Monro-Kellie doctrine


The Monro-Kellie doctrine or hypothesis states that the sum of volumes of brain, cerebrospinal fluid (CSF) and intracerebral blood is constant. An increase in one should cause a reciprocal decrease in either one or both of the remaining two.

The doctrine is fundamental to our understanding of the negative effect of raised intracranial pressure on the brain.


1783 – Alexander Monro secundus published his observations on the structure and functioning of the nervous system. Given that the skull is a rigid compartment and the brain is “nearly incompressible”, Monro concluded that the amount of blood inside the skull should remain stable in normal and pathological conditions.

For, as the substance of the brain, like that of the other solids of our body, is nearly incompressible, the quantity of blood within the head must be the same, or very nearly the same, at all times, whether in health or disease, in life or after death, those cases only excepted, in which water or other matter is effused or secreted from the blood-vessels; for in these, a quantity of blood* equal in bulk to the effused matter, will be pressed out of the cranium.

[Monro, secundus 1783]

1824George Kellie was an Edinburgh based surgeon and former student of Monro. His contribution to the doctrine stems from papers he published on the post mortem examination of two individuals that were found deceased in Leith the morning after a winter storm.

The circulation within the head is, in truth, of a very peculiar description. The brain itself, little compressible, is contained within a firm and unyielding case of bone, which it exactly fills and by which it is defended from the weight and pressure of the atmosphere (…) a force, therefore, that must be constantly operating to maintain the plenitude of the vascular system within the head. If these premises be true, it does not appear very conceivable how any portion of the circulating fluid can ever be withdrawn from the cranium, without its place being simultaneously occupied by some equivalent; or how any thing new or exuberant can be intruded, without an equivalent displacement.

[Kellie, 1824]

1846 – Burrows introduced some changes to this hypothesis in his book On the disorders of the cerebral circulation, postulating that cerebral blood volume may vary but only to the benefit or the detriment of brain and CSF volumes

Associated Persons


the names behind the name

Studied at the University of Oxford - BA BM BCh. British doctor working in Emergency Medicine in Poole, Dorset. Special interests include respiratory medicine, critical care, and wilderness medicine.

BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

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