Cerebellar and hindbrain motion in Chiari malformation with and without syringomyelia

Spinal cord motion and CSF flow in the cervical spine of 70 healthy participants

Pulsatile spinal cord and CSF velocities related to the cardiac cycle can be depicted by phase-contrast MRI. Among patients with spontaneous intracranial hypotension, we have recently described relevant differences compared with healthy controls in segment C2/C3. The method might be a promising tool to solve clinical and diagnostic ambiguities. Therefore, it is important to understand the physiological range and the effects of clinical and anatomical parameters in healthy volunteers. Within a prospective study, 3D T2-weighted MRI for spinal canal anatomy and cardiac-gated phase-contrast MRI adapted to CSF flow and spinal cord motion for time-resolved velocity data and derivatives were performed in 70 participants (age 20-79 years) in segments C2/C3 and C5/C6. Correlations were analyzed by multiple linear regression models; p < 0.01 was required to assume a significant impact of clinical or anatomical data quantified by the regression coefficient B. Data showed that in C2/C3, the CSF and spinal cord craniocaudal velocity ranges were 4.5 ± 0.9 and 0.55 ± 0.15 cm/s; the total displacements were 1.1 ± 0.3 and 0.07 ± 0.02 cm, respectively. The craniocaudal range of the CSF flow rate was 8.6 ± 2.4 mL/s; the CSF stroke volume was 2.1 ± 0.7 mL. In C5/C5, physiological narrowing of the spinal canal caused higher CSF velocity ranges and lower stroke volume (C5/C6 B = +1.64 cm/s, p < 0.001; B = -0.4 mL, p = 0.002, respectively). Aging correlated to lower spinal cord motion (e.g., B = -0.01 cm per 10 years of aging, p < 0.001). Increased diastolic blood pressure was associated with lower spinal cord motion and CSF flow parameters (e.g., C2/C3 CSF stroke volume B = -0.3 mL per 10 mmHg, p < 0.001). Males showed higher CSF flow and spinal cord motion (e.g., CSF stroke volume B = +0.5 mL, p < 0.001; total displacement spinal cord B = +0.016 cm, p = 0.002). We therefore propose to stratify data for age and sex and to adjust for diastolic blood pressure and segmental narrowing in future clinical studies.

A genetic component in Chiari I malformation: Chiari 1 malformation in all five family members

Under certain classifications, a Chiari type I (CMI) malformation can be characterized as a herniation of the cerebellar tonsils greater than 3 mm. Patients with CMI often have a smaller posterior fossa volume, which results in a smaller amount of space for the cerebellum, leading to the herniation of the cerebellar tonsils through the foramen magnum. Although inheritable factors such as posterior fossa volume can be traced to specific genes, there has not been a gene that can be attributed to directly causing CMI. However, several cases of CMI have exhibited a familial inheritance pattern. There are mixed findings regarding the exact nature of its inheritance, with some papers arguing in favor of an autosomal dominant pattern. In this case series, we detail a mother, father, and all 3 of their children diagnosed with CMI. Previous literature has not included both a mother and father with CMI.

Research process, recap, and prediction of Chiari malformation based on bicentennial history of nomenclature and terms misuse

There is an absent systematic analysis or review that has been conducted to clarify the topic of nomenclature history and terms misuse about Chiari malformations (CMs). We reviewed all reports on terms coined for CMs for rational use and provided their etymology and future development. All literature on the nomenclature of CMs was retrieved and extracted into core terms. Subsequently, keyword analysis, preceding and predicting (2023-2025) compound annual growth rate (CAGR) of each core term, was calculated using a mathematical formula and autoregressive integrated moving average model in Python. Totally 64,527 CM term usage was identified. Of these, 57 original terms were collected and then extracted into 24 core-terms. Seventeen terms have their own featured author keywords, while seven terms are homologous. The preceding CAGR of 24 terms showed significant growth in use for 18 terms, while 13, three, three, and five terms may show sustained growth, remain stable, decline, and rare in usage, respectively, in the future. Previously, owing to intricate nomenclature, Chiari terms were frequently misused, and numerous seemingly novel but worthless even improper terms have emerged. For a very basic neuropathological phenomenon tonsillar herniation by multiple etiology, a mechanism-based nosology seems to be more conducive to future communication than an umbrella eponym. However, a good nomenclature also should encapsulate all characteristics of this condition, but this is lacking in current CM research, as the pathophysiological mechanisms are not elucidated for the majority of CMs.

Association between resistance to cerebrospinal fluid flow and cardiac-induced brain tissue motion for Chiari malformation type I

PURPOSE

Chiari malformation type I (CMI) patients have been independently shown to have both increased resistance to cerebrospinal fluid (CSF) flow in the cervical spinal canal and greater cardiac-induced neural tissue motion compared to healthy controls. The goal of this paper is to determine if a relationship exists between CSF flow resistance and brain tissue motion in CMI subjects.

METHODS

Computational fluid dynamics (CFD) techniques were employed to compute integrated longitudinal impedance (ILI) as a measure of unsteady resistance to CSF flow in the cervical spinal canal in thirty-two CMI subjects and eighteen healthy controls. Neural tissue motion during the cardiac cycle was assessed using displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) technique.

