Computer navigational microscope for minimally invasive neurosurgery.

Frameless navigational devices have recently undergone an evoluation to the point where they are being used more efficiently in the clinical setting. Most of the present-day systems utilize some form of mechanical arm to correlate registered points in space to the computer terminal. However, the articulated arm can be cumbersome and is an additional obstacle in the surgical field. To avoid this problem some groups have elected to transmit registered points and probe position using ultrasound or electromagnetic fields. However, in using magnetic fields, ferromagnetic metals can interfere with accuracy. On the other hand with ultrasonic digitizers accuracy is dependent on variable factors such as humidity, local temperature, and positioning of the emitters. In response to some of these difficulties inherent with frameless stereotaxy, the MKM system was developed. Essentially it is an optically based system in which the CT and/or MRI data are superimposed three-dimensionally onto the surgical field as seen through the microscope using head-up display technology. It requires no opto-kinetic link such as a headframe, mechanical arm, ultrasonic, and magnetic field. We have used the MKM microscope system to guide 18 neurosurgical procedures. This report illustrates the advantages of this system when combined with keyhole surgery to provide accurate excision of brain lesions while preserving normal tissue.