Delayed onset of the supplementary motor area syndrome after surgical resection of the mesial frontal lobe: a time course study using intraoperative mapping in an awake patient.

Although the occurrence of the supplementary motor area (SMA) syndrome has been extensively reported following mesial lobe surgery, to our knowledge the time course of disease onset was never accurately documented. We describe a patient without deficit, despite harboring a glioma invading the left SMA. This patient was operated under local anesthesia, to perform intraoperative online sensorimotor and language mapping using electrical stimulations throughout the resection. No deficit was noted at the end of the tumor and SMA removal. The patient was maintained awake to perform an immediate control MRI. Aphasia and right hemiplegia occurred 30 min after the SMA resection. Total recovery was observed within 2 months. This work shows that the SMA syndrome may not occur immediately after SMA resection. We suggest that the transient compensation of the SMA function is likely due to residual activity of an oscillatory loop and/or short-term plasticity (rapid unmasking of parallel networks), with final recovery occurring due to long-term plasticity (neosynaptogenesis).