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Measurement of CSF flow and brain motion in Chiari malformation type I subjects undergoing posterior fossa decompression surgery
Abstract
OBJECTIVE
Radiologically, Chiari malformation type I (CM-I) is characterized by cerebellar tonsil herniation of at least 5 mm through the foramen magnum. In symptomatic cases, posterior fossa decompression (PFD) surgery is often performed and improves symptoms in approximately 75% of patients. However, the surgery involves risks, and identifying which candidates will benefit from surgery is important. It has previously been shown that the amount of tonsillar descent does not correlate with symptom severity or surgical outcomes. The authors hypothesized that using advanced neuroimaging methods to directly measure CSF flow and brain motion will give insights regarding which patients have the greatest likelihood of cerebral dynamic improvements from surgery.
METHODS
Here, the authors evaluated 108 CM-I patients (age 19–70 years), 61 of whom underwent PFD surgery. The authors used phase-contrast MRI to measure CSF flow/stroke volume and cine displacement encoding with stimulated echoes (DENSE) imaging to measure brain motion, with a goal to predict postsurgical cerebral dynamic improvements from presurgical images.
RESULTS
The authors found that CSF stroke volume increased after PFD surgery by 28.9% (p = 0.014), brainstem motion decreased after surgery by 17.3% (p = 0.002), and cerebellum motion decreased 45.2% (p < 0.001). Notably, the amount of CSF flow increase after surgery had no relationship to tonsillar descent (R = 0.059, p = 0.767) but did relate to the amount of presurgical CSF flow (R = −0.518, p = 0.005). Likewise, improvements to brain motion were better predicted by the amount of presurgical motion (brainstem, R = −0.638, p < 0.001; cerebellum, R = −0.878, p < 0.001) than by tonsillar descent (brainstem, R = −0.312, p = 0.093; cerebellum, R = −0.620, p < 0.001).
CONCLUSIONS
Here, the authors found that presurgical measures of cerebral dynamics were more descriptive of improvements to CSF flow and brain motion after PFD surgery than the conventional measure of presurgical tonsillar descent. These expanded quantitative assessments to determine which patients may benefit from surgery could improve the overall quality of patient care.
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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.
Purpose
Chiari malformation is a group of congenital malformations involving the brainstem, cerebellum, and upper spinal cord, frequently identified in both young adults and in children. Chiari I malformation (CM1), classically defined as a caudal displacement of the cerebellar tonsils through the foramen magnum into the spinal cord, is the most common clinical type. A syringomyelia can be associated at the time of the diagnosis or appear secondarily and manifest with medullary symptoms. The aim of this paper is to update the knowledge on clinical manifestations specifically related to Chiari I malformation with or without syringomyelia in the pediatric population.
Methods
Current literature with focus on relevant clinical pediatric issues is reviewed and discussed, comparing with those related to adults; we include the results of a 10-year single-center experience on 600 CM1 patients.
Results and conclusions
Herniation of the cerebellar tonsils may lead to significant clinical symptoms, including neck and cervical pain, short-lasting occipital “cough” headache, dizziness, and gait impairment; in children younger than 3 years, oropharyngeal symptoms are prevalent (sleep apnea, feeding problems) whereas in those older than 3 years, a higher incidence of cough headache and scoliosis is reported. CM1 clinical features, both in children and in adults, have in common the presence of anatomical deformities of the brainstem and cerebellum. Clinical myelopathy (sensory/autonomic disorders, motor weakness) can result from direct compression of the cervical spinal cord by the herniated cerebellar tonsils or can be due to the presence of a syrinx, reported in association with Chiari I between 35 and 75% of pediatric patients. Similarly, in our series (440 females, 160 males, 98% > 18 years), syringomyelia associated with Chiari I was ranging from 40 to 60% (respectively in asymptomatic and symptomatic groups); headache was reported in 65%. Sensory disturbances (48%), cranial nerve deficits (45%), motor weakness (32%), and autonomic disorders (35%) were the most frequent neurological signs in our cohort. In Chiari I malformation, cervical pain and occipital cough headache are the most characteristic presenting symptoms, both in old children and in adults; however, headache is often multifactorial, and CM1 patients can report a wide variety of non-specific symptoms and signs. Clinical diagnostic CM1 criteria, shared at the national and international level, are recommended with the aim to avoid consequent controversies on diagnosis and on surgical decision making.