RESULTS

The results demonstrate a positive correlation between resistance to CSF flow and the maximum displacement of the cerebellum for CMI subjects (r = 0.75, p = 6.77 × 10-10) but not for healthy controls. No correlation was found between CSF flow resistance and maximum displacement in the brainstem for CMI or healthy subjects. The magnitude of resistance to CSF flow and maximum cardiac-induced brain tissue motion were not statistically different for CMI subjects with and without the presence of five CMI symptoms: imbalance, vertigo, swallowing difficulties, nausea or vomiting, and hoarseness.

CONCLUSION

This study establishes a relationship between CSF flow resistance in the cervical spinal canal and cardiac-induced brain tissue motion in the cerebellum for CMI subjects. Further research is necessary to understand the importance of resistance and brain tissue motion in the symptomatology of CMI.

Congress of Neurological Surgeons Systematic Review and Evidence-Based Guidelines for Patients With Chiari Malformation: Diagnosis

BACKGROUND

Chiari I malformation (CIM) is characterized by descent of the cerebellar tonsils through the foramen magnum, potentially causing symptoms from compression or obstruction of the flow of cerebrospinal fluid. Diagnosis and treatment of CIM is varied, and guidelines produced through systematic review may be helpful for clinicians.

OBJECTIVE

To perform a systematic review of the medical literature to answer specific questions on the diagnosis and treatment of CIM.

METHODS

PubMed and Embase were queried between 1946 and January 23, 2021, using the search strategies provided in Appendix I of the full guidelines.

RESULTS

The literature search yielded 567 abstracts, of which 151 were selected for full-text review, 109 were then rejected for not meeting the inclusion criteria or for being off-topic, and 42 were included in this systematic review.

CONCLUSION

Three Grade C recommendations were made based on Level III evidence. The full guidelines can be seen online at https://www.cns.org/guidelines/browse-guidelines-detail/1-imaging .

Hemodynamic and Hydrodynamic Pathophysiology in Chiari Type 1 Malformations: Towards Understanding the Genesis of Syrinx

BACKGROUND

The pathophysiology of this association of type 1 Chiari malformation (CM1) and syrinxes is still unknown. There is an alteration in the dynamics of neurofluids (cerebrospinal fluid, arterial and venous blood) during the cardiac cycle in CM1. Our objective is to quantify CSF or arterial blood or venous blood flow in patients with Chiari syndrome (CS) with and without syrinxes using phase-contrast MRI (PCMRI).

METHODS

We included 28 patients with CM1 (9 with syrinxes, 19 without). Morphological MRI with complementary PCMRI sequences was performed. We analyzed intraventricular CSF, subarachnoid spaces CSF, blood, and tonsillar pulsatility.

RESULTS

There is a highly significant correlation (p < 0.001) between cerebral blood flow, cerebral vascular expansion volume and venous drainage distribution. Venous drainage distribution is significantly inversely correlated with oscillatory CSF volume at the level of the foramen magnum plane [-0.37 (0.04)] and not significantly correlated at the C2C3 level [-0.37 (0.05)] over our entire population. This correlation maintained the same trend in patients with syrinxes [-0.80 (<0.01)] and disappeared in patients without a syrinx [-0.05 (0.81)].

CONCLUSION

The distribution of venous drainage is an important factor in intracranial homeostasis. Impaired venous drainage would lead to greater involvement of the CSF in compensating for arterial blood influx, thus contributing to syrinx genesis.

Hypothesis on the pathophysiology of syringomyelia based on analysis of phase-contrast magnetic resonance imaging of Chiari-I malformation patients

Background: Despite several hypotheses, our understanding of syringomyelia's pathophysiology remains limited. The hypothesis proposed by Oldfield et al. suggests that piston-like movement of the cerebellar tonsils propels the cerebrospinal fluid (CSF) into the syrinx via the spinal perivascular space. However, a significant question remains unanswered: how does the CSF enter and stay in the syrinx, which has a higher pressure than the subarachnoid space. In the current study, we attempted to verify Oldfield's hypothesis using phase-contrast magnetic resonance imaging (MRI) data from patients with syringomyelia. Methods: We analyzed phase-contrast MRI scans of 18 patients with Chiari-I malformation associated with syringomyelia, all of whom underwent foramen magnum decompression, and 21 healthy volunteers. We obtained velocity waveforms for CSF and brain tissue from regions of interest (ROI) set at the various locations. These waveforms were synchronized at the peak timing of downward CSF flow. We compared the preoperative patient data with the control data and also compared the preoperative patient data with the postoperative patient data. Results: The syrinx shrank in 17 (94%) of the patients, and they experienced significant clinical improvement. When comparing pre- and postoperative MRI results, the only significant difference noted was the preoperative elevated velocity of the cerebellar tonsil, which disappeared post-surgery. The CSF velocities in the subarachnoid space were higher in the preoperative patients than in the controls, but they did not significantly differ in the postoperative MRI. The tonsillar velocity in the preoperative MRI was significantly lower than that of the CSF, suggesting that the elevated tonsillar velocity was more of an effect, rather than the cause, of the elevated CSF velocity. Conclusions: Given these findings, a completely new paradigm seems necessary. We, therefore, propose a novel hypothesis: the generative force of syringomyelia may be the direction-selective resistance to CSF flow in the subarachnoid space.

