Misleading EEG Lateralization Associated With Midline Shift.

Midline discharges, lateralized periodic discharges, and seizures have been described with ipsilateral lesions that result in midline shift (MLS). Periodic discharges and seizures arising contralateral to a known lesion have not previously been described as a sign of MLS. We present four patients with focal brain lesions, resulting in MLS and epileptiform discharges arising from the contralateral hemisphere. Patient 1 underwent a right anterior temporal lobectomy. On postoperative day 2, computed tomography demonstrated a right to left MLS of 12 mm, and EEG was remarkable for left temporal nonconvulsive status epilepticus. Patient 2 experienced a subarachnoid hemorrhage, which was more prominent on the left. Computed tomography after craniotomy demonstrated left to right MLS of 6 mm, and EEG was remarkable for right lateralized periodic discharges. Patient 3 had a right subdural hematoma and underwent craniotomy for evacuation. On postoperative day 3, computed tomography demonstrated a right MLS of 7 mm, and EEG was remarkable for left temporal nonconvulsive status epilepticus. Patient 4 had traumatic brain hemorrhages with maximal left frontotemporal involvement. Six days after the trauma, computed tomography was significant for left to right MLS of 9 mm, and EEG showed right lateralized periodic discharges. Epileptiform discharges and seizures occurring contralateral to a known lesion may be an indicator of MLS.