Reducing CSF volume in the skull is proposed to decrease intracranial pressure and thereby increase cerebral perfusion. Which statement best describes this effect?

• A. It increases intracranial pressure
• B. It decreases intracranial pressure and increases cerebral perfusion
• C. It has no effect on perfusion
• D. It decreases brain ischemia but increases intracranial pressure

Answer: (B)

The key idea is that the skull is a fixed-volume container, so reducing one component’s volume (CSF) lowers the pressure inside the skull. Cerebral perfusion depends on the pressure gradient from the arteries into the brain, described by cerebral perfusion pressure (CPP) = mean arterial pressure minus intracranial pressure. When CSF volume is reduced and ICP falls while arterial pressure stays the same, CPP increases, allowing more blood to reach brain tissue (assuming autoregulation can respond). So the effect is a decrease in intracranial pressure with an accompanying increase in cerebral perfusion.