Why Intracranial Compliance Is Not Utilized as a Common Practical Tool in Clinical Practice

Abstract

Intracranial compliance (ICC) holds significant potential in neuromonitoring, serving as a diagnostic tool and contributing to the evaluation of treatment outcomes. Despite its comprehensive concept, which allows consideration of changes in both volume and intracranial pressure (ICP), ICC monitoring has not yet established itself as a standard component of medical care, unlike ICP monitoring. This review highlighted that the first challenge is the assessment of ICC values, because of the invasive nature of direct measurement, the time-consuming aspect of non-invasive calculation through computer simulations, and the inability to quantify ICC values in estimation methods. Addressing these challenges is crucial, and the development of a rapid, non-invasive computer simulation method could alleviate obstacles in quantifying ICC. Additionally, this review indicated the second challenge in the clinical application of ICC, which involves the dynamic and time-dependent nature of ICC. This was considered by introducing the concept of time elapsed (TE) in measuring the changes in volume or ICP in the ICC equation (volume change/ICP change). The choice of TE, whether short or long, directly influences the ICC values that must be considered in the clinical application of the ICC. Compensatory responses of the brain exhibit non-monotonic and variable changes in long TE assessments for certain disorders, contrasting with the mono-exponential pattern observed in short TE assessments. Furthermore, the recovery behavior of the brain undergoes changes during the treatment process of various brain disorders when exposed to short and long TE conditions. The review also highlighted differences in ICC values across brain disorders with various strain rates and loading durations on the brain, further emphasizing the dynamic nature of ICC for clinical application. The insight provided in this review may prove valuable to professionals in neurocritical care, neurology, and neurosurgery for standardizing ICC monitoring in practical application related to the diagnosis and evaluation of treatment outcomes in brain disorders.

Feasibility of assessing non-invasive intracranial compliance using FSI simulation-based and MR elastography-based brain stiffness

“…Despite optimism regarding the capabilities of MRE-based measurements of brain stiffness, concerns persist regarding their applicability across all types of brain disorders. Our recent study has differentiated brain disorders into two categories: gradual-onset and acute-onset 20 . Gradual-onset disorders, such as primary hydrocephalus or Alzheimer’s disease, exhibit symptoms that develop gradually, reflecting long-term load on the brain.…”

“…1 ) and serves as an important indicator for predicting clinical outcomes in a wide range of brain disorders such as hydrocephalus, traumatic brain injury, intracranial hypertension, and certain types of tumors and Chiari malformations 18 , 19 . Previous studies have shown that the primary known methods for directly measuring ICC involve the addition or removal of fluid in the craniospinal system 19 , 20 ; however, these experimental methods are invasive and carry inherent risks 20 . Furthermore, our recent studies have demonstrated notable variability in the methodologies of measuring ICC, highlighting concerns regarding their consistency and practical application in clinical settings 19 , 20 .…”

“…Previous studies have shown that the primary known methods for directly measuring ICC involve the addition or removal of fluid in the craniospinal system 19 , 20 ; however, these experimental methods are invasive and carry inherent risks 20 . Furthermore, our recent studies have demonstrated notable variability in the methodologies of measuring ICC, highlighting concerns regarding their consistency and practical application in clinical settings 19 , 20 . In the present study, a non-invasive computational approach was employed to calculate ICC as an alternative to measuring it using invasive methods.…”

“…The primary challenge in calculating ICC lies in determining ICP. Despite recent advances in medical imaging technology, the direct measurement of ICP through non-invasive imaging techniques remains unattainable 20 , 21 . Even invasive methods such as ICP monitoring do not provide comprehensive measurements of CSF pressure throughout the entire CSF circulation system.…”

“…Despite being a non-invasive FSI simulation method, computer simulation methods like FSI simulations are somewhat time-consuming to calculate ICC, similar to experimental invasive ICC measurement methods 20 , 28 . Hence, they cannot be the first option and the most efficient method to evaluate patients with an emergency condition.…”