Tag: CSF flow

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Measurement of CSF flow and brain motion in Chiari malformation type I subjects undergoing posterior fossa decompression surgery

J Neurosurg 143:13–23, 2025

Advanced MRI techniques show that in Chiari malformation type I, presurgical CSF flow and brain motion measurements better predict improvements after posterior fossa decompression surgery than traditional tonsillar descent metrics, potentially enabling more accurate identification of patients likely to benefit from surgery.

• Chiari malformation type I (CM-I) is defined by ≥5 mm cerebellar tonsil herniation through the foramen magnum, but tonsillar descent does not correlate well with symptom severity or surgical outcome.

• Posterior fossa decompression (PFD) surgery improves symptoms in ~75% of symptomatic CM-I patients, but carries risks, making optimal patient selection important.

• This study used advanced MRI (phase-contrast for CSF flow and DENSE for brain motion) to evaluate 108 CM-I patients, 61 of whom had PFD surgery.

• After PFD, CSF stroke volume increased by 28.9%, brainstem motion decreased by 17.3%, and cerebellar motion decreased by 45.2%.

• Improvements in CSF flow and brain motion after surgery were better predicted by presurgical CSF flow and brain motion, not by the amount of tonsillar descent.

• Presurgical dynamic measures (CSF flow, brain motion) are more informative for predicting surgical benefit than conventional anatomical metrics.

• These quantitative imaging assessments may help identify which patients will benefit most from surgery, improving patient care.

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Review of Cerebrospinal Fluid Physiology and Dynamics: A Call for Medical Education Reform

Neurosurgery 91:1–7, 2022

The flow of cerebrospinal fluid (CSF) has been described as a unidirectional system with the choroid plexus serving as the primary secretor of CSF and the arachnoid granulations as primary reabsorption site. This theory of neurosurgical forefathers has been universally adopted and taught as dogma. Many neuroscientists have found difficulty reconciling this theory with common pathologies, and recent studies have found that this “classic” hypothesis may not represent the full picture.

OBJECTIVE: To review modern CSF dynamic theories and to call formedical education reform.

METHODS: We reviewed the literature from January 1990 to December 2020. We searched the PubMed database using key terms “cerebrospinal fluid circulation,” “cerebrospinal fluid dynamics,” “cerebrospinal fluid physiology,” “glymphatic system,” and “glymphatic pathway.” We selected articles with a primary aim to discuss either CSF dynamics and/or the glymphatic system.

RESULTS: The Bulat–Klarica–Oreˇskovi´c hypothesis purports that CSF is secreted and reabsorbed throughout the craniospinal axis. CSF demonstrates similar physiology to that of water elsewhere in the body. CSF “circulates” throughout the subarachnoid space in a pulsatile to-and-fro fashion. Osmolarity plays a critical role in CSF dynamics. Aquaporin-4 and the glymphatic system contribute to CSF volume and flow by establishing osmolarity gradients and facilitating CSF movement. Multiple studies demonstrate that the choroid plexus does not play any significant role in CSF circulation.

CONCLUSION: We have highlighted major studies to illustrate modern principles of CSF dynamics. Despite these, the medical education system has been slow to reform curricula and update learning resources.

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Imaging-Based Features of Headaches in Chiari Malformation Type I

Imaging-Based Features of Headaches in Chiari Malformation Type I

Neurosurgery 77:96–103, 2015

Suboccipital cough-induced headaches are considered a hallmark symptom of Chiari malformation type I (CMI). However, non–Valsalva-related suboccipital headaches and headaches in other locations are also common in CMI. The diagnostic significance and the underlying factors associated with these different headaches types are not well understood.

OBJECTIVE: To compare cranial morphology and hydrodynamics in 3 types of headaches in CMI to better understand the pathophysiological basis for the different headache characteristics.

METHODS: Twenty-two cranial physiological and morphological measures were obtained with specialized magnetic resonance imaging scans from 63 symptomatic pretreated CMI patients, 40 with suboccipital headaches induced by Valsalva maneuvers (34 women; age, 36 6 10 years), 15 with non–Valsalva-related suboccipital headaches (10 women; age, 33 6 9 years), 8 with nonsuboccipital non–Valsalva-induced headaches (8 women; age, 39 6 13 years), and 37 control subjects (24 women; age, 36 6 12 years). Group differences were identified with the use of the 2-tailed Student t test. RESULTS: Posterior cranial fossa markers of CMI were similar among the 3 headache subtypes. However, the Valsalva-related suboccipital headaches cohort demonstrated a significantly lower intracranial compliance index than the non–Valsalva-related suboccipital headaches cohort (7.5 6 3.4 vs 10.9 6 4.9), lower intracranial volume change during the cardiac cycle (0.48 6 0.19 vs 0.61 6 0.16 mL), and higher magnetic resonance imaging–derived intracranial pressure (11.1 6 4.3 vs 7.7 6 2.8 mm Hg; P = .02). The Valsalva-related suboccipital headaches cohort had smaller intracranial and lateral ventricular volumes compared with the healthy cohort. The non–Valsalva-related suboccipital headaches cohort had reduced venous drainage through the jugular veins.

