Abstracts

Rationale: Detection of Focal cortical dysplasia at the bottom of sulcus (BOSD) is challenging. Dynamic statistical parametric mapping (dSPM) overlays spatiotemporal distribution of spike sources onto inflated brain model which has potential to provide better visualization of epileptic activity in sulci. Although the dSPM is able to demonstrate movie of spike activity, the pinpoint location of the BOSD is veiled in the dynamics of spike activities. We developed Advanced dSPM (AdSPM) to improve localization of epileptic zone of BOSD. We hypothesize that AdSPM pinpoints epileptic zone of BOSD.Methods: We analyzed 10 patients with intractable focal epilepsy who underwent epilepsy surgery with pathological confirmation of FCD type II. Six patients had BOSD and four patients had FCD at convexity. We compared spatial congruence between FCD and location of 1) MEG cluster of single moving dipole (SMD), and 2) spike volume in AdSPM. We defined spatial congruence between MEG cluster and FCD as hitting the location of FCD. In AdSPM, we investigated location of the highest spike volume from summation of Z score from each spike activation between ± 50msec. We adjusted threshold to the highest point where a single, contiguous patches of spike volume was observed. These patches were defined as the location of the highest spike volume in AdSPM.Results: In BOSD, SMD cluster hit BOSD in 4 patients and missed in 2 patients. The spatial relation of SMD cluster extended maximum 3 gyri from BOSD. AdSPM hit BOSD in 5 patients. In the other 1 patient, AdSPM mislocated the spike volume in the left superior temporal gyrus beside the inferior frontal BOSD. We performed lesionectomy plus 4-100% (mean, 68%) resection of SMD. Five patients with AdSPM in BOSD underwent lesionectomy with the resection of the spike volume area. In the other one patient, the temporal lobe AdSPM spike volume was left. All 6 patients with BOSD became seizure free with mean follow-up period of 13 months. In FCD at convexity, SMD hit FCD in all 4 patients. The clustered SMD fully covered FCD in 2 patients and partially overlapped in 2 patients. The spatial relation of SMD cluster extended maximum 3 gyri from FCD. AdSPM located the spike volume within FCD at convexity in all 4 patients. We performed lesionectomy plus 23-99% (mean, 69%) resection of SMD in 4 patients. All 4 AdSPM spike volume in FCD at convexity was resected. Three patients with FCD at convexity became seizure free and residual seizures in 1 patient with a mean follow-up period of 42 months.Conclusions: The extent of SMD cluster can cover the small epileptogenic BOSD, yet could not pinpoint the location of BOSD by including the other irritative zone. AdSPM can pinpoint the BOSD because of accumulating the spike activity using advanced statistical analysis. AdSPM may bring insight to the epileptic activity buried in BOSD.