Monro-Kellie Hypothesis Research Articles

Assessment of increased intracranial pressure in patients with brain injury

Background: Monitoring and managing elevated intracranial pressure (ICP) is one of the core topics in neurocritical care. Although invasive methods are regarded as standard means, the recent development of non-invasive monitoring devices help clinicians handle ICP issues without additional risks of device-related complications.Current Concepts: According to the Monro–Kellie hypothesis, any brain injury that can cause a mass effect will lead to ICP elevation. Therefore, an ICP surge beyond the capacity of a compensatory reserve will decrease cerebral blood flow and may end up causing secondary brain damage. Indications for invasive ICP monitoring may vary according to the underlying conditions or the severity of brain damage. Regardless, ICP monitoring is considered when there is a risk of ICP elevation. In addition to pressure monitoring, external ventricular drainage catheters are used therapeutically to drain cerebrospinal fluid to reduce ICP. Several ICP monitoring probes are available based on pressure measurement types. Recently, non-invasive ICP monitoring methods have been developed and are increasingly used in patients with severe brain injuries. Pulsatility index from transcranial Doppler ultrasonography, quantitative pupillary light reflex from an automated pupillometer, and optic nerve sheath diameter using ultrasonography are commonly used surrogates for ICP surges in neurointensive care units.Discussion and Conclusion: ICP monitoring is essential for managing patients with severe brain injuries. Understanding the differences among the ICP monitors and determining the appropriate methods for ICP monitoring is necessary for optimizing patients’ care in the neurocritical care unit.

Spinal cord motion assessed by phase-contrast MRI - An inter-center pooled data analysis

BackgroundPhase-contrast MRI of CSF and spinal cord dynamics has evolved among diseases caused by altered CSF volume (spontaneous intracranial hypotension, normal pressure hydrocephalus) and by altered CSF space (degenerative cervical myelopathy (DCM), Chiari malformation). While CSF seems to be an obvious target for possible diagnostic use, craniocaudal spinal cord motion analysis offers the benefit of fast and reliable assessments. It is driven by volume shifts between the intracranial and the intraspinal compartments (Monro-Kellie hypothesis). Despite promising initial reports, comparison of spinal cord motion data across different centers is challenged by reports of varying value, raising questions about the validity of the findings. ObjectiveTo systematically investigate inter-center differences between phase-contrast MRI data. MethodsAge- and gender matched, retrospective, pooled-data analysis across two centers: cardiac-gated, sagittal phase-contrast MRI of the cervical spinal cord (segments C2/C3 to C7/T1) including healthy participants and DCM patients; comparison and analysis of different MRI sequences and processing techniques (manual versus fully automated). ResultsA genuine craniocaudal spinal cord motion pattern and an increased focal spinal cord motion among DCM patients were depicted by both MRI sequences (p < 0.01). Higher time-resolution resolved steeper and larger peaks, causing inter-center differences (p < 0.01). Comparison of different processing methods showed a high level of rating reliability (ICC > 0.86 at segments C2/C3 to C6/C7). DiscussionCraniocaudal spinal cord motion is a genuine finding. Differences between values were attributed to time-resolution of the MRI sequences. Automated processing confers the benefit of unbiased and consistent analysis, while data did not reveal any superiority.

Brain blood and cerebrospinal fluid flow dynamics during rhythmic handgrip exercise in young healthy men and women.

