gms | German Medical Science

Objective: In cases of surgery close to eloquent areas measurement of functional activity is essential to avoid postoperative dysfunction. We measured the activity of speech related cortical areas preoperatively with two modalities, MEG and fMRI, to be able to eliminate errors of each modality and to increase pertinent information and reliability.

Methods: MEG measurements were carried out with a 2 x 37 channel biomagnetic system (Magnes II, 4-D Neuroimaging). Localization was performed by 1-dipole fit or beamformer analysis. For fMRI we used a 1.5T MR scanner with echo planar imaging (Sonata, Siemens Medical Solutions) and a block paradigm with 180 measurements in 6 blocks (rest alternating with activation, 25 slices, 3mm thickness & resolution TR=2470, TE=60). 90 patients were examined. We used a silent naming task where the patient had to attribute visually presented drawings and a silent reading task in which we presented monosyllabic words which had to be read silently. A third paradigm consisted of reading numbers which had to be added. Further experiments consisted in building a sentence from presented nouns (verbal generation task) and answering to displayed questions.

Results: MEG and fMRI results were in agreement in most cases. However, in 50% of patients with high grade glioma, the language area abutting the tumor did not show clear BOLD activation in fMRI. We observed Wernicke activity in the planum temporale and the supratemporal sulcus. Broca activity was found at the bottom and top of the inferior frontal gyrus pars opercularis and the frontal top of the insula. There was also activity in the precentral sulcus. In all patients, who underwent surgery, there was no permanent worsening of functional abilities as compared with the state it was before surgery. Only 3 patients experienced a slight transient language difficulty lasting from 1 to 8 days. One patient we observed, exhibited a shift of the cortical language representation from the left to the right hemisphere.

Conclusions: Measuring both fMRI and MEG provides a higher degree of reliability in presurgical brain mapping, thus expanding the spectrum of surgically accessible lesions.