Brain tissue undergoes viscoelastic deformation and volumetric strain as it expands over the cardiac cycle due to blood volume changes within the underlying microvasculature. Volumetric strain measurements may therefore provide insights into small vessel function and tissue viscoelastic properties. Displacement encoding via stimulated echoes (DENSE) is an MRI technique that can quantify the submillimetre displacements associated with brain tissue motion. Despite previous studies reporting brain tissue displacements using DENSE and other MRI techniques, a complete picture of brain tissue volumetric strain over the cardiac cycle has not yet been obtained. To address this need we implemented 3D cine‐DENSE at 7 T and 3 T to investigate the feasibility of measuring cardiac‐induced volumetric strain as a marker for small vessel blood volume changes. Volumetric strain over the entire cardiac cycle was computed for the whole brain and for grey and white matter tissue separately in six healthy human subjects. Signal‐to‐noise ratio (SNR) measurements were used to determine the voxel‐wise volumetric strain noise. Mean peak whole brain volumetric strain at 7 T (mean ± SD) was (4.5 ± 1.0) × 10⁻⁴ (corresponding to a volume expansion of 0.48 ± 0.1 mL), which is in agreement with literature values for cerebrospinal fluid that is displaced into the spinal canal to maintain a stable intracranial pressure. The peak volumetric strain ratio of grey to white matter was 4.4 ± 2.8, reflecting blood volume and tissue stiffness differences between these tissue types. The mean peak volumetric strains of grey and white matter tissue were found to be significantly different (p < 0.001). The mean SNR at 7 T and 3 T of the DENSE measurements was 22.0 ± 7.3 and 7.0 ± 2.8 respectively, which currently limits a voxel‐wise strain analysis at both field strengths. We demonstrate that tissue specific quantification of volumetric strain is feasible with DENSE. This metric holds potential for studying blood volume pulsations in the ageing brain in healthy and diseased states.
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.
Objective:
Chiari type 1 malformations (CM-1) are variations of hind-brain development which can sometimes occur in asymptomatic individuals. Conventional treatment is surgical decompression, but little is known about the natural history of patients who do not undergo surgical management. Appreciation of this information is critical to determine how these patients should be managed. We conducted a systematic review of the literature to determine the natural history of CM-1 particularly in patients who did not undergo surgery, and in asymptomatic individuals, to help inform patients and doctors when surgery is likely to be beneficial.
Methods:
A systematic literature search was performed following PRISMA guidelines using the electronic databases PubMed, SCOPUS, the Cochrane foundation and Web of Science. Inclusion and exclusion criteria were predefined.
Results:
In symptomatic patients who did not undergo surgery, headaches and nausea often improved, whereas ataxia and sensory disturbance tended not to improve spontaneously. 27-47% had an improvement in their symptoms after 15 months. 37-40% of patients with cough headache and 89% with nausea who were managed non-operatively improved at follow up. Most asymptomatic individuals with CM-1 remained asymptomatic (93.3%), even in the presence of syringomyelia.
Conclusions:
The natural history of mild symptomatic and asymptomatic CM-1 in adults is relatively benign and non-progressive, therefore the decision to perform surgical decompression should be based on the severity and duration of a patient's symptoms at presentation. It is reasonable to observe a patient with mild or asymptomatic symptoms, even in the presence of significant tonsillar descent or syringomyelia.
For 200 years, the ‘closed box’ analogy of intracranial pressure (ICP) has underpinned neurosurgery and neuro-critical care. Cushing conceptualised the Monro-Kellie doctrine stating that a change in blood, brain or CSF volume resulted in reciprocal changes in one or both of the other two. When not possible, attempts to increase a volume further increase ICP. On this doctrine’s “truth or relative untruth” depends many of the critical procedures in the surgery of the central nervous system. However, each volume component may not deserve the equal weighting this static concept implies. The slow production of CSF (0.35 ml/min) is dwarfed by the dynamic blood in and outflow (∼700 ml/min). Neuro-critical care practice focusing on arterial and ICP regulation has been questioned. Failure of venous efferent flow to precisely match arterial afferent flow will yield immediate and dramatic changes in intracranial blood volume and pressure. Interpreting ICP without interrogating its core drivers may be misleading. Multiple clinical conditions and the cerebral effects of altitude and microgravity relate to imbalances in this dynamic rather than ICP per se. This article reviews the Monro-Kellie doctrine, categorises venous outflow limitation conditions, relates physiological mechanisms to clinical conditions and suggests specific management options.
