A microstereotactic approach to small CNS lesions. Part I. Development of CT localization and 3-D reconstruction techniques.

The authors describe a newly designed and utilized stereotactic methodology for the removal of central nervous system lesions as small as a few millimeters in diameter. These small lesions are detected and localized by non-invasive computerized axial tomography (GE 8800 scanner) with additional computer processing of the digital data by means of a PDP-1145 computer. Multiple computer algorithms have been developed to enhance regions of interest on CT scans by three-dimensional reconstruction and magnification techniques. This same data can then be used to calculate a stereotactic approach to a small CNS lesion. The stereotactic approach coordinates are then mated to a head fixation system modified from the Reichert-Mundinger stereotactic apparatus enabling information transfer from CT scan to the stereotactic surgical system. These small CNS lesions, as small as 5 mm, can be removed with the apparatus described herein under direct binocular 3-D vision with minimal tissue damage, through a small trephine craniotomy or burr hole. Newly designed instruments and instruments in the process of being developed are mounted on a micromanipulator attached to the Riecher-Mundinger frame for guidance at surgery. These new instruments include stereoendoscopes with xenon arc illumination, multiple tissue expanders for exposing the operative site, a radiation tracer probe, a rotary-sucker extractor, and multiple other small instruments for operating and removal of blood and tissue from small CNS lesions. The stereotactic frame accurately defines all areas of the cranium in three-dimensional coordinates, and its combination with the micromanipulator-instrument assembly enables the site of any small CNS lesion, the three-dimensional coordinates of which have been located by additional computer processing of the CT digital data, to be accurately approached by the stereotactic guide micromanipulator assembly. The instrument described herein allows removal of very small tumor burdens, and opens the possibility for successful secondary application of adjuvant immunotherapy to a CNS tumor site as described in part II of this paper.