Stimulation mapping via implanted grid electrodes prior to surgery for gliomas in highly eloquent cortex

To evaluate whether preoperative mapping of higher cortical functions with subdural grid electrodes can help to maximize resection in functional areas and avoid permanent injury.

A consecutive series of 16 patients (female: n = 7, male: n = 9, mean age of 38 yr) with a history of seizures and without focal deficit was reviewed, harboring gliomas located in the dominant hemisphere adjacent to or in the F3 gyrus/Broca area (n = 11), parietal/perisylvian area (n = 5) and additionally the pre- or postcentral area (n = 15). All patients in this series were operated for cytoreductive purposes only and not for treatment of intractable seizures. To preoperatively define and intraoperatively tailor the extent of resection all patients had a presurgical grid implantation for functional brain mapping.

No permanent morbidity/mortality was observed after grid implantation and resective surgery. On postoperative MRI the resection was complete (100%), nearly complete (>90%) in n = 9 and subtotal (60% to <90%) in n = 5 cases. Twice, only biopsies were taken according to the results of mapping. All patients with high-grade gliomas had adjuvant treatment with radiation and chemotherapy. After a mean follow up of 20.4 months, no tumor relapse or growth was seen in all cases of resection.

Preoperative grid mapping is a safe and precise instrument to evaluate language and/or associated left perisylvian functions in patients with gliomas. It may be considered a valid alternative to awake craniotomy to maximize safe resection.