In this review, a companion piece to our recent examination of choroid plexus (CP), the organ that secretes the cerebrospinal fluid (CSF), we focus on recent information in the context of reliable older data concerning the composition and functions of adult human CSF. To accomplish this, we define CSF, examine the methodology employed in studying the CSF focusing on ideal or near ideal experiments and discuss the pros and cons of several widely used analogical descriptions of the CSF including: the CSF as the "third circulation," the CSF as a "nourishing liquor," the similarities of the CSF/choroid plexus to the glomerular filtrate/ kidney and finally the CSF circulation as part of the "glymphatic system." We also consider the close interrelationship between the CSF and extracellular space of brain through gap junctions and the paucity of data suggesting that the cerebral capillaries secrete a CSF-like fluid. Recently human CSF has been shown to be in dynamic flux with heart-beat, posture and especially respiration. Functionally, the CSF provides buoyancy, nourishment (e.g., vitamins) and endogenous waste product removal for brain by bulk flow into the venous (arachnoid villi and nerve roots) and lymphatic (nasal) systems, and by carrier-mediated reabsorptive transport systems in CP. The CSF also presents many exogenous compounds to CP for metabolism or removal, indirectly cleansing the extracellular space of brain (e.g., of xenobiotics like penicillin). The CSF also carries hormones (e.g., leptin) from blood via CP or synthesized in CP (e.g., IGF-2) to brain. In summary the CP/CSF, the third circulation, performs many functions comparable to the kidney including nourishing the brain and contributing to a stable internal milieu for brain. These tasks are essential to normal adult brain functioning.
Copyright © 2015. Published by Elsevier Inc.
Chiari malformations (CMs) constitute a variety of four mainly syndromes (I, II, III, and IV), which describe the protrusion of brain tissue into the spinal canal through the foramen magnum. These malformations frequently occur in combination with other pathological entities such as myelomeningocele, hydrocephalus, and/or hydrosyringomyelia. The recent improvement of imaging techniques has increased not only the rate of CM diagnosis but also the necessity for its early treatment. Several different surgical techniques have been employed in the treatment of patients with symptomatic CM-I. In our current study, a systematic and critical review of the pertinent literature was made for identifying the most commonly employed surgical procedures in the management of these patients. Emphasis was given in outlining the advantages and disadvantages of each surgical approach. Moreover, an attempt was made for defining those parameters that may be prognostic factors for their surgical outcome. There is a consensus that surgical treatment is reserved only for symptomatic patients with CM-I. It has also been postulated that early surgically intervention is usually associated with better outcome. Despite the large number of previously published clinical series, further clinical research with large-scale studies is necessary for defining surgical treatment guidelines in these patients.
The objective of this study was to review past studies that have used engineering analysis to examine cerebrospinal fluid hydrodynamics in cranial and spinal subarachnoid spaces in both healthy humans and those affected by type I Chiari malformation.
A PubMed search of literature pertaining to cerebrospinal fluid hydrodynamics was performed with a particular focus on those that utilized methods such as computational fluid dynamics or experimental flow modeling.
From the engineer's perspective, type I Chiari malformation is an abnormal geometry of the cerebellum that causes increased resistance to cerebrospinal fluid flow between the intracranial and spinal subarachnoid space. As such, understanding the hydrodynamics of cerebrospinal fluid in the craniospinal subarachnoid space has long been thought to be important in the diagnosis and management of type I Chiari malformation. Hydrodynamic quantification of cerebrospinal fluid motion in the subarachnoid space may better reflect the pathophysiology of the disorder and serve as a prognostic indicator in conjunction with geometric magnetic resonance measurements that are currently used clinically. This review discusses the results of studies that have sought to quantify the hydrodynamics of cerebrospinal fluid motion using computational and experimental modeling and critiques the methods by which the results were obtained.
Researchers have found differences in cerebrospinal fluid velocities and pressures in type I Chiari malformation patients compared to healthy subjects. However, further research is necessary to determine the causal relationship between changes to hydrodynamic parameters such as cerebrospinal fluid velocity, pressure, resistance to flow, and craniospinal compliance and clinical aspects such as neurological symptoms, radiological evidence of severity, and surgical success.