The Relationship Between Imbalance Symptom and Cardiac Pulsation Induced Mechanical Strain in the Brainstem and Cerebellum for Chiari Malformation Type I

Chiari malformation Type I (CMI) is known to have an altered biomechanical environment for the brainstem and cerebellum; however, it is unclear whether these altered biomechanics play a role in the development of CMI symptoms. We hypothesized that CMI subjects have a higher cardiac-induced strain in specific neurological tracts pertaining to balance, and postural control. We measured displacement over the cardiac cycle using displacement encoding with stimulated echoes magnetic resonance imaging in the cerebellum, brainstem, and spinal cord in 37 CMI subjects and 25 controls. Based on these measurements, we computed strain, translation, and rotation in tracts related to balance. The global strain on all tracts was small (<1%) for CMI subject and controls. Strain was found to be nearly doubled in three tracts for CMI subjects compared to controls (p < 0.03). The maximum translation and rotation were ∼150 μm and ∼1 deg, respectively and 1.5-2 times greater in CMI compared to controls in four tracts (p < 0.005). There was no significant difference between strain, translation, and rotation on the analyzed tracts in CMI subjects with imbalance compared to those without imbalance. A moderate correlation was found between cerebellar tonsillar position and strain on three tracts. The lack of statistically significant difference between strain in CMI subjects with and without imbalance could imply that the magnitude of the observed cardiac-induced strain was too small to cause substantial damage to the tissue (<1%). Activities such as coughing, or Valsalva may produce a greater strain.

A Critical Update of the Classification of Chiari and Chiari-like Malformations

Chiari malformations are a group of craniovertebral junction anomalies characterized by the herniation of cerebellar tonsils below the foramen magnum, often accompanied by brainstem descent. The existing classification systems for Chiari malformations have expanded from the original four categories to nine, leading to debates about the need for a more descriptive and etiopathogenic terminology. This review aims to examine the various classification approaches employed and proposes a simplified scheme to differentiate between different types of tonsillar herniations. Furthermore, it explores the most appropriate terminology for acquired herniation of cerebellar tonsils and other secondary Chiari-like malformations. Recent advances in magnetic resonance imaging (MRI) have revealed a higher prevalence and incidence of Chiari malformation Type 1 (CM1) and identified similar cerebellar herniations in individuals unrelated to the classic phenotypes described by Chiari. As we reassess the existing classifications, it becomes crucial to establish a terminology that accurately reflects the diverse presentations and underlying causes of these conditions. This paper contributes to the ongoing discussion by offering insights into the evolving understanding of Chiari malformations and proposing a simplified classification and terminology system to enhance diagnosis and management.

Cerebrospinal Fluid Hydrodynamics in Chiari I Malformation and Syringomyelia: Modeling Pathophysiology

Anatomic MRI, MRI flow studies, and intraoperative ultrasonography demonstrate that the Chiari I malformation obstructs CSF pathways at the foramen magnum and prevents normal CSF movement through the foramen magnum. Impaired CSF displacement across the foramen magnum during the cardiac cycle increases pulsatile hindbrain motion, pressure transmission to the spinal subarachnoid space, and the amplitude of CSF subarachnoid pressure waves driving CSF into the spinal cord. Central canal septations in adults prevent syrinx formation by CSF directly transmitting its pressure wave from the fourth ventricle to the central canal.

Compromised Cranio-Spinal Suspension in Chiari Malformation Type 1: A Potential Role as Secondary Pathophysiology

In Chiari Malformation Type I (CM1), low-lying tonsils obstruct the cisterna magna at the foramen magnum, thereby compromising the essential juncture between the cranial and spinal compartments. The anatomical obstruction of the cisterna magna inhibits bi-directional CSF flow as well as CSF pulse pressure equilibration between the intracranial compartment and the intraspinal compartment in response to instances of increased intracranial pressure. Less understood, however, are the roles of the spinal cord suspension structures at the craniocervical junction which lend viscoelastic support to the spinal cord and tonsils, as well as maintain the anatomical integrity of the cisterna magna and the dura. These include extradural ligaments including the myodural bridges (MDBs), as well as intradural dentate ligaments and the arachnoid framework. We propose that when these elements are disrupted by the cisterna magna obstruction, tonsillar pathology, and altered CSF dynamics, there may arise a secondary pathophysiology of compromised and dysfunctional cranio-spinal suspension in CM1. We present intraoperative images and videos captured during surgical exposure of the craniocervical junction in CM1 to illustrate this proposal.

Insights on the Hydrodynamics of Chiari Malformation

Background: We propose that the appearance of a ptosis of the cerebellar tonsils and syringomyelia is linked to its own hemohydrodynamic mechanisms. We aimed to quantify cerebrospinal fluid (CSF) and cerebral blood flow to highlight how neurofluid is affected by Chiari malformations type 1(CMI) and its surgery. Methods: We retrospectively included 21 adult patients with CMI who underwent pre- and postoperative phase contrast MRI (PCMRI) during the period from 2001 to 2017. We analyzed intraventricular CSF, subarachnoid spaces CSF, blood, and tonsils pulsatilities. Results: In preoperative period, jugular venous drainage seems to be less preponderant in patients with syringomyelia than other patients (venous correction factor: 1.49 ± 0.4 vs. 1.19 ± 0.1, p = 0.05). After surgery, tonsils pulsatility decreased significantly (323 ± 175 μL/cardiac cycle (CC) vs. 194 ± 130 μL/CC, p = 0.008) and subarachnoid CSF pulsatility at the foramen magnum increased significantly (201 ± 124 μL/CC vs. 363 ± 231 μL/CC, p = 0.02). After surgery, we found a decrease in venous flow amplitude (5578 ± 2469 mm3/s vs. 4576 ± 2084 mm3/s, p = 0.008) and venous correction factor (1.98 ± 0.3 vs. 1.20 ± 0.3 mm3/s, p = 0.004). Conclusions: Phase-contrast MRI could be a useful additional tool for postoperative evaluation and follow-up, and is complementary to morphological imaging.

