Frameless stereotactic endoscope-assisted transoccipital hippocampal depth electrode placement: cadaveric demonstration of a new approach.

PURPOSE: Hippocampal recording using depth electrodes is indicated in a small subgroup of patients with medically intractable seizures. There are several conventional techniques for implantation of hippocampal depth electrodes. We describe a new method for hippocampal depth electrode placement using an image-guided endoscopic transoccipital route. This technique is simple and effective, eliminating several drawbacks of conventional techniques.
METHODS: One silicone-injected cadaver head was used. A rigid endoscope sheath was inserted through a transoccipital corridor into the atrium of the lateral ventricle and then advanced to the temporal horn. Each of the hemispheres was cannulated. The hippocampus was identified visually, and a depth electrode was inserted into the substance of the hippocampus along its long axis under direct vision.
RESULTS: In both hemispheres we were able to successfully implant the depth electrode within the hippocampus. The advantages of our technique over conventional approaches are (1) there is no need for frame-based stereotaxy, thus reducing operating time and patient discomfort, (2) the electrodes are inserted into the hippocampus under direct endoscopic visualization, reducing the chance of injury to vascular structures, (3) there is no need to insert a larger cannula into the hippocampus before placement of the electrodes, reducing trauma to the hippocampus, and (4) the number of electrodes within the hippocampus can be assessed at the end of the procedure, reducing malposition.
CONCLUSION: We believe that image-guided endoscopic transoccipital hippocampal depth electrode placement can be performed with precision equal or superior to conventional techniques but without their major disadvantages.