Abnormal flow of CSF through the foramen magnum has been implicated in the pathogenesis of clinical deficits in association with Chiari I malformation. The purpose of this study was to test the hypothesis that peak CSF velocities in the foramen magnum are increased in patients with Chiari I malformations.
Eight adult patients with symptomatic Chiari I malformations and 10 adult volunteers were studied with cardiac gated, phase-contrast MR imaging in the axial plane at the foramen magnum. The spatial uniformity of flow velocity in the foramen magnum was assessed at 14 time frames within the R-R interval. The velocity in each of the voxels at each of the time frames was calculated, and the peak systolic and diastolic velocities were tabulated for the patients and controls.
For the normal volunteers, the CSF velocities in the subarachnoid space were relatively uniform throughout the subarachnoid space at each of the time frames. Peak systolic velocity ranged from 1.2 to 3.3 cm/s, and peak diastolic velocity ranged from 1.6 to 4.5 cm/s. In symptomatic patients with Chiari I, velocities in the foramen magnum did not appear as uniform throughout the subarachnoid space in the phase-contrast images. Peak systolic velocities ranged from 1.8 to 4.8 cm/s, and peak diastolic velocities ranged from 2.5 to 5.3 cm/s. Peak systolic velocity was significantly higher (P =.01) in the patients than in the control volunteers.
Patients with Chiari I malformations have significant elevations of peak systolic velocity in the CSF in the foramen magnum.
Since the introduction of MRI, the incidence of Chiari I malformations (cerebellar tonsils ectopia) has increased. The clinical significance of this finding remains questionable in some instances. Recently, cine flow MRI has added to the understanding of the dynamics of cerebrospinal fluid at the craniocervical junction and to the pathophysiology of the Chiari I malformation. The present study attempts to analyze the role of cine flow MRI in Chiari I malformations.
Between January 1990 and December 2000, 24 patients were identified who met the following inclusion criteria: patients diagnosed with Chiari I malformation who had had an MRI of the brain including the craniocervical junction, clinical follow-up for at least six months, and cine flow studies had to have been performed pre- and postoperatively. The cine flow studies were repeated during follow-up if the patients were not surgical candidates. Patients harboring intracranial space occupying lesions or lumboperitoneal shunts were excluded. Sixteen of the 24 selected patients underwent 18 operations and 8 were followed conservatively. There was a wide variation in clinical presentations. Twelve patients had cerebellar tonsils protruding more than 5 mm below the foramen magnum, and in 12 patients the descent of the cerebellar tonsils was less than 5 mm. Despite this difference in the degree of protrusion, there was no significant difference in clinical presentation. The cisterna magna was small or absent in 20 patients with sluggish cine flow posteriorly, 19 of whom were symptomatic, in contrast to 1 symptomatic patient who had satisfactory cine flow.
All patients with Chiari I malformation and an associated cervical syrinx had absent cine flow at the craniovertebral junction, and this finding was statistically significant. There was a good correlation between the clinical presentation and cine flow preoperatively, and between clinical improvement and cine flow postoperatively. Patients with Chiari I malformation, cervical syrinx, and absent cine flow preoperatively improved after suboccipital decompression and duroplasty. Patients with Chiari I malformations without syrinx and absent cine flow underwent suboccipital bony decompression alone and had satisfactory outcomes.
The aim of this prospective study was to define the role of cardiac gated phase-contrast ciné magnetic resonance imaging in deciding the therapeutic strategy in patients with Chiari I malformation.
Twenty-one patients operated on between February 2000 and July 2002 were enrolled in the study. All patients underwent a detailed preoperative neurological examination. MRI of the craniovertebral junction and the whole spine was done, followed by cardiac gated phase contrast ciné magnetic resonance imaging.
Signs and symptoms of syringomyelia were noted in 15 patients and cerebellar signs in 11 patients. Three of them had trigeminal nerve involvement, and 4 had ninth and tenth cranial nerve involvement. The sixth and accessory nerves were involved in 1 patient each. Preoperative CSF flow studies revealed obstructive flow both anteriorly and posteriorly in 6 patients and only posterior block in 15 patients. One patient investigated for failed foramen magnum decompression revealed obstruction to CSF flow ventrally. Foramen magnum decompression with duroplasty was done in all these cases. The patient who had a persistent ventral flow block underwent odontoidectomy. Patients were followed up for a maximum of 36 months, with a mean of 18 months. MRI CSF flow studies revealed established flow dorsally in all cases. Seventeen patients showed clinical improvement and 2 of them did not show any neurological changes. Two patients deteriorated following an initial period with a shunt.