Spontaneous Resolution of Aberrant Cerebellar Tonsil Movement in a Patient with Improving Chiari I Malformation

Chiari malformation Type 1 (CMI) is traditionally characterized as a descent of the cerebellar tonsils more than 5mm below the foramen magnum. In some patients with CMI, there is aberrant pulsatile movement of the tonsils downward during cardiac systole which can affect cerebrospinal fluid (CSF) flow at the foramen magnum. Here, we present an 18-year-old female patient with CMI who presented with worsening symptoms of her CMI. Magnetic resonance imaging (MRI) at this time indicated an increase in cerebellar tonsil movement and decreased CSF flow at the foramen magnum. At her follow-up appointment, she had complete resolution of the aberrant motion of her tonsils and CSF flow returned to baseline without surgical intervention. Her symptoms also improved during this time, and she is now able to be followed by her primary care physician. The increased pulsatile movement of cerebellar tonsils in patients with CMI has been linked to diminished CSF flow at the foramen magnum and symptom severity. Spontaneous resolution of CMI is rare and has only ever been documented as ascension of the cerebellar tonsils. This case describes restoration of normal tonsil movement and baseline CSF flow corresponding with a resolution of symptoms where a complete resolution in tonsillar ectopia was not present.

Syringomyelia intermittens: highlighting the complex pathophysiology of syringomyelia. Illustrative case

BACKGROUND

Chiari Type I malformation (CM1) is a disorder recognized by caudal displacement of the cerebellar tonsils through the foramen magnum and into the cervical canal. Syringomyelia is frequently found in patients with CM1, but the pathophysiology of syringomyelia remains an enigma. As a general consensus, symptomatic patients should be treated and asymptomatic patients without a syrinx should not be treated. Mildly symptomatic patients or asymptomatic patients with a syrinx, on the other hand, pose a more challenging dilemma, as the natural evolution is uncertain. For many surgeons, the presence of a syrinx is an indication to offer surgery even if the patient is asymptomatic or mildly symptomatic.

OBSERVATIONS

The authors describe an illustrative case of a 31-year-old female with an incidental finding of a CM1 malformation and cervical syrinx in 2013. Conservative management was advocated as the patient was asymptomatic. Monitoring of the syrinx over a course of 8 years showed resolution, followed by reappearance and finally a complete resolution in 2021. A review of the literature and the possible pathophysiology is discussed.

LESSONS

The unusual course of this patient highlights the importance of guiding treatment by clinical symptoms, not radiological findings. Furthermore it reflects the complexity of the pathophysiology and the uncertain natural history of syringomyelia.

Cerebellar and Brainstem Displacement Measured with DENSE MRI in Chiari Malformation Following Posterior Fossa Decompression Surgery

Background Posterior fossa decompression (PFD) surgery is a treatment for Chiari malformation type I (CMI). The goals of surgery are to reduce cerebellar tonsillar crowding and restore posterior cerebral spinal fluid flow, but regional tissue biomechanics may also change. MRI-based displacement encoding with stimulated echoes (DENSE) can be used to assess neural tissue displacement. Purpose To assess neural tissue displacement by using DENSE MRI in participants with CMI before and after PFD surgery and examine associations between tissue displacement and symptoms. Materials and Methods In a prospective, HIPAA-compliant study of patients with CMI, midsagittal DENSE MRI was performed before and after PFD surgery between January 2017 and June 2020. Peak tissue displacement over the cardiac cycle was quantified in the cerebellum and brainstem, averaged over each structure, and compared before and after surgery. Paired t tests and nonparametric Wilcoxon signed-rank tests were used to identify surgical changes in displacement, and Spearman correlations were determined between tissue displacement and presurgery symptoms. Results Twenty-three participants were included (mean age ± standard deviation, 37 years ± 10; 19 women). Spatially averaged (mean) peak tissue displacement demonstrated reductions of 46% (79/171 µm) within the cerebellum and 22% (46/210 µm) within the brainstem after surgery (P < .001). Maximum peak displacement, calculated within a circular 30-mm² area, decreased by 64% (274/427 µm) in the cerebellum and 33% (100/300 µm) in the brainstem (P < .001). No significant associations were identified between tissue displacement and CMI symptoms (r < .74 and P > .012 for all; Bonferroni-corrected P = .0002). Conclusion Neural tissue displacement was reduced after posterior fossa decompression surgery, indicating that surgical intervention changes brain tissue biomechanics. For participants with Chiari malformation type I, no relationship was identified between presurgery tissue displacement and presurgical symptoms. © RSNA, 2021 Online supplemental material is available for this article.

