The Monro–Kellie hypothesis

Abstract

More than two centuries ago, Alexander Monro applied some of the principles of physics to the intracranial contents and for the first time hypothesized that the blood circulating in the cranium was of constant volume at all times. This hypothesis was supported by experiments by Kellie. In its original form, the hypothesis had shortcomings that prompted modification by others. What finally came to be known as the Monro-Kellie doctrine, or hypothesis, is that the sum of volumes of brain, CSF, and intracranial blood is constant. An increase in one should cause a decrease in one or both of the remaining two. This hypothesis has substantial theoretical implications in increased intracranial pressure and in decreased CSF volume. Many of the MRI abnormalities seen in intracranial hypotension or CSF volume depletion can be explained by the Monro-Kellie hypothesis. These abnormalities include meningeal enhancement, subdural fluid collections, engorgement of cerebral venous sinuses, prominence of the spinal epidural venous plexus, and enlargement of the pituitary gland.

Intraocular pressure correlates with optic nerve sheath diameter in patients with normal tension glaucoma

“…There is evidence that ICP may play a significant role in AH drainage by modulating ocular venous drainage [26]. According to the Monro-Kellie doctrine, intracranial blood volumes vary reciprocally with changes in the CSF volume [27]. Accordingly, a decrease or increase in CSF volume directly or indirectly influences the flow inside the intracranial venous sinuses, and therefore influences the drainage of the superior ophthalmic veins (SOVs).…”

CSF dynamic analysis of a predictive pulsatility-based infusion test for normal pressure hydrocephalus

“…The Monro-Kellie doctrine states that any increase in the volume of brain matter, blood or CSF must be compensated for by an equal decrease in the other volumes. [28] As brain matter is essentially incompressible, and the pressure in the arterial system exceeds that in the CSF or venous system, the normal compensatory shift of volume stems from venous blood and CSF. For a slow expansion increasing amounts of CSF can be absorbed, reducing the total CSF volume.…”

“…Within the rigid confines of the skull there is a limited amount of space and in accordance with the Monro-Kellie doctrine any increase in the volume of brain matter, blood or CSF must be compensated for by an equal decrease in the other volumes. [28] This leads to an interaction between the CSF dynamics and the hemodynamics, which is illustrated by the occurrence of ICP pulsations at the cardiac frequency caused by the transient increase of intracranial arterial blood occurring with each heart beat. To compensate for the increase venous blood is forced from the intracranial space, leading to pulsatile venous outflow, and CSF is forced into the spinal subarachnoid space, leading to oscillating flows within the CSF system.…”

Spontaneous intracranial hypotension with pituitary adenoma

“…Diffuse dural enhancement and prominent cavernous sinus represent the venous congestion that occurs to compensate the intracranial volume loss in accordance with the Monroe-Kellie doctrine [9].…”