Abstracts

Rationale: Stereotactic electroencephalography (sEEG) provides recordings of deep brain activity that is used for the localization of epileptogenic tissue. Precise placement of electrodes is crucial to provide optimal coverage of the target tissue. Imprecision in the placement of these invasive devices can lead to inaccurate interpretation of the recordings, and place patients at risk for injury. Multiple factors are considered when planning stereotactic EEG, including the location of the target tissue, the patient's anatomy, the angle of approach, the skull thickness, and the depth of placement. This study was performed to evaluate the influence of the planned trajectory on the precision of electrode placement. Methods: Patients were selected from a retrospective cohort of 21 patients who underwent Phase II surgical evaluation. Of these, six patients had both (1) pre-operative plans available, and (2) post-operative imaging to confirm electrode placement. Surgery was performed by a single neurosurgeon using a frameless implantation technique using navigation software (Brainlab AG). Intraoperative CT and pre-operative MRI were merged to guide placement of a trajectory arm, through which intracerebral electrodes were placed. Among the six identified patients, 66 sEEG electrodes were placed. Four trajectories were excluded due to intraoperative adjustment to the trajectory, with the new trajectories not being available. The resulting 62 trajectories were evaluated using the navigation software. Precision was determined from the Euclidean distance between the target location and the electrode imaging artifact on CT or MRI. The angle of approach was approximated geometrically from 3-dimensional post-operative imaging. Results: The tip placement precision was measured to be 5.3 +- 2.2 mm (standard deviation). Angulation of approach ranged 0.4-45.4 degrees from skull surface normal. Electrode tip precision was higher with < 15 degree angles (4.5 +- 2.2 mm) when compared to 15-30 degree angles (5.8 +- 1.8 mm; p-value 0.017 using 2-sided Student t-test). Precision of skull entry was also higher with < 15 degree angles (1.4 +- 0.9 versus 2.5 +- 1.6 mm; p-value 0.0067). Pearson Correlation between precision and implantation depth (electrode tip to cortex) was statistically significant (0.34; p-value 0.0068), with higher precision seen with shorter planned trajectories. Conclusions: Higher precision of frameless stereo EEG electrode placement is seen with trajectories designed with (1) shorter trajectories, and (2) a nearly perpendicular approach. This finding may help guide clinicians understand tradeoffs in electrode trajectories, and to develop successful frameless stereo-EEG surgical plans. Funding: No funding