Intraoperative brain mapping to identify corticospinal projections during resective epilepsy surgery in children with congenital hemiparesis

The purpose of the study is to determine corticospinal organization using intraoperative neurophysiologic monitoring (IONM) during resective epilepsy surgery for patients with congenital hemiparesis and intractable epilepsy.Ten patients, aged 3-17, with intractable epilepsy underwent resective surgery. Transcranial stimulation (TCS) was achieved using a pair of cork screws at Cz and C3/C4, respectively. A 1 × 4 stimulating electrode strip was placed on the presumed motor cortex of the affected hemisphere for direct cortical stimulation (DCS) after craniotomy. Multipulse TCS and DCS train stimulation was delivered, with simultaneous recordings from bilateral abductor pollicis brevis and abductor halluces, to determine the corticospinal projection pattern of the paretic limbs.The above mapping techniques revealed ipsilateral corticospinal projections from the contralesional hemisphere to target muscles in the paretic limbs in three patients, projections from both hemispheres to target muscles in three, and preserved crossed projections from the affected hemisphere in four. Nine patients were seizure free after surgery. Five had unchanged postoperative functional status, and three showed minimally improved use of the paretic hand. Two developed new motor deficits after surgery, which may have been due to a premotor syndrome in one patient, since it completely resolved within 2 weeks. The other experienced increased weakness of the paretic lower limb because a small part of the eloquent cortex was removed for better seizure control.Using IONM to define the corticospinal projection pattern is a valuable technique that can potentially replace preoperative fMRI and transcranial magnetic stimulation in resective epilepsy surgery, particularly for younger patients.