Regional Brain Tissue Displacement and Strain is Elevated in Subjects with Chiari Malformation Type I Compared to Healthy Controls: A Study Using DENSE MRI

While the degree of cerebellar tonsillar descent is considered the primary radiologic marker of Chiari malformation type I (CMI), biomechanical forces acting on the brain tissue in CMI subjects are less studied and poorly understood. In this study, regional brain tissue displacement and principal strains in 43 CMI subjects and 25 controls were quantified using a magnetic resonance imaging (MRI) methodology known as displacement encoding with stimulated echoes (DENSE). Measurements from MRI were obtained for seven different brain regions-the brainstem, cerebellum, cingulate gyrus, corpus callosum, frontal lobe, occipital lobe, and parietal lobe. Mean displacements in the cerebellum and brainstem were found to be 106 and 64% higher, respectively, for CMI subjects than controls (p < .001). Mean compression and extension strains in the cerebellum were 52 and 50% higher, respectively, in CMI subjects (p < .001). Brainstem mean extension strain was 41% higher in CMI subjects (p < .001), but no significant difference in compression strain was observed. The other brain structures revealed no significant differences between CMI and controls. These findings demonstrate that brain tissue displacement and strain in the cerebellum and brainstem might represent two new biomarkers to distinguish between CMI subjects and controls.

Association Between Resistance to Cerebrospinal Fluid Flow Near the Foramen Magnum and Cough-Associated Headache in Adult Chiari Malformation Type I

Cough-associated headaches (CAHs) are thought to be distinctive for Chiari malformation type I (CMI) patients and have been shown to be related to the motion of cerebrospinal fluid (CSF) near the foramen magnum (FM). We used computational fluid dynamics (CFD) to compute patient-specific resistance to CSF motion in the spinal canal for CMI patients to determine its accuracy in predicting CAH. Fifty-one symptomatic CMI patients with cerebellar tonsillar position (CTP) ≥ 5 mm were included in this study. The patients were divided into two groups based on their symptoms (CAH and non-CAH) by review of the neurosurgical records. CFD was utilized to simulate CSF motion, and the integrated longitudinal impedance (ILI) was calculated for all patients. A receiver operating characteristic (ROC) curve was evaluated for its accuracy in predicting CAH. The ILI for CMI patients with CAH (776 dyn/cm5, 288-1444 dyn/cm5; median, interquartile range) was significantly larger compared to non-CAH (285 dyn/cm5, 187-450 dyn/cm5; p = 0.001). The ILI was more accurate in predicting CAH in CMI patients than the CTP when the comparison was made using the area under the ROC curve (AUC) (0.77 and 0.70, for ILI and CTP, respectively). ILI ≥ 750 dyn/cm5 had a sensitivity of 50% and a specificity of 95% in predicting CAH. ILI is a parameter that is used to assess CSF blockage in the spinal canal and can predict patients with and without CAH with greater accuracy than CTP.

Pulsatile cerebrospinal fluid dynamics in Chiari I malformation syringomyelia: Predictive value in posterior fossa decompression and insights into the syringogenesis

Background:

Pathophysiological mechanisms underlying the syringomyelia associated with Chiari I malformation (CM-1) are still not completely understood, and reliable predictors of the outcome of posterior fossa decompression (PFD) are lacking accordingly. The reported prospective case-series study aimed to prove the existence of a pulsatile, biphasic systolic–diastolic cerebrospinal fluid (CSF) dynamics inside the syrinx associated with CM-1 and to assess its predictive value of patients' outcome after PFD. Insights into the syringogenesis are also reported.

Methods:

Fourteen patients with symptomatic CM-1 syringomyelia underwent to a preoperative neuroimaging study protocol involving conventional T1/T2 and cardiac-gated cine phase-contrast magnetic resonance imaging sequences. Peak systolic and diastolic velocities were acquired at four regions of interest (ROIs): syrinx, ventral, and dorsal cervical subarachnoid space and foramen magnum region. Data were reported as mean ± standard deviation. After PFD, the patients underwent a scheduled follow-up lasting 3 years. One-way analysis of variance with Bonferroni Post hoc test of multiple comparisons was performed P was <0.001.

Results:

All symptoms but atrophy and spasticity improved. PFD caused a significant velocity changing of each ROI. Syrinx and premedullary cistern velocities were found to be decreased within the 1^st month after PFD (<0.001). A caudad and cephalad CSF jet flow was found inside the syrinx during systole and diastole, respectively.

Conclusion:

Syrinx and premedullary cistern velocities are related to an early improvement of symptoms in patients with CM-1 syringomyelia who underwent PFD. The existence of a biphasic pulsatile systolic–diastolic CSF pattern inside the syrinx validates the “transmedullary” theory about the syringogenesis.

Amplified Flow Imaging (aFlow): A Novel MRI-Based Tool to Unravel the Coupled Dynamics Between the Human Brain and Cerebrovasculature

With each heartbeat, periodic variations in arterial blood pressure are transmitted along the vasculature, resulting in localized deformations of the arterial wall and its surrounding tissue. Quantification of such motions may help understand various cerebrovascular conditions, yet it has proven technically challenging thus far. We introduce a new image processing algorithm called amplified Flow (aFlow) which allows to study the coupled brain-blood flow motion by combining the amplification of cine and 4D flow MRI. By incorporating a modal analysis technique known as dynamic mode decomposition into the algorithm, aFlow is able to capture the characteristics of transient events present in the brain and arterial wall deformation. Validating aFlow, we tested it on phantom simulations mimicking arterial walls motion and observed that aFlow displays almost twice higher SNR than its predecessor amplified MRI (aMRI). We then applied aFlow to 4D flow and cine MRI datasets of 5 healthy subjects, finding high correlations between blood flow velocity and tissue deformation in selected brain regions, with correlation values r = 0.61 , 0.59, 0.52 for the pons, frontal and occipital lobe ( ). Finally, we explored the potential diagnostic applicability of aFlow by studying intracranial aneurysm dynamics, which seems to be indicative of rupture risk. In two patients, aFlow successfully visualized the imperceptible aneurysm wall motion, additionally quantifying the increase in the high frequency wall displacement after a one-year follow-up period (20%, 76%). These preliminary data suggest that aFlow may provide a novel imaging biomarker for the assessment of aneurysms evolution, with important potential diagnostic implications.

