A New Biplane Neuroradiologic Localizing Instrument

Stereotactic or stereotropic surgery has been the accepted and established terminology for the neurosurgical therapeutic technic wherein a target area within the brain is localized for the precise placement of an electrode at this predetermined point. The terminology has been questioned frequently, but repeated use has resulted in its acceptance. Classically, the Horsley and Clarke apparatus (3) is recognized as the first piece of equipment fabricated for stereotactic surgery in animals, and Spiegel et al. first employed it in man (8). Its primary use is in the treatment of rigidity and tremors of Parkinson's disease or similar maladies. While there have been individual variations of the equipment for proper placement of electrodes within the brain, it has been generally believed that a precision of accuracy within 1 mm was greatly to be preferred to a nonselective free-hand technic of electrode placement. More recently, technics for percutaneous cordotomy and percutaneous copper electrocoagulation of intracranial vascular aneurysms have been developed (4–6), creating the necessity for more sophisticated instrumentation. A greater accuracy than 1 mm deviation from the point within the desired area is now required. The concept of stereotactic instrumentation has previously been based on calculations of three-dimensional planes. The development of the localizing instrument which is the subject of this report has made available the possibility of sighting the target point through the needle bore by means of an axial x-ray beam.2 The placement of the copper needles, which are 8 mil in diameter, within a vessel or aneurysm meant that an error of 1 mm (40/1000 in.) would result in a disaster. With the original concept of the target-point localization with an x-ray beam, the problem appeared that one would be producing a classic focal-spot camera which would result in the radiographic filming of the effective focal spot of the x-ray tube (2). This would be of no value in sighting the cylinder of a needle toward the target point. After we made preliminary observations with the fluoroscope, it became apparent that the cylinder of a needle could be identified and recorded. On review of the concept of a focal-spot camera, it became apparent that the camera was based upon a point-opening, whereas the instrument of our desired concept contained a cylinder within the x-ray beam. This latter acted as a miniature collimator and provided a path for the axial or parallel x-ray beam. The design of the localizing instrument has retained two concepts of the stereoencephalotome which include a fixed rigid position of the skull and the possibility for recording electromagnetic energy from the x-ray tube. The biplane “akidopeirastoscope” includes mounting of the x-ray tube and miniature collimated needle in a fixed relationship, with the needle being centered at the effective focal spot of the x-ray tube.