Abstracts

Presurgical evaluation of brain tumor patients is challenging, especially when the tumor is adjacent to eloquent cortex, such as language, somatosensory, and motor areas. Previously, functional mappping has relied on invasive methods, such as intraoperative cortical stimulation or stimulation via a grid implant. Neuroimaging methods have been used for presurgical evaluation in recent years, including functional MRI, PET, and magnetic sourse imaging (MSI). MSI has distinct advantages to the other imaging techniques in that it directly maps neuronal activity. This report describes our early experience with MSI in presurgical decision making of brain tumor patients here at Minnesota Epilepsy Group, PA. Four adult patients diagnosed with primary brain tumors underwent functional brain mapping with MSI (148-channel Magnes 2500 WH System, 4-D Neuroimaging, San Diego, CA) preoperatively using standard protocols for localization of language, somatosensory, and primary motor cortex. Data were analyzed using the single equivalent dipole model. Case 1 and Case 2 involved intra-axial, infiltrating tumors of the left frontal lobe, while Case 3 involved a similar lesion in the right frontal lobe. Case 4 had an extra-axial tumor originating from the midline, which appeared to be distorting the cortex. In Cases 1 and 2, MSI identified language cortex in close proximity to the tumor, including (for one patient) deep cortical areas not identified on cortical surface stimulation. In both cases, resection of the tumor was accomplished without creating a post-operative language deficit. In Case 3, a right frontal tumor was encroaching on primary motor cortex. MSI identified the margin of the motor area in relation to the tumor, allowing for maximal resection without causing any deficit. In Case 4, the somatosensory cortex was displaced by the tumor. The surgical approach was guided by MSI data, and confirmed by intra-operative somatosensory mapping. Following tumor resection, the patient recovered without deficit. MSI detects and maps the functional cortex in the sulcus. Cortical mapping delineates the superficial functional cortex. MSI plus cortical mapping can provide more accurate and complete functional information for surgical planning. This suggests the potential for practical clinical application of this new non-invasive technology to the presurgical evaluation of brain tumor cases on a routine basis.