SISCOS in focal cortical dysplasia: localization and comparative analysis with MRI

This study evaluates the efficacy of SISCOS (Subtraction ictal-interictal SPECT coregistered to SPECT) in localizing the epileptogenic zone (EZ) in focal cortical dysplasia (FCD), comparing its predictive performance with MRI and post-surgical outcomes based on ILAE classification.

84 patients with drug refractory epilepsy (DRE) who were operated and had histopathology consistent with FCD, were included in the study. All patients had undergone a complete work-up including SISCOS and MRI for EZ localization, followed by discussion in the multidisciplinary epilepsy surgery meeting prior to surgery. Ictal & interictal perfusion SPECT studies were performed with Tc-99 m Ethylene Cysteinate Dimer (Tc-99 m ECD) followed by SISCOS analysis using SPM2 and Bioimage Suite 2.6. Concordance for localization was determined by comparing with the surgical resection site and post-surgical outcomes were assessed using the ILAE classification.

The concordance for EZ localization demonstrated by SISCOS was 73.8% and MRI was 82.1%. 52 patients (61.9%) had good surgical outcome and 31(59%) of these were FCD type 2. In patients with discordant MRI findings, SISCOS was able to provide localisation in 86% (13/15), with 69.2% showing good surgical outcomes. Sensitivity of SISCOS and MRI was 73% (95% CI = 59-84.8%) and 78% (95% CI = 67.5-90.3%) respectively with no significant difference between the two. In FCD type I, both SISCOS and MRI revealed a similar a sensitivity of 76.4% (95%CI = 50.1-93.2%). Concordant cases exhibited higher seizure-free odds ratios for both modalities.

SISCOS is effective in localizing the EZ in FCD patients, comparable to MRI. Integrating SISCOS and MRI enhances lesion detection, especially in MRI discordant cases. A comprehensive diagnostic approach utilizing SISCOS and MRI can optimize the non-invasive pre-surgical assessment in DRE thereby guiding surgical decision-making in a resource-limited setting.