An improved stereotactic technique for cyst cannulation

Stereotactic techniques for cannulation of cystic structures, within the brain, are well known. Superimposed structures (vessels, ventricles, etc.) may make this problematic as does the need to approach the cystic structure perpendicular to its tangent plane (rather than "glancing") as with a craniopharyngioma cyst. To facilitate a three-dimensional visualization of the trajectory, we have employed digital holography. Transparent holographic images of cystic structures, ventricles, and sulci are rendered from T2-weighted MR data. Holographic images of vascular structures are rendered from CT or MR angiographic data. Vascular holograms are superimposed over the brain holograms, demonstrating the spatial relationships of these structures with regard to each other. Holographic images of the skull are rendered from CT slices. A Laitinen stereotactic frame (Sandstrom) is placed on the patient prior to obtaining the CT. The skull, pre-existing shunt catheters, and the stereotactic frame are all readily visible. The brain and vascular holograms are superimposed on these. The resulting image clearly demonstrates cystic structures, ventricles, vessels, pre-existing catheters, all within the skull and stereotactic frame. Using this holographic image as a "phantom", the actual Laitinen stereotactic frame is placed within its holographic image. The optical trajectory is then chosen, and the articulated arm of the stereotactic device is so adjusted. Subsequently, the frame is used to effect stereotactic placement of the cannula, in the usual manner. The major advantages of this technique are twofold. The first advantage lies with the fact that the surgeon can readily visualize the entire trajectory of the needle, and easily appreciate all structures which may be encountered by the needle on its passage from the skull to the target. Presumably, the surgeon's knowledge of anatomy would unable such knowledge to be apparent, but in complex cases the "safe" corridor may be rather small, and its limits may not be intuitively obvious. This is all the more the case, when obstacles along the pathway are pathologically distorted, or when they are not of tissue origin (shunt catheters, etc.). Employing this technique, we have successfully cannulated cystic structures in six patients, three of which presented with complex trajectory problems.