Accuracy of cardiac-induced brain motion measurement using displacement-encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI): A phantom study

PURPOSE

The goal of this study was to determine the accuracy of displacement-encoding with stimulated echoes (DENSE) MRI in a tissue motion phantom with displacements representative of those observed in human brain tissue.

METHODS

The phantom was comprised of a plastic shaft rotated at a constant speed. The rotational motion was converted to a vertical displacement through a camshaft. The phantom generated repeatable cyclical displacement waveforms with a peak displacement ranging from 92 µm to 1.04 mm at 1-Hz frequency. The surface displacement of the tissue was obtained using a laser Doppler vibrometer (LDV) before and after the DENSE MRI scans to check for repeatability. The accuracy of DENSE MRI displacement was assessed by comparing the laser Doppler vibrometer and DENSE MRI waveforms.

RESULTS

Laser Doppler vibrometer measurements of the tissue motion demonstrated excellent cycle-to-cycle repeatability with a maximum root mean square error of 9 µm between the ensemble-averaged displacement waveform and the individual waveforms over 180 cycles. The maximum difference between DENSE MRI and the laser Doppler vibrometer waveforms ranged from 15 to 50 µm. Additionally, the peak-to-peak difference between the 2 waveforms ranged from 1 to 18 µm.

CONCLUSION

Using a tissue phantom undergoing cyclical motion, we demonstrated the percent accuracy of DENSE MRI to measure displacement similar to that observed for in vivo cardiac-induced brain tissue.

Cerebellar Tissue Strain in Chiari Malformation with Headache

OBJECTIVE

The pathogenesis of Chiari malformation type 1 (CM-1)-associated Valsalva headache is unknown, but it may be caused by abnormal cerebellar tonsil tissue strain. Advances in cardiac-gated magnetic resonance imaging (MRI) techniques such as balanced fast-field echo (bFFE) allow quantification of the motion of anatomic structures and can be used to measure tissue strain. The current study investigated the relationship between Valsalva heachache and tonsillar motion in patients with CM-1.

METHODS

A retrospective review of patients with CM-1 who had undergone cardiac-gated bFFE MRI was performed. Headache symptoms were retrieved from the medical records. Anatomic landmarks were manually selected on the cine bFFE, and a validated motion-tracking software was used to assess motion over the cardiac cycle in patients at rest. For each patient, displacement, strain, and strain rate were calculated for 3 anatomic segments. Patients undergoing surgery were examined before and after surgery.

RESULTS

From 88 patients, a total of 108 bFFE sequences were analyzed. Valsalva headache was present in 50% of patients. Cerebellar tonsil displacement (P = 0.003), strain (P = 0.012), and maximum strain rate (P = 0.04) were reduced after surgery (n = 20). There was no statistically significant association between tissue motion and headache symptoms.

CONCLUSION

The results of this study do not support a relationship between cardiac cycle cerebellar strain and Valsalva headache in patients with CM-1. It is possible that cerebellar strain related to respiratory maneuvers is associated with headache in Chiari patients. Further investigation of tissue strain is warranted because it represents a potential biomarker for outcomes after surgery.

A Computational Model for the Dynamics of Cerebrospinal Fluid in the Spinal Subarachnoid Space

Global models for the dynamics of coupled fluid compartments of the central nervous system (CNS) require simplified representations of the individual components which are both accurate and computationally efficient. This paper presents a one-dimensional model for computing the flow of cerebrospinal fluid (CSF) within the spinal subarachnoid space (SSAS) under the simplifying assumption that it consists of two coaxial tubes representing the spinal cord and the dura. A rigorous analysis of the first-order nonlinear system demonstrates that the system is elliptic-hyperbolic, and hence ill-posed, for some values of parameters, being hyperbolic otherwise. In addition, the system cannot be written in conservation-law form, and thus, an appropriate numerical approach is required, namely the path conservative approach. The designed computational algorithm is shown to be second-order accurate in both space and time, capable of handling strongly nonlinear discontinuities, and a method of coupling it with an unsteady inflow condition is presented. Such an approach is sufficiently rapid to be integrated into a global, closed-loop model for computing the dynamics of coupled fluid compartments of the CNS.

