Abstracts

RATIONALE: Frameless image-guidance systems have become widely available to neurosurgeons over the past few years. Epilepsy surgeons have on the whole embraced this technology, but there remains some reticence with regard to accuracy for electrode placement when compared to frame stereotaxis. The level of intra-operative usefulness of image-guidance with regard to well-recognized anatomical structures has also been debated.
METHODS: In a series of 50 consecutive image-guided epilepsy surgery cases, we have analysed both accuracy and surgical utility. Cases included 7 frameless depth electrode placements. In these, true surgical accuracy was assessed by fusing post-implantation MRIs with pre-implantation studies with planned trajectories. The difference between planned trajectory and final electrode position was measured. Accuracy was also assessed in 32 non-lesional and 9 lesional epilepsy cases and in two functional hemispherectomies.
RESULTS: In 42 depth electrode placements, targeting accuracy was 2.2mm +/- 1.1mm. Temporal lobe cases included anterior temporal resections, selective mesial resections, subpial trans-sections and combined / hybrid procedures. Usefulness in the temporal lobe was mainly 1) in finding the temporal horn, 2) defining the supero-mesial extent of amygdalar resection and 3) confirming the posterior extent of hippocampal resection. To optimize accuracy in the amygdala, we recommend that this area be addressed prior to opening the temporal horn of the ventricle, especially in patients with significant atrophy. In functional hemispherectomies, guidance for disconnective incisions was extremely useful. The most obvious application was for lesion resection. Usually lesions presenting with epilepsy are non-enhancing. In this context, image-fusion of FLAIR MRI sequences was paramount. Fusion of functional images was occasionally performed.
CONCLUSIONS: The spectrum of applications of image-guidance in epilepsy surgery has been reviewed and future perspectives will be discussed.