Abstracts

Frameless image-guidance techniques for implantation of depth electrodes for intracranial monitoring are increasingly used, but few reports have assessed the accuracy and precision of these techniques., Frameless image-guidance using the Stealth[reg] (Medtronic) neuronavigational hardware and Cranial[reg] software was used exclusively for the implantation of depth electrodes since 1998. Electrodes were implanted through burr holes using an orthogonal (trans-temporal) approach (N=32 patients), typically into the amygdala and 2 - 3 electrodes in the hippocampus or parahippocampal gyrus on each side, or occipital approach (N=3 patients). We analyzed the implantation of all electrodes for which the intra-operative planning trajectories (saved on the pre-operative MRI scan by the Stealth) and post-operative MR imaging were available (N=155 electrodes: 150 orthogonal, 5 occipital). The pre- and post-operative image sets were registered using the navigational software, and a vector was constructed from the [quot]intended[quot] target to the [quot]actual[quot] location of the electrode tip (taking into account imaging artifact around the electrode)., The discrepancy between the [quot]intended[quot] and [quot]actual[quot] location of the orthogonal electrode tips was 5.6 +/- 2.9 mm. There was no significant difference between accuracy of electrodes implanted on the first vs. second side as might be expected from brain shift, nor on the left (n=80) vs. right (n=70) side. The direction of error could be characterized as [quot]too deep[quot] for 93 electrodes as opposed to [quot]too shallow[quot] for 50 electrodes probably due to difficulty in securing the electrode precisely during placement. Five electrodes implanted via an occipital approach had an error of 7.7 +/- 8.0 mm, reflecting lower accuracy and greater variability likely due to the longer passage. No patients implanted via an orthogonal approach required reoperation in contrast to 1 of 3 patients implanted occipitally. No complications definitively related to post-operative MR imaging were detected over the 150 electrodes and 32 patients, although 2 patients recently implanted experienced transient neurologic deficits which in one patient may have been infectious in etiology but in the other was uncertain., Frameless image-guidance implantation of depth electrodes via an orthogonal approach is an effective technique with sufficient accuracy for intracranial monitoring.,