The second theory posits that either increased blood flow to the brain or increase in the brain tissue itself may result in the raised pressure. Little evidence has accumulated to support the suggestion that increased blood flow plays a role, but recently Bateman et al. in phase contrast MRA studies have quantified cerebral blood flow (CBF) in vivo and suggests that CBF is abnormally elevated in many people with IIH. Both biopsy samples and various types of brain scans have shown an increased water content of the brain tissue. It remains unclear why this might be the case.