The Monro-Kellie doctrine was first described over two-hundred years ago by Dr. Alexander Monro and Dr. George Kellie. It describes the direct relationship between the contents of the cranium and intracranial pressure (Mokri, 2001). According to the Monro-Kellie doctrine, the contents of the cranium – which are the brain parenchyma, blood, and cerebrospinal fluid (CSF) – are constant/fixed (Amin-Hanjani & Smith, 2022). In adults, the intracranial compartment is protected by the skull, a rigid structure with a fixed internal volume of 1400-1700 mL (Amin-Hanjani & Smith, 2022). The brain parenchyma makes up 80% of that volume, the CSF makes up 10%, and the blood volume makes up 10%.

According to the Monro-Kellie doctrine, any increase in the volume of one component necessitates a decrease of the other components through compensatory mechanisms, an increase in intracranial pressure (ICP), or both (Amin-Hanjani & Smith, 2022). The normal value for ICP is 5-15 mmHg; a value above 20 mmHg requires prompt recognition and treatment (Benson, Carr, Cutsforth-Gregory, Johnson & Madhavan, 2022). Major causes of increased intracranial pressure include intracranial mass, cerebral edema, increased CSF production, decreased CSF absorption, obstructive hydrocephalus, obstruction of venous outflow, and idiopathic intracranial hypertension (pseudo tumor cerebri) (Amin-Hanjani & Smith, 2022).

The Monro-Kellie doctrine has been a fundamental principle for over two-hundred years in neurology/neurosurgery. It is a well-accepted principal that describes the relationship between intracranial contents and intracranial pressure.

References:

Benson, J. C., Madhavan, A. A., Cutsforth-Gregory, J. K., Johnson, D. R., & Carr, C. M. (2022). The Monro-Kellie Doctrine: A Review and Call for Revision. AJNR. American journal of neuroradiology, 10.3174/ajnr.A7721. Advance online publication. https://doi.org/10.3174/ajnr.A7721

Edward, S., Amin-Hanjani, S. (2022). Evaluation of management of elevated of intracranial pressure in adults. https://www.uptodate.com/contents/evaluation-and-management-of-elevated-intracranial-pressure-in-adults

Mokri B. (2001). The Monro-Kellie hypothesis: applications in CSF volume depletion. Neurology, 56(12), 1746–1748. https://doi.org/10.1212/wnl.56.12.1746