Abstracts

Rationale: The gold-standard method of determining cortical functional organization in the context of neurosurgical intervention is electrical cortical stimulation (ECS), which disrupts normal cortical function to evoke movement. This technique is imprecise, as motor responses are not limited to the precentral gyrus but are found up to 4 cm anterior or 2 cm posterior to the central sulcus. ECS also can trigger seizures. It is not always tolerated, nor always successful, especially in children. In contrast to ECS, endogenous motor and sensory signals can be mapped by somatosensory-evoked potentials (SSEP), functional magnetic resonance imaging (fMRI), and electrocorticography of high gamma signal power (hgECoG), which reflect normal cortical function. SSEPs evaluate physiologic response to peripheral nerve stimulation. Blood oxygen levels are compared between task and non-task in fMRI. Changes in power in high gamma activity on ECoG during hand movement rapidly localize cortical hand area. We compared these 4 modalities of mapping sensorimotor function in children.Methods: We retrospectively examined charts of all epilepsy surgery patients at Seattle Children s Hospital 6/20/99-6/1/11. Inclusion criteria were patients in whom we localized primary motor or somatosensory cortex via >2 of ECS, SSEP, fMRI, or hgECoG. We placed peri-Rolandic subdural electrodes to localize seizure onset. ECS was performed with an Ojemann stimulator, delivering up to 12 mA of current to electrode pairs and patients were monitored for motor activity. Median nerve SSEPs were inspected for a phase reversal of the N20 between adjacent electrodes. Functional imaging was performed on 1.5 or 3-Tesla scanners. Patients tapped their fingers for 39 seconds and then rested for 39 seconds. Children too young to cooperate were sedated and had passive movement to activate sensorimotor cortex. Post-acquisition t-test for each voxel between the 2 tasks were projected onto source images for analysis. We recorded hgECoG sampling at 1-2 kHz and band-pass filtered from 0.15 to 500 Hz during a 15 sec period of active or passive hand movement compared to 15 sec of restResults: Inclusion criteria were met by 48 patients. Average age at operation was 10.4 yo (range 0.7-18.8 yo), 44% were female. Operations were on the left hemisphere in 52%. Our youngest hgECoG mapping patient was 2 yr 10 mo, younger than any patient reported in the literature. There were lesions on neuroimaging in 35 (73%) children. Success rates of the 4 modalities and comparison to ECS are listed in table 1.Conclusions: ECS, SSEP, fMRI and hgECoG generally produced convergent localization of motor and sensory function. The success rate for hgECoG localizing sensorimotor cortex in children was the best, is quickest, the safest and does not require cooperation. The hgECoG maps in pediatric patients are similar to the 10 adult patients published in the literature. hgECoG and fMRI can be performed in children less than 3 years old to map cortical function. Although these initial results represent a small number of patients, they are encouraging and further studies are needed.