Regional Quantification of Brain Tissue Strain Using Displacement-Encoding With Stimulated Echoes Magnetic Resonance Imaging

Intrinsic cardiac-induced deformation of brain tissue is thought to be important in the pathophysiology of various neurological disorders. In this study, we evaluated the feasibility of utilizing displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) to quantify two-dimensional (2D) neural tissue strain using cardiac-driven brain pulsations. We examined eight adult healthy volunteers with an electrocardiogram-gated spiral DENSE sequence performed at the midsagittal plane on a 3 Tesla MRI scanner. Displacement, pixel-wise trajectories, and principal strains were determined in seven regions of interest (ROI): the brain stem, cerebellum, corpus callosum, and four cerebral lobes. Quantification of small neural tissue motion and strain along with their spatial and temporal variations in different brain regions was found to be feasible using DENSE. The medial and inferior brain structures (brain stem, cerebellum, and corpus callosum) had significantly larger motion and strain compared to structures located more peripherally. The brain stem had the largest peak mean displacement (PMD) (187 ± 50 μm, mean ± SD). The largest mean principal strains in compression and extension were observed in the brain stem (0.38 ± 0.08%) and the corpus callosum (0.37 ± 0.08%), respectively. Measured values in percent strain were altered by as much as 0.1 between repeated scans. This study showed that DENSE can quantify regional variations in brain tissue motion and strain and has the potential to be utilized as a tool to evaluate the changes in brain tissue dynamics resulting from alterations in biomechanical stresses and tissue properties.

Cardiac-Related Spinal Cord Tissue Motion at the Foramen Magnum is Increased in Patients with Type I Chiari Malformation and Decreases Postdecompression Surgery

OBJECTIVE

Type 1 Chiari malformation (CM-I) is a craniospinal disorder historically defined by cerebellar tonsillar position greater than 3-5 mm below the foramen magnum (FM). This definition has come under question because quantitative measurements of cerebellar herniation do not always correspond with symptom severity. Researchers have proposed several additional radiographic diagnostic criteria based on dynamic motion of fluids and/or tissues. The present study objective was to determine if cardiac-related craniocaudal spinal cord tissue displacement is an accurate indicator of the presence of CM-I and if tissue displacement is altered with decompression.

METHODS

A cohort of 20 symptomatic patients underwent decompression surgery. Fifteen healthy volunteers were recruited for comparison with the CM-I group. Axial phase-contrast magnetic resonance imaging (PC-MRI) measurements were collected before and after surgery at the FM with cranial-caudal velocity encoding and 20 frames per cardiac cycle with retrospective reconstruction. Spinal cord motion (SCM) at the FM was quantified based on the peak-to-peak integral of average spinal cord velocity.

RESULTS

Tissue motion for the presurgical group was significantly greater than controls (P = 0.0009). Motion decreased after surgery (P = 0.058) with an effect size of -0.151 mm and a standard error of 0.066 mm. Postoperatively, no statistical difference from controls in bulk displacement at the FM was found (P = 0.200) after post hoc testing using the Tukey adjustment for multiple comparisons.

CONCLUSIONS

These results support SCM measurement by PC-MRI as a possible noninvasive radiographic diagnostic for CM-I. Dynamic measurement of SCM provides unique diagnostic information about CM-I alongside static quantification of tonsillar position and other intracranial morphometrics.

Dorsal extensions of the fastigium cerebelli: an anatomical study using magnetic resonance imaging

BACKGROUND AND PURPOSE

The fastigium cerebelli is an important topographical landmark for neurosurgeons and radiologists. However, few studies have characterized the morphology of the fastigium cerebelli. We aimed to investigate the fastigium cerebelli using postmortem specimens and magnetic resonance imaging (MRI) in vivo.

MATERIALS AND METHODS

Three cadaveric brains were midsagittally sectioned for observing the fastigium cerebelli. Additionally, 66 outpatients underwent MRI, including sagittal T1-weighted imaging, axial T2-weighted imaging, and coronal constructive interference in steady-state (CISS) sequence.

RESULTS

In the cadaveric specimens, the fastigium cerebelli was observed as a beak-like dorsal protrusion of the fourth ventricle. Its inner surface was observed as a small fovea. On serial CISS images, the fastigium cerebelli consistently possessed a pair of triangular-shaped, dorsal extensions lying parasagittally along the nodule. These extensions were classified as symmetrical, right-side dominant, or left-side dominant. The symmetrical type was the most predominant and comprised 60.6% of the extensions, while the right-side dominant and left-side dominant types comprised 13.6 and 25.8%, respectively. In 91% of the 66 patients, the number of slices covering the entirety of the dorsal extensions were the same on both sides. The fastigial angle (θ) formed by lines tangent to the superior and inferior medullary velums varied widely.

CONCLUSIONS

The fastigium cerebelli has a pair of dorsal extensions lying parasagittally along the nodule. Coronal CISS sequence is useful in delineating the fastigium cerebelli in vivo.

A Systematic Review of Cognition in Chiari I Malformation

Displacement of the cerebellar tonsils in Chiari type I malformation (CMI) can affect functions controlled by the cerebellum and brainstem. While playing an integral role in the control of movement, the cerebellum also has widespread cortical connections, influencing a range of cognitive process. A systematic literature review was conducted to examine the relationship between cognition and CMI, assessing evidence for general or domain-specific cognitive change. The search protocol examined the AMED, CINAHL, Cochrane Library, EMBASE, MEDLINE, PsycINFO, and Scopus databases. Articles meeting the following criteria were included in this review (i) examined children or adults with a clinically defined diagnosis of CMI, (ii) assessed cognitive function with a prospective examination, (iii) included at least one standardized instrument designed to measure general or specific domains of cognitive function, and (iv) were published in English in a peer-reviewed journal. Twelve articles were identified, including 783 cases aged 3 months to 64 years. General cognition, processing speed, and learning and memory appeared less affected, while language deficits appeared to diminish with age. Executive dysfunction was the most commonly reported cognitive impairment, while attention and working memory, and visuospatial and perceptual skills also appeared vulnerable. Numerous methodological limitations were identified that should be considered in interpreting the impact of CMI and planning future investigations. Overall, there is currently insufficient evidence to describe a valid and reliable profile of cognitive impairment in CMI. Further research is required to confirm these preliminary psychometric results and integrate them with pathophysiological models.

