Objectives: The main objective of the present work was to identify, by means of intraoperative electrical stimulation, the supplementary motor area (SMA) region which is implicated in complex motor function. The functional prognostic relevance of the surgical preservation of this area was also analyzed.
Method: Fifteen patients with tumors infiltrating the premotor cortex were selected. All patients were operated under awake conditions. Primary motor cortex was identified with intraoperative electrical stimulation (IES). To identify the SMA, patients were asked to do a finger opposition motor task with their hand contralateral to the lesion, that was blocked by electrically stimulating the premotor cerebral cortex.
Results: SMA was identified in all patients with IES. Complete surgical resection was achieved in 13 patients (86.6%) and subtotal in 2 patients (13.3%). SMA function was preserved in 14 patients (93.3%). In only one patient the SMA was partially resected because of tumor infiltration (6.6%). In the immediate postoperative period, 8 patients (53.3%) did not show changes in comparison to their preoperative clinical status, and 2 patients improved. At 6 months follow up, 5 patients (33.3%) were asymptomatic and 10 patients showed permanent deficits. In this last group, five patients (33.3%) showed mild deficits that did not interfere with a normal life. In the other 5 patients (33.3%), permanent deficits interfered with daily life activities: two patients presented severe hemiparesis 3/5 (same similar to their preoperative status with no improvement), one patient had motor aphasia, and two other patients (13.3%) showed permanent left SMA syndrome. In two patients with severe postoperative hemiparesis, tumor infiltration of primary motor cortex and piramidal pathway was observed; severe preoperative motor deficit (KPS <70) was associated with poor functional outcome.
Conclusions: Intraoperative electrical cortical stimulation is useful to identify the SMA. Once identified, SMA preservation decreases the risk of postoperative symptoms and permanent SMA syndrome. When SMA is infiltrated by the tumor, radical resection may cause permanent neurological deficits, specially in the dominant hemisphere. Severe preoperative motor deficit was associated with poor outcome.