MRI CSF flow study is an effective tool for deciding the type of surgery to be performed and also for monitoring patients postoperatively.
To measure spatial and temporal variations in cerebrospinal fluid (CSF) flow through the cardiac cycle and throughout the subarachnoid space at magnetic resonance (MR) imaging in volunteer subjects with no known neurologic or spinal problems and in patients with Chiari I malformation.
A cardiac-gated phase-contrast MR technique was used to acquire images at 14 time points evenly spaced through the cardiac cycle in 10 volunteers and eight patients with Chiari I malformation. Instantaneous CSF velocities were displayed as temporal and spatial plots and examined for homogeneity, differences between flow anterior and flow posterior to the spinal cord, synchronous bidirectional flow, and equivalence of the caudad flow and craniad flow in each voxel. Indexes for flow homogeneity, synchronous bidirectional flow, and preferential flow direction were calculated, and differences between the patient and volunteer groups were tested for significance with a t test of the means.
In volunteers, diastolic velocity peaked in two regions in the anterior paramedial subarachnoid space. Patients had greater inhomogeneity of flow than volunteers. They had substantially increased flow (jets) in the anterior paramedial locations. Synchronous bidirectional flow was seen in six of the patients and in none of the volunteers. Cephalad flow in the jets or nodes (P =.05), proportion of cephalad and caudad flow in the anterior compartment (P <.005 for both), and the fraction of voxels with flow directionality (P =.03) differed significantly between patients and volunteers.
CSF flow in symptomatic patients with Chiari I malformation, unlike that in volunteer subjects, is characterized by flow jets, regions with a preponderance of flow in one direction, and synchronous bidirectional flow.
Cranio‐spinal volume and pressure changes associated with the cardiac‐cycle and respiration are altered in Chiari I malformation (CMI) due to obstruction of cerebrospinal fluid (CSF) flow at the foramen magnum. With the introduction of motion‐sensitive MRI sequences, it was envisioned that these could provide noninvasive information about volume–pressure dynamics at the cranio‐cervical junction in CMI hitherto available only through invasive pressure measurements. Since the early 1990s, multiple studies have assessed CSF flow and brain motion in CMI. However, differences in design and varied approaches in the presentation of results and conclusions makes it difficult to fully comprehend the role of MR imaging of CSF flow and brain motion in CMI. In this review, a cohesive summary of the current status of MRI assessment of CSF flow and brain motion in CMI is presented. Simplified versions of the results and conclusions of previous studies are presented by dividing the studies in distinct topics: 1) comparing CSF flow and brain motion between healthy subjects (HS) and CMI patients (before and after surgery), 2) comparing CSF flow and brain motion to CMI severity and symptoms, and 3) comparing CSF flow and brain motion in CMI with and without syringomyelia. Finally, we will discuss our vision of the future directions of MR imaging in CMI patients.
Evidence Level
2.
Technical Efficacy
5.
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.
Objective:
The pathogenesis of Chiari malformation type 1 (CM-1) associated Valsalva headache is unknown, but may be caused by abnormal cerebellar tonsil tissue strain. Advances in cardiac-gated MRI techniques such as balanced fast field echo (bFFE) allow quantification of the motion of anatomical 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 symptomatology was retrieved from the medical records. Anatomical landmarks were manually selected on the cine bFFE and a validated motion-tracking software used to assess motion over the cardiac cycle in patients at rest. For each patient, displacement, strain and strain rate were calculated for three anatomical segments. Patients undergoing surgery were examined before and after surgery.
Results:
From 88 patients a total of 108 bFFE sequences were analysed. Valslava headache was present in 50% of patients. Cerebellar tonsil displacement (p= 0.003), strain (p = 0.012) and maximum strain rate (p = 0.04) reduced after surgery (n=20). There was no statistically significant association between tissue motion and headache symptomatology.
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 as it represents a potential biomarker for outcomes following surgery.
Objectives:
To test the hypothesis that two-dimensional (2D) displacement encoding via stimulated echoes (DENSE) is a reproducible technique for the depiction of segmental myocardial motion in human subjects.
