomas, meningiomas, pituitary tumors, vascular malformations, spinal, seizure, and skull base neurosurgery.