Accuracy and limitation of functional magnetic resonance imaging for identification of the central sulcus: comparison with magnetoencephalography in patients with brain tumors

The aim of the present study was to clarify the accuracy and limitation of functional magnetic resonance imaging (fMRI) for the identification of the central sulcus affected by brain tumors. Twelve normal volunteers and 11 patients with intracranial tumors adjacent to the central sulcus underwent fMRI and magnetoencephalography (MEG). Three patients were evaluated again after surgery. fMRI was performed with a 1.5 Tesla scanner during repetitive opening and closing of each hand. Cross-correlation function was used to identify activation areas, and the central sulcus was defined as the nearest sulcus to the highest activation spots that were determined by elevating correlation coefficient threshold. Somatosensory-evoked fields were measured using a whole head MEG system. The central sulcus was defined as the nearest sulcus to the N20m for the median nerve stimulus. fMRI and MEG coincided in defining the central sulcus in all 24 hemispheres of volunteers and all 10 examined nonaffected hemispheres of patients. The fMRI-defined central sulcus coincided with the MEG-defined central sulcus in nine (82%) but did not in two (18%) affected hemispheres of patients. The preoperative mismatch disappeared after surgery in one of the two patients. The present study indicates that fMRI successfully defined the central sulcus in most of the patients with brain tumors. However, in a few cases, fMRI was not reliable probably due to venous flow changes by tumor compression and/or compensational activity by brain tissues surrounding the primary sensorimotor cortex. For precise functional assessment of the brain affected by intracranial tumors, combination of fMRI and MEG will be recommended.