Discrepancy between preoperative noninvasive evaluation and intraoperative electrical cortical stimulation for motor...

Evaluating residual motor function and functional compensation is essential before performing hemispherotomy. We have been evaluating hand motor function using transcranial magnetic stimulation (TMS), which cannot confirm the lower limb functions.

A male teenager with a huge arachnoid cyst in the right frontotemporal region and extensive polymicrogyria and gyral dysplasia in the adjacent lobes experienced focal to bilateral tonic-clonic seizures. We performed functional magnetic resonance imaging (MRI) and electrical cortical stimulation in addition to TMS. Functional MRI and TMS-motor-evoked potential (MEP) results suggested that the left primary motor cortex elicited the bilateral motor response, while intraoperative cortical stimulation MEPs revealed that the primary motor areas of each lower limb were controlled contralaterally. Consequently, we performed a total callosotomy instead of a hemispherotomy.

The results suggest that a preoperative diagnosis of complete hemispheric damage based on noninvasive examinations is not sufficient in some cases to determine the operative strategy. A combination of pre- and intraoperative examinations may be required to prevent unexpected neurological complications.