Functional magnetic resonance imaging localization of ictal onset to a dysplastic cleft with simultaneous sensorimotor mapping: intraoperative electrophysiological confirmation and postoperative follow-up: technical note

Although technically challenging to obtain, ictal functional magnetic resonance imaging has been used to localize ictal onset zones in a small number of patients. We used this technique to demonstrate the inherent epileptogenicity of dysplastic cortex. We present a 16-year-old female patient with intractable left-sided sensorimotor seizures and a congenital dysplastic cleft lying along the right rolandic fissure. Preoperative functional magnetic resonance imaging (blood oxygen level-dependent sequence, 1.5 T) localized the motor and sensory cortices to the anterior border of the cleft. During a speech activation run, the patient experienced a 20-second seizure. Initial activation was seen within the dysplastic cortex along the deep posterior margin of the cleft. Intraoperative median nerve stimulation produced a distinct N20/P20 wave inversion over the dysplastic cleft. Stimulation mapping performed with the patient awake confirmed the location of the sensorimotor cortex on the anterior border of the cleft, and preresection electrocorticography identified abundant interictal spikes along the posterior border after opening the cleft. After surgical resection of the dysplastic cortex, the patient exhibited transient minimal weakness and mild neglect, which resolved within 1 week. Two years after surgery, she was neurologically intact and seizure-free. This study used functional magnetic resonance imaging to demonstrate the inherent epileptogenicity of dysplastic cortex and to simultaneously map ictal and functional cortex. The N20 wave inversion can be a useful intraoperative tool for identifying the central sulcus (or its equivalent), even in the presence of abnormal cortical architecture.