The cerebral fluid response to exercise, including the arterial and venous cerebral blood flow (CBF) and cerebrospinal fluid (CSF), currently remains unknown. We used time-resolved phase-contrast magnetic resonance imaging to assess changes in CBF and CSF flow dynamics during moderate-intensity rhythmic handgrip (RHG) exercise in young healthy men and women. Our data demonstrated that RHG increases the cerebral arterial inflow and venous outflow while decreasing the pulsatile CSF flow during RHG. Furthermore, changes in blood stroke volume at the measured arteries, veins, and sinuses and CSF stroke volume at the cerebral aqueduct were positively correlated with each other during RHG. Male and female participants exhibited distinct blood pressure responses to RHG, but their cerebral fluid responses were similar. These results collectively suggest that RHG influences both CBF and CSF flow dynamics in a way that is consistent with the Monro-Kellie hypothesis to maintain intracranial volume-pressure homeostasis in young healthy adults. Cerebral blood flow (CBF) increases during exercise, but its impact on cerebrospinal fluid (CSF) flow remains unknown. This study investigated CBF and CSF flow dynamics during moderate-intensity rhythmic handgrip (RHG) exercise in young healthy men and women. Twenty-six participants (12 women) underwent the RHG and resting control conditions in random order. Participants performed 3 sets of RHG, during which cine phase-contrast magnetic resonance imaging (PC-MRI) was performed to measure blood stroke volume (SV) and flow rate in the internal carotid (ICA) and vertebral (VA) arteries, the internal jugular vein (IJV), the superior sagittal (SSS) and straight sinuses (SRS), and CSF SV and flow rate in the cerebral aqueduct of Sylvius. Blood pressure, end-tidal CO2 (EtCO2 ), heart rate (HR), and respiratory rate were simultaneously measured during cine PC-MRI scans. Compared with control conditions, RHG showed significant elevations of HR, mean arterial pressure, and respiratory rate with a mild reduction of EtCO2 (all P < 0.05). RHG decreased blood SV in the measured arteries, veins, and sinuses and CSF SV in the aqueduct (all P < 0.05). Conversely, RHG increased blood flow in the ICA, VA, and IJV (all P < 0.05). At the aqueduct, RHG decreased the absolute CSF flow rate (P = 0.0307), which was calculated as a sum of the caudal and cranial CSF flow rates. Change in the ICA SV was positively correlated with changes in the IJV, SSS, SRS, and aqueductal SV during RHG (all P < 0.05). These findings demonstrate a close coupling between the CBF and CSF flow dynamics during RHG in young healthy adults.

Monro-Kellie Hypothesis: Increase of Ventricular CSF Volume after Surgical Closure of a Spinal Dural Leak in Patients with Spontaneous Intracranial Hypotension.

CSF loss in spontaneous intracranial hypotension disrupts a well-regulated equilibrium. We aimed to evaluate the volume shift between intracranial compartments in patients with spontaneous intracranial hypotension before and after surgical closure of the underlying spinal dural breach. In total, 19 patients with spontaneous intracranial hypotension with a proved spinal CSF leak investigated at our institution between July 2014 and March 2017 (mean age, 41.8 years; 13 women) were included. Brain MR imaging-based volumetry at baseline and after surgery was performed with FreeSurfer. In addition, the spontaneous intracranial hypotension score, ranging from 0 to 9, with 0 indicating very low and 9 very high probability of spinal CSF loss, was calculated. Total mean ventricular CSF volume significantly increased from baseline (15.3 mL) to posttreatment MR imaging (18.0 mL), resulting in a mean absolute and relative difference, +2.7 mL and +18.8% (95% CI, +1.2 to +3.9 mL; P < .001). The change was apparent in the early follow-up (mean, 4 days). No significant change in mean total brain volume was observed (1136.9 versus 1133.1 mL, P = .58). The mean spontaneous intracranial hypotension score decreased from 6.9 ± 1.5 at baseline to 2.9 ± 1.5 postoperatively. Our study demonstrated a substantial increase in ventricular CSF volume in the early follow-up after surgical closure of the underlying spinal dural breach and may provide a causal link between spinal CSF loss and spontaneous intracranial hypotension. The concomitant decrease in the spontaneous intracranial hypotension score postoperatively implies the restoration of an equilibrium within the CSF compartment.

Derivation of a Bleed to Brain Ratio to Predict the Need for Surgery in Head Injury.

The Monro-Kellie hypothesis states that the cranial compartment is incompressible, and cranial volume cannot expand. Human cranial volumes vary widely. However, the present guidelines for surgical evacuation are based on the volume of a single bleed. We hypothesized that the ratio of the total volume of blood clots in the brain to the volume of normal brain tissue must reflect the chances of developing increased intracranial pressure more accurately. Compare the ratio of bleed volume to intracranial brain volume (bleed--brain ratio, BBR) in head trauma patients who had undergone surgery with those who did not require surgery. Estimate the cutoff value for this ratio that could predict the need for surgery. An exact planimetric method using a Hounsfield unit bracketing strategy was used to derive total bleed volume and the intracranial volume in 212 head trauma patients. Receiver operating characteristics (ROC) curve was used to assess the predictive power of BBR for surgery. A cutoff value for the BBR with clinically significant sensitivity and specificity was estimated. The intracranial volume varied from 955 ml to a maximum of 1,525 ml. The total bleed volume and BBR was significantly different in the two groups. Using the ROC curve, we found that a BBR of 0.0535 had a sensitivity of 90.6% and a specificity of 52.6% to predict the need for surgery. We demonstrated that the BBR was superior to bleed volume alone in predicting the need for surgery. Although the ratio estimated by the tedious planimetric method was more accurate, an easier less precise method had reasonable accuracy and can be considered for everyday use. BBR could be particularly useful in those head trauma patients who have multiple irregular sized bleeds where the surgeon is undecided on the need for surgery.

