HELSINKI, Finland – Nov. 9, 2012 -- Patients with tumors in the perisylvian or opercular areas of the dominant hemisphere need to undergo awake surgery with language mapping in order to avoid loss of language abilities due to surgery. A reliable non-invasive presurgical language mapping technique would be of value to neurosurgeons because it would enable more targeted direct cortical stimulation (DCS). More targeted DCS could be of tremendous benefit to patients as it offers the potential for faster and safer awake surgery with smaller craniotomies.
In their paper Navigated transcranial magnetic stimulation for preoperative language mapping in a patient with a left frontoopercular glioblastoma, the authors Sollmann et al. describe the case of a left-handed patient with a left-sided glioblastoma within the opercular inferior frontal gyrus of the brain. Preoperative functional MRI (fMRI) indicated speech dominance of the right hemisphere and did not show any language-related activation in the left hemisphere. Language mapping was subsequently performed with an NBS System based on navigated TMS (nTMS). The NBS results showed a significantly higher rate of induced speech arrests for the left than for the right hemisphere, which very strongly suggested that the patient´s left hemisphere was, in fact, the speech dominant side. During awake surgery, intraoperative direct cortical stimulation indeed showed that speech impairment could be induced on the left side and confirmed the results from the NBS mapping. The contradicting results from the fMRI mapping technique were considered to have been impaired by anatomic and vascular changes due to growth of the tumor, and consequently unreliable for surgical planning. The authors suggest that nTMS offers promise as a replacement for fMRI and conclude that "This case suggests that nTMS may be useful for preoperative speech mapping in tumors."