Treatment of Syringomyelia in Patients with Arachnoiditis at the Craniocervical Junction

OBJECTIVE

Craniocervical junction arachnoiditis (CCJA) is an uncommon cause of syringomyelia. The pathophysiology of syrinx formation is uncertain, and the appropriate management unclear. A series of cases is reported to demonstrate variations in etiology, uniformity of functional cerebrospinal fluid obstruction at the foramen magnum, and results of surgical intervention.

METHODS

We retrospectively analyzed the clinical and radiologic features of a consecutive series of patients treated for syringomyelia related to CCJA.

RESULTS

Eight patients (5 male, 28-66 years old) were treated from 2000 to 2016. Magnetic resonance imaging demonstrated cervicothoracic syringomyelia in all cases, with the rostral extension of the syrinx suggesting communication with the fourth ventricle in all but one case. There was reduction of foramen magnum cerebrospinal fluid space in all cases, cerebellar ectopia in 5 cases, and fourth ventricular entrapment in 3 cases. Treatment consisted of posterior fossa decompression with either a GoreTex or pericranial patch graft. Six patients had a fourth-ventricle spinal subarachnoid shunt. Two patients had titanium mesh cranioplasty. The immediate postoperative period was associated with reduction in syrinx cavity size and improvement in neurologic symptoms in all cases. At follow-up 10-60 months postoperatively, 3 patients exhibited recurrence of the syrinx and underwent successful reoperation at the craniocervical junction. One patient with persistence of the inferior component of the syrinx was treated with a syrinx-spinal subarachnoid shunt.

CONCLUSIONS

Most syrinx cavities associated with CCJA communicate with the fourth ventricle. Posterior fossa decompression and fourth ventricle to spinal subarachnoid space shunting appears a reasonable treatment for this form of syringomyelia.

"Stealth cranioplasty:" A novel endeavor for symptomatic adult Chiari I patients with syringomyelia: Technical note, appraisal, and philosophical considerations

Aim and Objective:

In this article, we describe a novel technique of reconstruction of posterior fossa by cranioplasty with use of preshaped titanium mesh following posterior fossa decompression (PFD) for Chiari malformation type I (CMI) with syringomyelia (SM) in symptomatic adults.

Materials and Methods:

Eleven patients underwent limited PFD and expansive cranioplasty with preshaped titanium mesh, what we term as “Stealth Cranioplasty” (SCP), following arachnoid preserving duraplasty (APD) and hexagonal tenting of the duraplasty with the cranioplasty (HTDC) for the management of symptomatic adult CMI with SM. All these patients had syringes extending from 3 to >10 vertebral levels.

Results:

Seven male and four female symptomatic CMI adult patients, between age ranges of 22 and 44 years (mean 29.45 years), presented with different neurological symptoms related to CMI and SM for 6–84 months (mean 37.09 months). All the patients underwent PFD, APD followed by SCP and HTDC and were followed up for 7–54 months (mean 35.90 months). Of 11 patients, 8 patients improved according to the Chicago Chiari Outcome Scale (CCOS) with score of 13–15 while 3 patients remained unchanged with CCOS of 12, and there was no worsening. There was no complication related to Chiari surgery in any of the patients. All the patients had good reestablishment of cisterna magna. Two patients had marked reduction of syrinx while eight patients had moderate-to-mild reduction and one patient had no change of syrinx. None of the patients needed redo surgery.

Conclusion:

SCP is an effective, fruitful, and cost-effective technique for the management of symptomatic adult CMI with SM. This technique has the advantages of preventing complications and recurrences in addition to the improvement of symptoms by addressing the basic pathology.

The Association of Pseudohypoparathyroidism Type Ia with Chiari Malformation Type I: A Coincidence or a Common Link?

A 19-month-old boy was referred for progressive weight gain. His past medical history included congenital hypothyroidism and developmental delay. Physical examination revealed characteristics of Albright Hereditary Osteodystrophy, macrocephaly, and calcinosis cutis. He had hypocalcemia, hyperphosphatemia, and elevated Parathyroid Hormone levels. Genetic testing revealed a known mutation of GNAS gene, confirming the diagnosis of Pseudohypoparathyroidism Type Ia (PHP-Ia) (c.34C>T (p.G1n12X)). He had a normal brain MRI at three months, but developmental delay prompted a repeat MRI that revealed Chiari Malformation Type I (CM-I) with hydrocephalus requiring neurosurgical intervention. This was followed by improvement in attaining developmental milestones. Recently, he was diagnosed with growth hormone deficiency. This case suggests the potential association of CM-I with PHP-Ia. Larger studies are needed to assess whether CM-I with hydrocephalus are common associations with PHP-Ia and to define potential genetic links between these conditions. We propose a low threshold in performing brain MRI on PHP-1a patients, especially those with persistent developmental delay to rule out CM-I. Early intervention may improve neurodevelopmental outcomes and prevent neurosurgical emergencies.