Neurofluids: A holistic approach to their physiology, interactive dynamics and clinical implications for neurological diseases

There is increasing interest in understanding the physiology of the extracellular fluid compartments in the central nervous system and their dynamic interaction. Such interest has been in part prompted by a vigorous resurgence of the role of the venous system, the recent discoveries of the meningeal lymphatics, the brain waste removal mechanisms and their potential link to neurological diseases, such as idiopathic intracranial hypertension, Ménière’s disease, migraine, small vessel disease, and most neurodegenerative diseases. The rigid cranial cavity houses several space-competing material compartments: the brain parenchyma (BP) and four extracellular fluids, namely arterial, venous, cerebrospinal fluid (CSF) and interstitial fluid (ISF). During cardiac pulsations, the harmonious, temporal and spatial dynamic interaction of all these fluid compartments and the BP assures a constant intracranial volume at all times, consistent with the Monro-Kellie hypothesis. The dynamic interaction involves high-pressure input of arterial blood during systole and efflux of CSF into the spinal subarachnoid space (SSAS) followed by venous blood exiting directly into the vertebral and internal jugular veins towards the heart and intraventricular CSF displacing caudally towards the SSAS. Arterial pulsatile energy is transmitted to the BP that contributes to the smooth movement of fluids in and out of the brain. Perturbing any of these fluid compartments will alter the entire brain dynamics, potentially increase intracranial pressure, affect perfusion and hamper clearance capacity of metabolic waste. This review of all major extracellular fluid compartments within the brain, advocates a holistic approach to our understanding of the fluid dynamics, rather than focusing on a single compartment when analyzing neurological diseases. This approach may contribute to advance our comprehension of some common neurological disorders, paving the way to newer treatment options.

Superficial siderosis associated with duplicated dura mater detected by CISS reverse MRI

Superficial siderosis (SS) of the central nervous system is a rare disease caused by chronic or repeated hemorrhages in the subarachnoid space. Closure of dural defects is an effective therapy for SS. Conventional magnetic resonance imaging (MRI), however, cannot sufficiently detect dural tears. To better detect these defects, we analyzed the clinical data of consecutive patients admitted to our department with SS and performed constructive interference in steady-state (CISS) reverse MRI of the brain and spinal cord. CISS reverse method emphasizes the contrast between the dura and cerebrospinal fluid, enabling detection of dural defects better than usual T2-weighted MRI.CISS reverse MRI detected fluid-filled collections in five of the seven SS patients we studied. These images showed that the fluid-filled collections were packed within duplicated dura mater. In three of the five, dural defects were confirmed intraoperatively. We postulate that fluid-filled collections are actually derived from dissection of the dura mater. In accordance with the Monro-Kellie hypothesis, we propose that CSF transferal into the fluid-filled collections via dural defects induces an increase in blood volume and promotes the exudation of blood from engorged vessels.In patients with SS, it is very important to repair dural defects to prevent further associated neurological impairment. CISS reverse MRI is useful for detecting such dural defects.

External Ventricular Catheters: Is It Appropriate to Use an Open/Monitor Position to Adequately Trend Intracranial Pressure in a Neuroscience Critical Care Environment?

Intracranial pressure (ICP) monitoring can be an important assessment tool in critically and acutely ill patients. An external ventricular drain offers a comprehensive way to monitor ICP and drain cerebrospinal fluid. The Monro-Kellie hypothesis, Pascal's principle, and fluid dynamics were used to formulate an assumption that an open/monitor position on the stopcock is an adequate trending measure for ICP monitoring while concurrently draining cerebrospinal fluid. Data were collected from 50 patients and totaled 1053 separate number sets. The open/monitor position was compared with the clamped position every hour. An order for "open to drain" was needed for appropriate measurement and nursing care. Results showed the absolute average differences between open/monitor and clamped positions at 1.6268 mm Hg. This finding suggests that it is appropriate to use an open/monitor position via an external ventricular drain for adequate trending of patients' ICP.

