SEEG dynamic tractography-based spike source localization is useful across diverse brain regions and etiologies

To extend dynamic tractography-based spike source localization to stereoelectroencephalography (SEEG) and to test whether estimated spike sources (ESSs) and their resection relate to postoperative seizure outcomes across diverse epileptogenic regions and etiologies.

We studied 24 patients with drug-resistant focal epilepsy who underwent SEEG followed by focal resection or disconnection. For each patient, 100 interictal spikes were analyzed using Morlet wavelet time-frequency transformation (20-70 Hz). Electrode contacts showing significant broadband amplitude augmentation within 50 ms were defined as spike propagation sites. Diffusion MRI tractography generated streamlines from these sites according to observed propagation latencies. ESSs for each spike were defined as the centers of gravity of streamline endpoints. We defined the ESS resection ratio as the proportion of ESSs included within the resected or disconnected area on postoperative MRI and tested whether it was correlated with seizure outcome (ILAE class) and resection volume. Dynamic tractography visualized spike propagation from ESSs to propagation sites through white-matter pathways.

The median (IQR) ESS resection ratio was 75.0% (37.9-85.9). In unilateral cases (n = 18), a higher ESS resection ratio correlated with better outcomes (ρ = -0.51, p = 0.033), irrespective of resection volume. Dynamic tractography successfully visualized physiologically plausible spike propagation. Across 164 tracts, the median (IQR) propagation velocity was 0.99 mm/ms (0.49-1.46).

SEEG dynamic tractography enables localization of spike sources beyond the limits of electrode sampling and visualization of their propagation along white-matter pathways. The extent of ESS removal predicted favorable outcomes-particularly in unilateral cases-suggesting potential utility as a biomarker of the epileptogenic zone.