[Computer-assisted surgery of the paranasal sinuses with an opto-electronic stereotaxic system]

A basic problem common to all systems for computer-assisted surgery (CAS) is the exact registration and referencing, that is, the transfer of preoperative image data to the intraoperative pathology. A system for computer-assisted ENT surgery should provide high precision as well as noninvasive registration and referencing. We present a system designed for such use in paranasal sinus surgery that is based on optical digitizing with several custom-made self-localizing surgical instruments.

The system tracks the correct alignment of the head during CT data acquisition and continuously throughout surgery. A transformation matrix and a plane equation of the CT scan are used to match points of the object space to the image space detecting fiducial markers on the CT scans by an automatic algorithm. For position measurements a special reference frame and surgical instruments were developed and equipped with infrared light-emitting diodes that could be detected in real time. Measurements for repositioning of the reference system in a model and during real operations demonstrated a mean error ranging from 0.69 to 1.01 mm and from 0.76 to 1.67 mm respectively. Clinical experience with the application of the system for 15 patients who underwent surgery for different paranasal sinus pathologies is reported.

Results suggest that the non-invasive reference system and the locatable surgical tools may be effective, accurate and useful for computer-assisted identification of intranasal structures. Such systems may contribute to further improvement of minimal invasive intranasal sinus surgery.