Diffusion tensor imaging in pediatric Chiari type I malformation

Clinical Application of Diffusion Tensor Imaging in Chiari Malformation Type I- Advances and Perspectives. A Systematic Review

BACKGROUND

Diffusion tensor imaging (DTI) application in Chiari malformation type I (CMI) is still poorly defined. This study aimed to systematically review the literature and propose perspectives toward the clinical application of DTI in CMI.

METHODS

PubMed and Embase were searched for English-language articles published until October 20, 2020. Clinical studies and case series, evaluating fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), or radial diffusivity values in patients with CMI, were included.

RESULTS

Eight articles were included. Lower FA values were found at the syrinx level, which decreased with syrinx extent and intensity of symptoms, reflecting myelopathy severity. Decreased AD and MD in the middle cerebellar peduncles in symptomatic patients with CMI might explain the presence of cerebellar signs. Increased FA in various supratentorial structures positively correlated with pain severity. Worse performance in neuropsychological tests correlated with decreased FA, increased MD, and radial diffusivity, reflecting axonal degeneration. Postoperative FA decrease in the brainstem compression area reflects successful decompression. A positive correlation was found between the extent of tonsillar ectopia and increased FA, MD, and AD values, which could act as an early indicator of acute brainstem compression.

CONCLUSIONS

DTI might provide a valuable insight into the neurobiological foundation of symptomatic CMI presentation. The severity of white matter injury evident on DTI could serve as a reliable predictor of postoperative outcomes, therefore facilitating selection of appropriate surgical candidates. Postinterventional DTI reassessment might enable differentiation between unsuccessful surgical technique and irreversible myelopathy. The extent of tonsillar ectopia reflects the severity of microstructural brainstem injury.

The Perplexity Surrounding Chiari Malformations - Are We Any Wiser Now?

Chiari malformations are a diverse group of abnormalities of the brain, craniovertebral junction, and the spine. Chiari 0, I, and 1.5 malformations, likely a spectrum of the same malformation with increasing severity, are due to the inadequacy of the para-axial mesoderm, which leads to insufficient development of occipital somites. Chiari II malformation is possibly due to nonclosure of the caudal end of the neuropore, with similar pathogenesis in the rostral end, which causes a Chiari III malformation. There have been significant developments in the understanding of this complex entity owing to insights into the pathogenesis and advancements in imaging modalities and neurosurgical techniques. This article aims to review the different types and pathophysiology of the Chiari malformations, along with a description of the various associated abnormalities. We also highlight the role of ante- and postnatal imaging, with a focus on the newer techniques in the presurgical evaluation, with a brief mention of the surgical procedures and the associated postsurgical complications.

Chiari I malformation-neuropsychological functions and quality of life

OBJECTIVE

To assess the neuropsychological (NP) functioning and quality of life (QOL) before and 3 months after surgery on adults with Chiari I malformation (CMI).

PATIENTS AND METHODS

All adult patients who had been diagnosed with CMI were invited to participate. Those who participated were assessed using a Hospital Anxiety and Depression scale (HAD) and NP examinations. Their QOL was assessed using the self-reported life satisfaction checklist, LiSat-11 and the five-dimensional EuroQol measurement of health outcome, EQ-5D-5L. All assessments were carried out both before and 3 months after surgery was performed. Demographic data and comorbidities were also registered.

RESULTS

Of the 11 patients who underwent NP assessment, the majority demonstrated cognitive functioning within the normal range. However, postoperatively, their performance in verbal learning, psychomotor speed, colour naming speed and the ability to manage interference through response selection and inhibition (aspects of executive functioning) was significantly improved. Thirteen patients completed QOL assessments. When LiSat-11 item domains were compared with those of healthy subjects, patients reported a lower level of satisfaction with their life quality both before and after surgery. However, the EQ-5D-5L measurements, i.e., the descriptive system and the visual analogue, indicated that their QOL of life was significantly improved after surgery.

CONCLUSION

There is scarcely any literature documenting effects of surgery on the QOL of CMI patients. The study we present here breaks new ground by comparing pre- and postoperative NP functions in CMI. We also examine the value of surgery for improving both NP functions and QOL in CMI.

Clinical diagnosis-part II: what is attributed to Chiari I

PURPOSE

Chiari malformation type I is identified as radiological appearance of cerebellar tonsil herniation below the foramen magnum. The wide spectrum of clinical manifestations variably associated sometimes encompasses signs and symptoms whose correlation with the malformation remains debatable. However, a correct clinical framework is relevant in tailoring the strategy of management, and in particular, establishing the appropriate surgical intervention.

METHODS

An analysis of relevant articles on this issue was performed, involving both single case reports and case series. The papers were obtained from electronic databases including PubMed/MEDLINE and Google Scholar, as well as direct contact with some authors.

