It had been shown that high percentage of severe preeclampsia patients got a high cerebral perfusion pressure (CPP) due to abnormal autoregulation of cerebral blood vessels with associated endothelial dysfunction and disrupted blood brain barrier. Moreover, patients with high CPP is more likely to present with headache compared to other patients with normal CPP.In this particular scenario, use of magnesium sulphate is associated with marked reduction of CPP and. hence prevention of cerebral damage.This hypothesis was confirmed by new magnetic resonance techniques that demonstrated brain edema in eclampsia/ severe preeclampsia patient mostly due to vasogenic edema and less commonly attributed to cytotoxic edema.