Sagging brain development after lumbar puncture agrees with Monro-Kellie hypothesis

Sagging brain development after lumbar puncture agrees with Monro-Kellie hypothesis

Diffuse Pachymeningeal Enhancement and Subdural and Subarachnoid Space Opacification on Delayed Postcontrast Fluid-Attenuated Inversion Recovery Imaging in Spontaneous Intracranial Hypotension: Visualizing the Monro-Kellie Hypothesis: Fig 1.

Intracranial volume compensatory changes explained by the Monro-Kellie hypothesis (MKH) occur in spontaneous intracranial hypotension (SIH) and may be seen on MR imaging.[1][1] This case illustrates previously unreported findings on postcontrast fluid-attenuated inversion recovery (FLAIR) imaging

Hypothesis for lateral ventricular dilatation in communicating hydrocephalus: New understanding of the Monro-Kellie hypothesis in the aspect of cardiac energy transfer through arterial blood flow

Many theories have been postulated to date regarding mechanisms involved in non-enlargement of the subarachnoid space and enlargement of the ventricles in patients with communicating hydrocephalus, but none have been prove to be definite. Cerebrospinal fluid (CSF) movement is known not to bulk flow but rather pulsatile flow that develops from the energy of the blood flow ejected from the heart, in an isolated system of the intracranial cavity surrounded by a solid skull, as in the Monro-Kellie hypothesis. The authors attempt to explain the mechanisms involved in selective enlargement of the lateral ventricle in patients with communicating hydrocephalus by re-addressing the Monro-Kellie hypothesis with respect to cardiac energy transfer and dissipation by the Windkessel effect. The authors present a concept whereby the large energy of blood flow from the heart that is conveyed to the intracranial artery, arteriole, brain parenchyme, ventricle, and CSF within the confined cranial space as in the Monro-Kellie hypothesis, and which ultimately dissipates to maintain an intracranial energy equilibrium. In the same context, if, for some reason the intracranial equilibrium in the energy transfer and dissipation is changed or disrupted, then structural changes would have to occur to achieve and maintain a new intracranial equilibrium. We postulate that the above described mechanisms are those responsible for the development enlarged of lateral ventricles in patients with communicating hydrocephalus. Structural enlargement of the lateral ventricles in communicating hydrocephalus is a consequence of CSF pathway obstruction and resultantly increased CSF absorption function in the lateral ventricle which markedly increases the pulsatile CSF energy flow returning to the lateral ventricles, thus causing collision of pulsatile CSF flow with the brain parenchyme at the ventricular wall, which subsequently leads to structural enlargement of the lateral ventricles. Also, the collision between the CSF pulsation and brain parenchyme pulsation reduces the Windkessel effect of the brain parenchyme which increases the intracranial artery pulse pressure, which in turn is transmitted to the CSF and increases CSF pulse pressure. This vicious circle results in the high pulse pressure within the lateral ventricle structurally dilating the lateral ventricle. Our theory also explains the relationship between ventricle dilatation and idiopathic intracranial hypertension, venous sinus thrombosis, achondroplasia.

RAISED INTRACRANIAL PRESSURE

Raised intracranial pressure (ICP) is a common problem in neurosurgical and neurological practice. It can arise as a consequence of intracranial mass lesions, disorders of cerebrospinal fluid (CSF) circulation, and...

The Monro-Kellie hypothesis: applications in CSF volume depletion.

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.

Reply from the Author

Reply from the Author: According to Monro-Kellie hypothesis, the intracranial volume is constant when the skull is intact. Therefore, decrease in CSF volume would cause a compensatory vasodilatation in …

SOME LIMITATIONS OF THE MONRO-KELLIE HYPOTHESIS

For almost a century and a half, the hypothesis that the skull and bony coverings of the vertebral canal form a rigid container for the central nervous system has occupied the attention of anatomists, physiologists and neurologists. It is a hypothesis which has been gradually changed in its scope, and even in its conception, since its original promulgation by Alexander Monro1in 1783. Having been of interest to many in the course of the first fifty years of its existence, the doctrine has, in the past three decades, again become the subject of intensive investigation by workers in intracranial physiology. It is a tenet which has particularly concerned neurologic surgeons, because on its truth, or relative untruth, depend many of the critical procedures in the surgery of the central nervous system. The doctrine has especially intrigued the scientific curiosity of Harvey Cushing, to whom the academic world owes a