FRAMELESS STEREOTAXY FOR SURGERY OF THE EPILEPSIES - PRELIMINARY EXPERIENCE - TECHNICAL NOTE

Frameless stereotactic techniques used in conjunction with three-dimen sional images allow accurate planning and performance of a variety of neurosurgical procedures. The authors have used the frameless stereota ctic Allegro Viewing Wand system to provide real-time correlation of t he operating field and computerized images in 42 neurosurgical operati ons, including 31 epilepsy procedures. The system consists of an image -processing computer that creates three-dimensional and triplanar imag es; a mobile computer to display reformatted magnetic resonance images ; and a hand-guided, articulated, position-sensing arm with a probe. A t the start of the operation, the probe identifies the patient's facia l and scalp features and correlates these with the computerized images . The position-sensing arm can then guide the operation and locate ana tomical structures and lesions of interest. This system can be used to advantage in performing smaller craniotomies and intraoperatively loc ating anatomical structures and lesions to be removed. Postoperative m agnetic resonance images demonstrate that this technique was accurate to within 3 mm in measuring the anteroposterior resection of fixed str uctures, such as hippocampus and corpus callosum. Disadvantages includ e longer preoperative preparation for data analysis and lack of both r eal-time computer analysis of tissue removal and angiographic data dis play. Preliminary experience suggests that the viewing wand system's a dvantages outweigh the disadvantages, and it is most helpful as an adj unctive navigational device in the microsurgical treatment of epilepsy .