Cranial Cavity Constituents and Intracranial Pressure

Main Constituents of the Cranial Cavity

• The cranial cavity contains three main components:
  • Blood
    • Consists of both arterial and venous blood.
    • Volume: 150 ml (10% of the total volume).
  • Cerebral Spinal Fluid (CSF)
    • Volume: 150 ml (10% of the total volume).
  • Brain Tissue
    • Volume: 1400 ml (80% of the total volume).
• Total volume of the cranial cavity: 1700 ml.

Intracranial Pressure (ICP)

• Normal range: 7 to 15 millimeters of mercury.

Monroe-Kelly Doctrine

• Describes the relationship between the volumes in the cranial cavity:
  • Interchangeable Volume = Brain Volume + CSF Volume + Blood Volume.
• Because the skull is rigid, any increase in one of these volumes increases the overall intracranial volume and pressure.
• Compensation:
  • A small rise in one component (e.g., blood volume due to vasodilation) will cause the other two to decrease to maintain pressure and volume.
  • Protects the brain by maintaining constant pressure.

Impact of Significant Volume Increases

• Significant increases in volume, such as from a brain tumor, cannot be fully compensated by decreases in the other two components.
• Results in increased intracranial pressure, which can negatively impact the brain.

Upcoming Content

• Future discussions will cover further details on increases in intracranial pressure.