Stereotactic Principles

Abstract

Development of stereotactic principles in neurosurgery wouldn’t have been possible if the brain wasn’t soft in consistency and easy to penetrate— with the exclusion of vessels and meninges—without serious dysfunctions developing. Nevertheless many neurologists think puncture is hazardous and forget the ample evidence, derived from numerous stereotactic interventions, that puncture with guided (instead of free-hand) instruments of small diameter (preferably less than 4 mm) and with a blunt tip eliminates any real danger. The author has punctured once in case of emergency with a blunt, guided, 2 mm needle through the mesencephalon, pons and medulla to reach an intramedullary hematoma; after the evacuation functions restored and the patient recovered without any vital dysfunction. On the other hand, stereotactic techniques could only be developed due to the fact that the skull forms a firm envelope for its contents. The bone of the skull I convexity provides the foundation for any stereotactic equipment and makes it possible to construct an apparatus that can be fixed to the skull with screws. This enables the neurosurgeon to introduce any stereotactic instrument that is supported by a bar, which is connected to the apparatus, just by shding the guided instrument (needle, forceps, electrode) slowly through a burrhole into the brain. Penetration of surrounding brain structures by this guided technique is made even less dangerous by the high number of degrees of freedom that a modern apparatus possesses. So, after calculations have been made and the coordinates estabhshed, the instrument bar is adjusted in such a way that the tract towards the target is the preferable one (the shortest or the safest) according to the surgeon’s opinion.