Using advanced simulation technology for cranial base tumor evaluation.

Tumors of the skull base in general are considered one of the more difficult head and neck pathologic entities to treat surgically; some, in fact, consider lesions in this area inoperable. Close proximity to vital structures, such as cranial nerves, organs of special sensation, such as the eye and inner ear, major vascular structures to the brain, and the brain itself make operating in this area extremely challenging even for the "experts." In the past, injury to nearby vital structures led to unacceptable operative morbidity, and surgical mortality was overwhelming, secondary to hemorrhage and sepsis. Both led to understandable fear and trepidation on the part of our surgical forefathers. Only within the recent past has surgical treatment of lesions in this area become a reasonable alternative for patients with these tumors. 14 The most appropriate and safest surgical approach to lesions of the anterior and lateral skull base can be devised only with accurate and precise preoperative assessment. Even with the advent of new diagnostic techniques, the complex nature of the surrounding anatomy, when pathologically altered or changed by prior surgery, is such that the surgeon occasionally finds relationships of tumor to vital structures that were not anticipated. This problem ultimately is demonstrated by the fact that occasionally a major surgical procedure is performed only to realize that the tumor cannot be completely resected. Traditional approaches to the skull base required widened exposure and peripheral control of vascular structures leading to disfiguring and morbid results directly imposed by the surgical approach itself, and not necessarily from tumor extirpation. The literature demonstrates the constant evolution of and search for more efficient, less invasive, and safer surgical approaches to this region. 5,8,14,15,16,22,25 The preoperative evaluation of brain and skull base tumors requires multiple imaging modalities. Precise imaging of the cranial vault and skull base contents, as well as the tumor itself, is vital for the accurate diagnosis and treatment of such entities. Currently, MR imaging, CT scans, and angiography are used to plan various surgical trajectories, to define surgical anatomy, to analyze tumor volume, or to establish tumor burden. 18,24 Operatively, these images are used to provide step-wise comparisons of the surgical field, incision planning, and tumor margin definition. Postoperatively, these modalities are used to determine the extent of tumor resection, the degree of response to radiation therapy or chemotherapy, and in follow-up, to compare clinical condition and tumor burden for decisions regarding future care management. The development of a more exact three-dimensional, interactive anatomic "road map" for each specific patient's disease and anatomy will allow the skull base surgeon to achieve a more accurate preoperative assessment. This may lead to a less invasive and less morbid approach, and can allow development and refinement of new approaches without fear of actual morbidity and mortality. Additional benefits are apparent in that students of this type of surgery can study and obtain expertise of the anatomy of the cranial base in a nonthreatening, more interactive, and intuitive environment. It is conceivable that this method may be used to assist the patient to visualize and understand one's own disease process leading to a new standard of informed consent. To establish an accurate preoperative treatment plan, the cranial base surgeon would like to peer directly into the head of the patient to obtain a clear understanding of tumor margin and tumor burden. Today, with the advent of high performance computing hardware and complex algorithm development, such an intuitive and interactive system with real-time performance can be developed.