Materials and methods:
Following the approval of the institutional review board (IRB), 17 healthy volunteers without documented history of cardiovascular disease were recruited. For each participant, 2D DENSE were performed twice (at different days) and the images were obtained at basal, midventricular and apical levels of the left ventricle (LV) with a short-axis view. The radial thickening strain (Err), circumferential strain (Ecc), twist and torsion were calculated. The intra-, inter-observer and inter-study variations of DENSE-derived myocardial motion indices were evaluated using coefficient of variation (CoV) and intra-class correlation coefficient (ICC).
Results:
In total, there are 272 pairs of myocardial segments (data points) for comparison. There is good intra- and inter-observer reproducibility for all DENSE-derived measures in 17 participants. There is good inter-study reproducibility for peak Ecc (CoV=19.64%, ICC=0.8896, p<0.001), twist (CoV=33.11%, ICC=0.9135, p<0.001) and torsion (CoV=13.96%, ICC=0.8684, p<0.001). There is moderate inter-study reproducibility for Err (CoV=38.89%, ICC=0.7022, p<0.001).
Conclusion:
DENSE is a reproducible technique for characterizing LV regional systolic myocardial motion on a per-segment basis in healthy volunteers.
OBJECTIVE
The pathogenesis of syringomyelia associated with Chiari malformation type I (CM-I) is unclear. Theories of pathogenesis suggest the cerebellar tonsils may obstruct CSF flow or alter pressure gradients, or their motion might act as a piston to increase CSF pressure in the spinal subarachnoid space. This study was performed to measure cerebellar tonsillar and hindbrain motion in CM-I and assess the potential contributions to syrinx formation.
METHODS
Sixty-four CM-I patients and 25 controls were retrospectively selected from a clinical database, and all subjects had undergone cardiac-gated cine balanced fast-field echo MRI. There were a total of 36 preoperative CM-I scans, which consisted of 15 patients with and 21 patients without syringomyelia. Nineteen patients underwent paired pre- and postoperative imaging. Anteroposterior (AP) and superoinferior (SI) movements of the tip of the cerebellar tonsils, obex, fastigium of the fourth ventricle, pontomedullary junction, and cervicomedullary junction were measured. The distance between the fastigium and tip of the tonsils was used to calculate tonsillar tissue strain (Δ i / i 0 ).
RESULTS
CM-I patients had significantly greater cerebellar tonsillar motion in both the AP and SI directions than controls (AP +0.34 mm [+136%], p < 0.001; SI +0.49 mm [+163%], p < 0.001). This motion decreased after posterior fossa decompression (AP −0.20 mm [−33%], p = 0.001; SI −0.29 mm [−36%]; p < 0.001), but remained elevated above control levels (AP +56%, p = 0.021; SI +67%, p = 0.015). Similar trends were seen for all other tracked landmarks. There were no significant differences in the magnitude or timing of motion throughout the hindbrain between CM-I patients with and without syringomyelia. Increased tonsillar tissue strain correlated with Valsalva headaches (p = 0.03).
CONCLUSIONS
Cerebellar tonsillar motion may be a potential marker of CM-I and may have use in tailoring surgical procedures. The lack of association with syringomyelia suggests that tonsillar motion alone is not the driver of syrinx formation. Tonsillar tissue strain may play a part in the pathophysiology of Valsalva headaches.
Few studies have directly compared operative and non-operative outcomes in Chiari I patients. We evaluated risk factors for clinical improvement in 177 patients in order to help determine the optimal treatment of these often difficult to treat patients. The mean age at surgery for the operative treatment group was 29.9years. The most common presenting signs and symptoms included cough headache (63.0%), migraine and non-cough type headaches (23.9%), paresthesias (32.1%), and abnormal reflexes or clonus (27.5%). The mean age of diagnosis for the non-operative treatment group was 30.2years. The most common presenting signs or symptoms included migraine and other types of non-cough-associated headache (57.4%), paresthesias (45.6%), cough headache (44.1%), cerebellar signs or symptoms (41.2%), and dysphagia or apnea (15.7%). A propensity score was generated using cough headache, any headache, other headache, syrinx, abnormal reflexes or clonus, cerebellar symptoms, and miscellaneous symptoms as independent predictors of selection for surgery. The propensity score-adjusted odds of overall improvement for patients treated with surgery were 16.5 times the odds of overall improvement for patients treated conservatively (95% confidence interval 5.5-57.1, p<0.0001). Overall 94.5% and 47.1% of operative and conservatively treated patients reported improvement, respectively. Only 26.5% of conservatively treated patients reported worsening of any of their symptoms. In conclusion, we provided further evidence for the use of cough headache as surgical indication for suboccipital decompression in patients with Chiari I malformation.