RESULTS

This review focuses on those unusual clinical pictures attributed to Chiari malformation type I (CMI), investigating their actual relationship with the morphological condition. Supposed physiopathogenetic mechanisms and clinical relevance are discussed along with an analysis on the surgical indications and results.

CONCLUSION

There is no clear explanation on why some patients may exhibit uncommon symptoms, often in association with the most frequent ones, but even reported as single initial clinical occurrence. Their actual incidence may have been roughly underestimated in the literature so far, because of wide heterogeneity of selection and analysis among different studies. Most of the authors appear sharing the impression that CMI surgical decompression plays a significant role in controlling the majority of these unusual symptoms, stressing their actual occurrence in relation with the malformation. A routinely multidisciplinary clinical approach has become advisable to encompass the diversity of conditions potentially associated with CMI and improve the care of CMI patients.

Which neuroimaging techniques are really needed in Chiari I? A short guide for radiologists and clinicians

PURPOSE

To describe the most appropriate techniques and suggested protocols meant to address the various scenarios that clinicians and pediatric neurosurgeons may face in their day-to-day practice connected with Chiari I.

METHODS

Current literature related to image indications and findings in Chiari I has been reviewed. The authors focused on both standard and advanced techniques for clinical diagnosis and preoperative planning purposes.

DISCUSSION AND CONCLUSION

The complexity of providing neuroimaging guidelines for children investigated for Chiari I lies in defining the most appropriate neuroradiology tool to approach what is in fact a very heterogeneous condition with different etiopathogenetic mechanisms and associated abnormalities. Other variables that may influence the diagnostic strategy include the age of the patient, the presence of additional pathological conditions, the type of presenting symptoms, and the indication for surgical or conservative management. Although the average age at time of diagnosis is 10 years, the initial diagnosis may be done at any age, and the referral for neuroradiology workup may come from general practitioners/pediatricians, orthopedic surgeons, and endocrinologists following various baseline investigations including plain x-rays of skull and spine and/or CT head and/or MRI brain and spine.

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.

Cognitive Functioning in Chiari Malformation Type I Without Posterior Fossa Surgery

Chiari Malformation type I (CM-I) is a neurological disorder characterized by a displacement of the cerebellar tonsils through the foramen magnum into the spinal canal. Most research has focused on physical symptomatology but few studies include neuropsychological examinations. Moreover, although current research highlights the involvement of the cerebellum on higher cognitive functions, little is known about cognitive consequences associated with CM-I. The aim of this study is to analyze cognitive functioning between 39 CM-I patients and 39 healthy controls, matched by gender, age and years of education. Participants have been examined on a large battery of neuropsychological tests, including executive functioning, verbal fluency, spatial cognition, language, verbal memory, processing speed, facial recognition and theory of mind. Results show a poorer performance of the clinical group compared to the control group, even after controlling the effect of physical pain and anxious-depressive symptomatology. The findings suggest the presence of a generalized cognitive deficit associated with CM-I, which makes it necessary to focus attention not only on physical consequences, but also on cognitive ones.

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.

Diffusion tensor imaging findings of the brainstem in subjects with tonsillar ectopia

We aimed to evaluate the differences between apparent diffusion coefficient (ADC), fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) values obtained from different cranial sites in subjects with Chiari I Malformation (CM-I) and borderline tonsillar ectopia (BTE), and to determine correlations between diffusion tensor imaging (DTI) metrics and the severity of tonsillar ectopia. A total of 73 subjects with CM-I and BTE and 35 control underwent MRI and DTI. In our study, ADC values measured from the level of medulla oblongata and the RD values measured in middle cerebellar peduncles, thalamus, and globus pallidus were higher in CM-I patients than in controls. FA values at the medulla oblongata level and AD values at the medulla oblongata and pons level higher in patients with CM-I. ADC and AD values measured at the pons level were higher in BTE subjects than in controls. Compared with BTE, the CM-I subjects' ADC values at the medulla oblongata and AD values at the pons level were higher. In addition, FAs at the pons and medulla oblongata level were higher. At the medulla oblongata level, a positive correlation was observed between ADC and the size of tonsillar ectopia. AD and FA values measured at the level of medulla oblongata and pons were positively correlated with the size of tonsillar ectopia. These findings may be related to the severity of microstructural changes involving neuronal tracts at the brainstem level due to tonsillar ectopia. DTI may be useful in determining the extent of microstructural changes at the tissue level in subjects with tonsillar ectopia.

Imaging of Congenital Malformations

PURPOSE OF REVIEW

Intracranial congenital malformations are anomalies of brain development caused by genetic and environmental influences. This article discusses common intracranial congenital malformations, presents the associated neuroimaging findings, and discusses how appropriate identification of intracranial anomalies can impact diagnosis and treatment.

