General Medical Information

Computer-Assisted Surgery

Barbara A. Zeifer

The advent of the helical, or spiral, CT has enabled scanning of broad anatomic areas in a relatively short time with low radiation exposure. Helical CT is essentially one continuous scan in which block or volume of information is acquired that can be manipulated later in many different ways. One such reformation of these data is to slice into the volume and produce a two-dimensional image in an anatomic plane other than the scan plane. Computer-assisted surgery takes advantage of this technology and adds to it three-dimensional spatial localization. The patient undergoes helical CT of the entire midface in the axial plane with either a headset or fiducial markers in place, depending on the type of equipment. The data are transferred to the computer in the operating room. At surgery, the data set in the computer is matched or referenced to the patient with the headset or the markers so that a probe placed into the sinonasal cavity is located accurately in space and then indicated on the screen. The computer screen shows the axial, sagittal, and coronal CT sections, the intersection of which corresponds to the tip of the probe. Depth and precise location of instruments can be checked during the surgical procedure. This technique is particularly useful in revision surgery and management of severe polyposis, in which anatomic landmarks are limited.