The Monroe-Kellie doctrine describes intracranial pressure regulation. According to this doctrine, initial compensation for an expanding intracranial lesion is achieved primarily by:

• A Reduction in cerebral blood volume by arterial vasoconstriction
• B Increased CSF absorption through the arachnoid granulations
• C Cerebral oedema reduction through blood-brain barrier mechanisms
• D Displacement of CSF from the cranial vault into the spinal subarachnoid space ✓

Explanation

The Monro-Kellie doctrine states that the cranial vault is a rigid compartment containing brain tissue (~80%), blood (~12%), and CSF (~8%), whose total volume is constant. When a space-occupying lesion expands, initial compensation occurs by displacement of CSF from the cranial compartment to the spinal subarachnoid space (the most compliant and readily displaced component). Once CSF buffering capacity is exhausted, venous blood is displaced, and finally arterial blood displacement occurs, at which point further volume increase causes a sharp exponential rise in ICP (decompensation phase).

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.