RECENT FINDINGS

Advances in neuroimaging techniques and genetic research have led to a better understanding of the pathogenesis of many congenital malformations, adding insight into their clinical relevance and the intricate relationship between critical periods of development, genetic predisposition, and environmental insults. When one malformation is discovered, a high likelihood of more malformations exists. In some instances, the intracranial anomalies will lead to the diagnosis of a particular neurologic syndrome, which may, in turn, lead to modification of a plan of care.

SUMMARY

Knowledge of congenital malformations and their appearance on imaging sequences is essential to improve clinical outcomes and quality of life for patients.

Probing the neuroanatomy of the cerebellum using tractography

Diffusion tensor imaging (DTI) is a noninvasive neuroimaging tool assessing the organization of white-matter tracts and brain microstructure in vivo. The technique takes into account the three-dimensional (3D) direction of diffusion of water in space, the brownian movements of water being constrained by the brain microstructure. The main direction of diffusion in the brain is extracted to obtain the principal direction of axonal projection within a given voxel. Overall, the diffusion tensor is a mathematic analysis of the magnitude/directionality (anisotropy) of the movement of water molecules in 3D space. Tracts running in the white matter are subsequently reconstructed graphically with fiber tractography. Tractography can be applied to myelinated and unmyelinated fibers or axonopathy. Decreased fractional anisotropy in white-matter tracts occurs in cases of injury with disorganized or disrupted myelin sheaths. Furthermore, high angular resolution methods enable detection of fiber crossings or convergence. DTI is a modern tool which complements conventional magnetic resonance techniques and is particularly relevant to assess the organization of cerebellar tracts. Indeed, both the afferent and efferent pathways of the cerebellar circuitry passing through the inferior, middle, and superior cerebellar peduncles can be visualized in vivo, including in children. The microanatomy of the cerebellar cortex and cerebellar nuclei is also emerging as a future assessment. Applications in the field of cerebellar disorders are multiple, ranging from developmental disorders to adult-onset cerebellar ataxias.

Diffusion tensor imaging assessment of microstructural brainstem integrity in Chiari malformation Type I

OBJECTIVE The diagnosis of Chiari malformation Type I (CM-I) is primarily based on the degree of cerebellar tonsillar herniation even though it does not always correlate with symptoms. Neurological dysfunction in CM-I presumably results from brainstem compression. With the premise that conventional MRI does not reveal brain microstructural changes, this study examined both structural and microstructural neuroimaging metrics to distinguish patients with CM-I from age- and sex-matched healthy control subjects. METHODS Eight patients with CM-I and 16 controls were analyzed. Image postprocessing involved coregistration of anatomical T1-weighted with diffusion tensor images using 3D Slicer software. The structural parameters included volumes of the posterior fossa, fourth ventricle, and tentorial angle. Fractional anisotropy (FA) was calculated separately in the anterior and posterior compartments of the lower brainstem. RESULTS The mean age of patients in the CM-I cohort was 42.6 ± 10.4 years with mean tonsillar herniation of 12 mm (SD 0.7 mm). There were no significant differences in the posterior fossa volume (p = 0.06) or fourth ventricular volume between the 2 groups (p = 0.11). However, the FA in the anterior brainstem compartment was significantly higher in patients with CM-I preoperatively (p = 0.001). The FA values normalized after Chiari decompression except for persistently elevated FA in the posterior brainstem compartment in patients with CM-I and syrinx. CONCLUSIONS In this case-control study, microstructural alterations appear to be reliably associated with the diagnosis of CM-I, with a significantly elevated FA in the lower brainstem in patients with CM-I compared with controls. More importantly, the FA values normalized after decompressive surgery. These findings should be validated in future studies to determine the significance of diffusion tensor imaging-based assessment of brainstem microstructural integrity as an adjunct to the clinical assessment in patients with CM-I.

Parent-Reported Executive Dysfunction in Children and Adolescents with Chiari Malformation Type 1

BACKGROUND

Children with Chiari malformation type 1 (CM1) have increasingly presented to neurosurgery clinics. Limited research relating to the cognitive dysfunction experienced by this population has been completed. In adults, inhibition problems and executive dysfunction have been documented.

METHODS

Seventy-seven parental reports of children with CM1 were included in the study. Parents completed questions on a scale rating daily executive functioning as well as reporting on common neurological symptoms.

RESULTS

The sample consisted of 41 males and 36 females with a mean age of 133.57 ± 42.18 months. Thirty-eight subjects had had decompression surgery. The most common neurological symptoms included: headache (69%), a history of pain (31%) and gait disturbance (20%). One third of the sample demonstrated overall executive functioning impairment, with working memory elevations being most prevalent (44%). Depression, gender, age and decompression surgery were not related to executive dysfunction.

CONCLUSIONS

The parental report of executive dysfunction in children with CM1 was higher than the standardized healthy sample. Metacognitive problems, especially working memory and initiation problems were most prevalent. A quick parental rating scale identifying children with executive dysfunction may be beneficial for neurosurgeons and assist with referrals for a more comprehensive neuropsychological assessment.