Which of the following is the third compensatory mechanism for maintaining intracranial volume when ICP rises?

Which of the following is the third compensatory mechanism for maintaining intracranial volume when ICP rises?

• A. Increased CSF production
• B. Expansion of intracranial veins
• C. Reabsorption of CSF across arachnoid villi into the dural venous sinus
• D. Decreased CSF production

Answer: (C)

When intracranial pressure (ICP) rises, the body works to keep the total intracranial volume in balance according to the Monro-Kellie principle. The first step is shifting CSF out of the cranial vault into the spinal subarachnoid space, and the second is adjusting venous outflow to reduce intracranial blood volume. If ICP continues to climb, the next line of defense is to increase the removal of CSF by reabsorbing it into the venous system through arachnoid villi (arachnoid granulations) into the dural venous sinuses. This CSF reabsorption lowers CSF volume and helps bring ICP back toward baseline, driven by the higher CSF pressure compared to venous pressure so CSF moves into the venous circulation. Increased CSF production would worsen the situation, expansion of intracranial veins would add to the venous volume rather than reduce it, and while decreasing CSF production could help, the established third compensatory mechanism is the reabsorption of CSF via arachnoid villi into the dural venous sinuses.

When intracranial pressure (ICP) rises, the body works to keep the total intracranial volume in balance according to the Monro-Kellie principle. The first step is shifting CSF out of the cranial vault into the spinal subarachnoid space, and the second is adjusting venous outflow to reduce intracranial blood volume. If ICP continues to climb, the next line of defense is to increase the removal of CSF by reabsorbing it into the venous system through arachnoid villi (arachnoid granulations) into the dural venous sinuses. This CSF reabsorption lowers CSF volume and helps bring ICP back toward baseline, driven by the higher CSF pressure compared to venous pressure so CSF moves into the venous circulation. Increased CSF production would worsen the situation, expansion of intracranial veins would add to the venous volume rather than reduce it, and while decreasing CSF production could help, the established third compensatory mechanism is the reabsorption of CSF via arachnoid villi into the dural venous sinuses.