Date of download: 6/23/2016 Copyright © 2016 McGraw-Hill Education. All rights reserved. Supplementary Sensorimotor Area (SSMA) Seizure; Subdural vs Scalp EEG Recording. A 14-year-old boy with frontal lobe epilepsy caused by an extensive malformation of cortical development (MCD) in the right frontal region who underwent invasive EEG monitoring. Subdural EEG during his typical simple partial seizure described as mild stiffening of the left arm with or without head turning to the left shows diffuse fast activity maximum in the mesial frontal electrodes (MIH and AIH) (open arrow) with some spreading to the lateral frontal region (LF electrodes in the box). Ictal tachycardia (double arrows) is observed at the onset of seizure. Note the similarity between the subdural and scalp EEG recordings in clinical features, and in EEG and ECG findings. The major difference between the subdural and scalp EEG recordings is the amplitude, which is lower in the scalp EEG recording due to volume conduction. The EEG pattern is consistent with asymmetric “paroxysmal fast activity (PFA).” Axial FLAIR MRI demonstrates a lipoma in the right sylvian fissure (arrow) and extensive polymicrogyria (PMG) in the entire right frontal lobe (open arrow). The patient has been seizure free since the surgery. All patients with SSMA seizures had preservation of consciousness during the seizure unless secondarily generalization occurred. Tonic posturing of the extremities was present in all patients, and in 63% it was present bilaterally. Adversive movements were not seen unless the seizure became secondarily generalized. Interictal and/or ictal abnormalities were present at or adjacent to the midline in almost all patients. 40 In patients whose seizures began in the medial frontal region (anterior cingulate, supplementary motor region, medial perirolandic region), ictal patterns were significantly shorter than those of other groups and included, no rhythmic electrographic changes were seen, and rhythmic electrographic changes occurred after the onset of clinical seizures or generalized suppression or PFA. This is probably because the primary seizure generator is located some distance from the scalp electrodes and requires a greater amount of cortical involvement (implying propagation) before electrographic activity can be detected. In contrast, patients whose seizures were of dorsolateral origin had a high percentage (68%) of focal electrographic seizure activity (rhythmic fast activity, alpha or beta activity, or repetitive spikes) that preceded the onset of clinical symptoms and was thus distinguished from seizures that originated in the medial frontal region. 41,257 The absence of focal electrographic seizure activity nearly excluded the possibility of seizures emanating from the dorsolateral frontal region. 257 PFA may be a reflection of proximity of the epileptogenic zone to the recording electrodes. Seizures arising from the lateral frontal convexity began with repetitive epileptiform activity, whereas seizures of patients with mesial lesions more often began with rhythmic theta activity. PFA was observed at the onset of seizures arising from the inferior aspect of the supplementary sensorimotor area and cingulate gyrus, where the distance between the nearest scalp electrode and the generator is great. PFA was virtually never observed at the onset or during the course of MTLE seizures. Therefore, PFA is generated during neocortical ictal activation. 41,258– 260 Its presence is not primarily dependent on the proximity of the recording electrode to the epileptic generator. Rather, the presence of paroxysmal fast activity may be an expression of propagation from the epileptogenic zone to areas underlying the involved scalp electrodes, or may be influenced by other factors such as a pathologic substrate. 41 Incomplete removal of epileptic activity as defined by subdural EEG is likely to result in seizure recurrence. 261,262 Interictal and ictal paroxysmal fast activity is reported to be more specific for FCD than other pathologies. 263–265 The localized burst, continuous, or nearly continuous pattern of epileptiform discharges on ECoG was associated with the FCD lesion. 73 Interictal PFA and runs of repetitive spikes correlated with the ictal onset zone, whereas isolated spikes did not, and incomplete resection of interictal PFA correlated with seizure recurrence. 261 Legend : From: Focal Epilepsy Atlas of Pediatric EEG, 2011 From: Focal Epilepsy Atlas of Pediatric EEG, 2011