TECHNIQUES AND APPLICATIONS FUNCTIONAL IDENTIFICATION OF THE PRIMARY MOTOR AREA BY CORTICOSPINAL TRACTOGRAPHY Kyousuke Kamada, M.D. Department of Neurosurgery, University of Tokyo, Tokyo, Japan Yutaka Sawamura, M.D. Department of Neurosurgery, Hokkaido University, Sapporo, Japan Fumiya Takeuchi, Ph.D. Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan Hideaki Kawaguchi, M.D. Department of Clinical Medicine, Hokkaido University, Sapporo, Japan Shinya Kuriki, Ph.D. Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan Tomoki Todo, M.D. Department of Neurosurgery, University of Tokyo, Tokyo, Japan Akio Morita, M.D. Department of Neurosurgery, University of Tokyo, Tokyo, Japan Yoshitaka Masutani, Ph.D. Department of Radiology, University of Tokyo, Tokyo, Japan Shigeki Aoki, M.D. Department of Radiology, University of Tokyo, Tokyo, Japan Takaaki Kirino, M.D. Department of Neurosurgery, University of Tokyo, Tokyo, Japan Reprint requests: Kyousuke Kamada, M.D., Department of Neurosurgery, Faculty of Medicine, University of Tokyo, Bunkyo-ku, Hongo 7-3-1, Tokyo 113-8655, Japan. Email: kamady-k@umin.ac.jp Received, November 12, 2003. Accepted, April 8, 2004. OBJECTIVE: For quick and stable identification of the primary motor area (PMA), diffusion tensor imaging (DTI) data were acquired and corticospinal tractography was mathematically visualized. METHODS: Data sets of DTI, anatomic magnetic resonance imaging, and functional magnetic resonance imaging with finger-tapping tasks were acquired during the same investigation in 30 patients with a brain lesion affecting the motor system. Off-line processing of DTI data was performed to visualize the corticospinal tract, placing a seed area in the cerebral peduncle of the midbrain, where the corticospinal tract is densely concentrated. Somatosensory evoked magnetic fields and intraoperative cor- tical somatosensory evoked potentials were recorded with electrical stimulation of the median nerve to confirm the results of the corticospinal tractography. RESULTS: Functional magnetic resonance imaging and somatosensory evoked mag- netic fields failed to identify the PMA in eight patients (16.7%) and one patient (3.8%) investigated, respectively, because of cortical dysfunctions caused by brain lesions. DTI data were acquired within 3 minutes without patient tasks. Using the appropriate seed area and fractional anisotropy, corticospinal tractography successfully indicated the PMA location in all patients. The suspected PMA and central sulcus locations were confirmed by the cortical somatosensory evoked potentials. CONCLUSION: Corticospinal tractography enables identification of the PMA and is beneficial, particularly for patients who present with dysfunction of the PMA. KEY WORDS: Corticospinal tract, Diffusion tensor imaging, Magnetoencephalography, Primary motor area, Tractography Neurosurgery 56[ONS Suppl 1]:ONS-98–ONS-109, 2005 DOI: 10.1227/01.NEU.0000144311.88383.EF N oninvasive functional brain mapping techniques such as magnetoencepha- lography (MEG) and functional mag- netic resonance imaging (fMRI) have been used routinely to identify the sensorimotor area for preoperative surgical planning. MEG reflects the intracellular electrical current flow in the brain, providing direct information re- garding neural activity. The somatosensory evoked magnetic field (SEF) has become the “gold standard” for identification of the cen- tral sulcus (CS) (5, 10, 11). Reduced SEF am- plitudes, however, may occasionally cause un- acceptable errors of dipole localization in patients with severe sensory impairment (8). It is well known that neuronal activation in- duces an increase in local blood flow, and fMRI detects local changes of the magnetic susceptibility of blood, demonstrating the blood oxygen level-dependent contrast. The crucial limitations encountered in fMRI-based brain mapping are the various degrees of ve- nous drainage architectures and regional he- modynamic responses in pathological brain conditions (1, 6, 8, 19). Furthermore, patients with cortical dysfunction such as hemiparesis or dementia can rarely achieve self-paced fin- ger tapping, which is a typical fMRI task for CS identification. There still remain several technical issues with noninvasive brain map- ping, and the results may be significantly af- fected by the patient’s condition. It is thus important to find a new technique for this purpose that can quickly complete the data acquisition process and subjectively make a secure identification of the sensorimotor area. Diffusion-weighted imaging has been dem- onstrated to be directionally dependent on ONS-98 | VOLUME 56 | OPERATIVE NEUROSURGERY 1 | JANUARY 2005 www.neurosurgery-online.com