How small can the epileptogenic region be? A case in point

Objective: To present a case that demonstrates that seizures and interictal disturbances can be driven by a small area of functionally abnormal cortex. Methods: Two novel functional MRI network analysis methods were used to supplement conventional seizure and lesion localization methods: (1) regional homogeneity to quantify local connectivity, or synchrony, with a resolution of less than 1 cm(3) of cortex; and (2) small-worldness to combine information about whole brain network segregation and integration. Results: After a small corticectomy in the dominant supramarginal gyrus (13 X 7 X 6 mm) limited to the area of abnormal local connectivity, and smaller than the PET and SPECT abnormalities, the patient has been seizure-free for 3 years with no language deficit. Whole brain network characteristics normalized (small-worldness) to that of healthy controls. Conclusions: This case demonstrates that small areas of cortex may be highly epileptogenic, drive intractable epilepsy, and disrupt large-scale networks likely to be involved in core cognitive functions.