Chiari type I malformation is found in 1 out of 20 magnetic resonance imaging (MRI) studies. Isolated tonsillar herniation is of limited utility and should be considered within the clinical context because these patients can be asymptomatic. Cine MRI showing compression of the cerebrospinal fluid (CSF) spaces in the foramen magnum area is a crucial technique for making treatment decisions. Congenital malformation is thought to be due to a volumetric small posterior fossa. The most common symptom in these patients is cough headache. Posterior fossa reconstruction is mandatory in patients with progressive symptoms/signs, hydrocephalus, or syringomyelia, but not in patients who are asymptomatic or those with stable and tolerable symptoms. Acquired tonsillar descent can be secondary to a variety of disorders conditioning disproportion between the volume of the cranial cavity and that of the intracranial contents, or to CSF hypovolemia, which is the most common cause for acquired herniation. CSF hypovolemia can be spontaneous or secondary to CSF removal. Treatment of acquired tonsillar herniation depends on the responsible etiology.
A navigator-gated 3D spiral cine displacement encoding with stimulated echoes (DENSE) pulse sequence for imaging 3D myocardial mechanics was developed. In addition, previously described 2D postprocessing algorithms including phase unwrapping, tissue tracking, and strain tensor calculation for the left ventricle (LV) were extended to 3D. These 3D methods were evaluated in five healthy volunteers, using 2D cine DENSE and historical 3D myocardial tagging as reference standards. With an average scan time of 20.5 ± 5.7 min, 3D data sets with a matrix size of 128 × 128 × 22, voxel size of 2.8 × 2.8 × 5.0 mm(3), and temporal resolution of 32 msec were obtained with displacement encoding in three orthogonal directions. Mean values for end-systolic mid-ventricular mid-wall radial, circumferential, and longitudinal strain were 0.33 ± 0.10, -0.17 ± 0.02, and -0.16 ± 0.02, respectively. Transmural strain gradients were detected in the radial and circumferential directions, reflecting high spatial resolution. Good agreement by linear correlation and Bland-Altman analysis was achieved when comparing normal strains measured by 2D and 3D cine DENSE. Also, the 3D strains, twist, and torsion results obtained by 3D cine DENSE were in good agreement with historical values measured by 3D myocardial tagging.
The authors reviewed the postoperative alteration of symptoms and syrinx size by magnetic resonance imaging (MRI) in 14 consecutive patients with syringomyelia associated with Chiari malformation. The patients were treated according to our treatment regimen and were divided into five groups according to operative modalities: (1) only foramen magnum decompression (D) for small syrinx; (2) D with ventriculoperitoneal (VP) shunt for small syrinx with hydrocephalus; (3) D with syringosubarachnoid (SS) shunt or (4) D with syringoperitoneal (SP) shunt for large syrinx; and (5) only VP shunt for syrinx with hydrocephalus and atlantoaxial dislocation, respectively. From the preoperative and postoperative sagittal MR images, the areas of the spinal cord and syrinx were measured by a digitizer and the syringo-cord (S-C) ratio was calculated. Out of 14 patients, 12 showed a reduction of syrinx size and a stabilization or improvement of symptoms after surgery. In the other two patients, the syrinx size did not change and their symptoms worsened. Magnetic resonance imaging follow-up showed that foramen magnum decompression without shunt is effective for patients with a small syrinx below 35% of the S-C ratio, and foramen magnum decompression with shunt was effective for patients with a large syrinx over 35% of the S-C ratio, but there was no significant difference between the SS and SP shunt group.
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.
A breath-hold two-dimensional cine magnetic resonance (MR) pulse sequence based on displacement encoding with stimulated echoes (DENSE) for quantitative myocardial motion tracking was developed and evaluated. In the sequence, complementary spatial modulation of magnetization was used for time-independent artifact suppression, and echo-planar imaging was used for rapid data sampling. Twelve healthy volunteers underwent cine DENSE MR imaging, and six of them also underwent conventional MR imaging myocardial tagging. The circumferential shortening component of strain (E(cc)) was measured on cine DENSE MR images and conventional tagged MR images. With complementary spatial modulation of magnetization, 10% or less of the total cine DENSE MR image energy was attributed to an artifact-generating echo during systolic imaging. Two-dimensional intramyocardial displacement and strain were measured at cine DENSE MR imaging with spatial resolution and temporal resolution of 2.7 x 2.7 mm and 60 msec, respectively. E(cc) measured at cine DENSE MR imaging correlated well with that measured at conventional MR imaging tagging (slope = 0.88, intercept = 0.00, R = 0.87).
