Intraoperative electrocorticography and cortical stimulation in children.

Intraoperative electrocorticography has been used in the surgical management of children with medically refractory epilepsy to localize anatomic areas of focal seizure onset, guide the extent, and completeness of resective epilepsy surgery, aid in functional mapping of cortical anatomy, and predict epilepsy surgical outcome. Evidence to support its utility for these purposes is somewhat controversial, particularly in children where the literature is substantially lacking. Usefulness is often dependent on the underlying pathology, and type of resective surgery. It seems to be valuable in the following circumstances: (1) tailoring the extent of hippocampal resection during temporal lobectomies, (2) guiding resection of cortical brain malformations, low-grade tumors, and other neocortical lesions, especially those involving eloquent cortex, and (3) monitoring for afterdischarges during functional cortical mapping. Most literature on this topic is not purely pediatric, and in most circumstances, is the result of combination of both children and adults cases. Cortical stimulation has been shown to be a useful, reliable and safe technique to assess motor, sensory, and speech function in children. As compared with adults, children manifest the following: (1) they need higher Amperage thresholds to elicit responses. In children younger than 10 years, cortical stimulation identifies language cortex at a lower rate than in children older than 10 years or in adults. (2) They have variability within the same individual in the stimulation threshold depending on the cortical site. This often results in the need to maximize stimulation of currents at each cortical site regardless of adjacent afterdischarge threshold. (3) They demonstrate more difficultly to evoke motor responses particularly with certain pathologies such as retrorolandic low-grade tumors. Often also the effective current intensity decreases after lesion removal. As a consequence of the above, the pulse width used for cortical stimulation in children often varies between 0.14 and 200 ms, the frequency ranges between 20 and 50 Hz, the current intensity between 0.5 and 20 mA, and the train between 3 and 25 seconds. Cortical stimulation can identify cortex with reorganized function secondary to congenital lesions and cerebral plasticity. These lesions include brain tumors, cortical dysplasia resulting in intractable epilepsy, and cavernous angioma causing epilepsy. When compared with other presurgical tests, cortical stimulation was shown to have results consistent with those of functional magnetic resonance imaging and Wada testing. It has the disadvantage of being invasive but the advantage of being highly accurate allowing for surgical tailored resections. Although the evidence for the utility of electrocorticography and cortical stimulation is exclusively level IV evidence, it is unlikely that randomized studies are going to be performed due to practical, ethical, and other reasons. The weight of the uncontrolled data at this stage is such that in children electrocorticography remains to be a useful test in some cases of cortical resection and that cortical stimulation is usually indicated when resection in or near eloquent cortex is needed.