The present study discussed functional reorganization and alteration in respond to the slow-growing tumour,
hemangiopericytoma in the occipital cortex. Visual evoked field (VEF) and auditory evoked field (AEF) using
magnetoencephalography (MEG) was used to evaluate the source localization and brain activity. Results of VEF source
localization show a typical brain waves. Brain activity of the occipital lobe demonstrate low activation in the ipsilateral
to the tumour. However, result shows the activation on the contralateral hemisphere was high and bigger in activation
volume. AEF result shows an identical source localization and both side of the temporal lobe are activated. This result
suggests that there is a positive plasticity in auditory cortex and slow-growing tumour can induce functional reorganization
and alteration to the brain.