With the widespread use of newer neuroimaging techniques and modalities, significant tonsillar herniation is being diagnosed in more than 0.5% of patients, some of whom are asymptomatic. This puts the definition of the adult Chiari malformation to the test. The author provides a historical review of the evolution of the definition of the adult Chiari malformation in the neurosurgery, radiology, and pathology literature.
In displacement-encoded imaging with stimulated echoes (DENSE), tissue displacement is encoded in the phase of the stimulated echo. However, three echoes generally contribute to the acquired signal (the stimulated echo, the complex conjugate of the stimulated echo, and an echo due to T(1) relaxation). It is usually desirable to suppress all except the stimulated echo, since otherwise the additional echoes will cause displacement measurement errors. Ideally, suppression of the artifact-generating echoes would be independent of time, T(1), and displacement-encoding frequency, and would not require additional acquisitions. In this study through-plane gradients were used to selectively dephase artifact-generating echoes without causing significant signal loss of the stimulated echo. A cine DENSE sequence was modified to include dephasing gradients and perform complementary spatial modulation of magnetization (CSPAMM). For single-acquisition cine DENSE using dephasing alone, artifact suppression was similar to CSPAMM with two acquisitions. The use of dephasing with CSPAMM required two acquisitions, but demonstrated greater artifact suppression than CSPAMM alone or dephasing alone.
Surgery for Chiari malformation Type I (CM-I) is one of the most common neurosurgical procedures performed in children, although there is clearly no consensus among practitioners about which surgical method is preferred. The objective of this meta-analysis was to compare the outcome of posterior fossa decompression with duraplasty (PFDD) and posterior fossa decompression without duraplasty (PFD) for the treatment of CM-I in children.
The authors searched Medline-Ovid, The Cochrane Library, and the conference proceedings of the American Association of Neurological Surgeons and the Congress of Neurological Surgeons (2000-2007) for studies meeting the following inclusion criteria: 1) surgical treatment of CM-I; 2) surgical techniques of PFD and PFDD being reported in a single cohort; and 3) patient age < 18 years.
Five retrospective and 2 prospective cohort studies involving a total of 582 patients met the criteria for inclusion in the meta-analysis. Of the 582 patients, 316 were treated with PFDD and 266 were treated with PFD alone. Patient age ranged from 6 months to 18 years. Patients undergoing PFDD had a significantly lower reoperation rate (2.1 vs 12.6%, risk ratio [RR] 0.23, 95% confidence interval [CI] 0.08-0.69) and a higher rate of cerebrospinal fluid-related complications (18.5 vs 1.8%, RR 7.64, 95% CI 2.53-23.09) than those undergoing PFD. No significant differences in either clinical improvement (78.6 vs 64.6%, RR 1.23, 95% CI 0.95-1.59) or syringomyelia decrease (87.0 vs 56.3%, RR 1.43, 95% CI 0.91-2.25) were noted between PFDD and PFD.
Posterior fossa decompression with duraplasty is associated with a lower risk of reoperation than PFD but a greater risk for cerebrospinal fluid-related complications. There was no significant difference between the 2 operative techniques with respect to clinical improvement or decrease in syringomyelia.
Tracking brain motion during the cardiac cycle using spiral cine-DENSE MRI
- X Zhong
- C H Meyer
- D J Schlesinger
- Zhong X
Cerebellar and brainstem displacement measured with DENSE MRI in Chiari malformation following posterior fossa decompression surgery
- M S Eppelheimer
- Bst Nwotchouang
- Eppelheimer MS
Accurate posterior fossa decompression technique for Chiari malformation Type I and a syringomyelia with navigation: a technical note
- M Tanaka
- S Sharma
- Y Fujiwara
- Tanaka M
Chiari malformation in craniosynostosis
- G Cinalli
- P Spennato
- C Sainte-Rose
- Cinalli G