CONCLUSION: Valsalva-induced worsening of occipital headaches appears to be related to a small intracranial volume rather than the smaller posterior cranial fossa. This explains the reduced intracranial compliance and corresponding higher pressure measured in CMI patients with headaches affected by Valsalva maneuvers.

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Changes in cerebrospinal fluid flow assessed using intraoperative MRI during posterior fossa decompression for Chiari malformation

Changes in cerebrospinal fluid flow assessed using intraoperative MRI during posterior fossa decompression for Chiari malformation

J Neurosurg 122:1068–1075, 2015

The authors completed a prospective, institutional review board–approved study using intraoperative MRI (iMRI) in patients undergoing posterior fossa decompression (PFD) for Chiari I malformation. The purpose of the study was to examine the utility of iMRI in determining when an adequate decompression had been performed.

Methods Patients with symptomatic Chiari I malformations with imaging findings of obstruction of the CSF space at the foramen magnum, with or without syringomyelia, were considered candidates for surgery. All patients underwent complete T1, T2, and cine MRI studies in the supine position preoperatively as a baseline. After the patient was placed prone with the neck flexed in position for surgery, iMRI was performed. The patient then underwent a bone decompression of the foramen magnum and arch of C-1, and the MRI was repeated. If obstruction was still present, then in a stepwise fashion the patient underwent dural splitting, duraplasty, and coagulation of the tonsils, with an iMRI study performed after each step guiding the decision to proceed further.

Results Eighteen patients underwent PFD for Chiari I malformations between November 2011 and February 2013; 15 prone preincision iMRIs were performed. Fourteen of these patients (93%) demonstrated significant improvement of CSF flow through the foramen magnum dorsal to the tonsils with positioning only. This improvement was so notable that changes in CSF flow as a result of the bone decompression were difficult to discern.

Conclusions The authors observed significant CSF flow changes when simply positioning the patient for surgery. These results put into question intraoperative flow assessments that suggest adequate decompression by PFD, whether by iMRI or intraoperative ultrasound. The use of intraoperative imaging during PFD for Chiari I malformation, whether by ultrasound or iMRI, is limited by CSF flow dynamics across the foramen magnum that change significantly when the patient is positioned for surgery.

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Characterization of Cyclic CSF Flow in the Foramen Magnum and Upper Cervical Spinal Canal with MR Flow Imaging and Computational Fluid Dynamics

AJNR Am J Neuroradiol 31:997–1002.DOI 10.3174/ajnr.A1995

CSF flow has been shown to exhibit complex patterns in MR images in both healthy subjects and in patients with Chiari I. Abnormal CSF flow oscillations, according to prevailing opinion, cause syringomyelia and other clinical manifestations that affect some patients with the Chiari I malformation.

For this article, we reviewed the literature on PC MR of CSF flow, collected the published CFD studies relevant to CSF flow, and performed flow simulations. PC MR creates cine and still images of CSF flow and measurements of flow velocities. CFD, a technique used to compute flow and pressure in liquid systems, simulates the CSF flow patterns that occur in a specific geometry or anatomy of the SAS and a specific volume of flow.

Published PC MR studies show greater peak CSF velocities and more complex flow patterns in patients with Chiari I than in healthy subjects, with synchronous bidirectional flow one of the characteristic markers of pathologic flow. In mathematic models of the SAS created from high-resolution MR images, CFD displays complex CSF flow patterns similar to those shown in PC MR in patients. CFD shows that the pressure and flow patterns vary from level to level in the upper spinal canal and differ between patients with Chiari and healthy volunteers. In models in which elasticity and motion are incorporated, CFD displays CSF pressure waves in the SAS.

PC MR and CFD studies to date demonstrate significant alterations of CSF flow and pressure patterns in patients with Chiari I. CSF flow has nonlaminar complex spatial and temporal variations and associated pressure waves and pressure gradients. Additional simulations of CSF flow supplemented by PC MR will lead to better measures for distinguishing pathologic flow abnormalities that cause syringomyelia, headaches, and other clinical manifestations in Chiari I malformations.

CFD  computational fluid dynamics; PC MR  phase-contrast cardiac-gated MR studies; SAS  subarachnoid space

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