Which statement about the Monroe-Kellie doctrine is correct?

• A. The intracranial volume is fixed and includes brain tissue, blood, and CSF; if one component increases, another must be displaced.
• B. The skull can expand to accommodate increased brain tissue.
• C. CSF volume is constant and cannot be displaced.
• D. Intracranial pressure is unaffected by changes in blood volume.

Answer: (A)

The intracranial space is a fixed-volume compartment that contains brain tissue, blood, and CSF. Because the skull is rigid, the total volume cannot change; if one component increases, another must be displaced to keep the overall volume constant. This is why increases in brain tissue volume—such as edema or hemorrhage—drive displacement of CSF or venous blood, and why ICP rises only once the compensatory reserve is exhausted. The statement aligns with how compensation works and why it’s the best description of the Monroe-Kellie doctrine. The idea that the skull can expand is incorrect for adults, CSF cannot be displaced or ignored, and ICP does change with shifts in blood volume.