Diffusion tensor imaging in cervical syringomyelia secondary to Chiari I malformation: preliminary results

Potential impairment of spinal cord around the apical vertebral level in hyperkyphotic patients: findings from diffusion tensor imaging

PURPOSE

To evaluate the neuronal metrics/microstructure of the spinal cord around apical region in patients with hyperkyphosis using diffusion tensor imaging (DTI).

METHODS

Thirty-seven patients with hyperkyphosis aged 45.5 ± 19.6 years old who underwent 3.0 T magnetic resonance imaging (MRI) examination with DTI sequence were prospectively enrolled from July 2022 to July 2023. Patients were divided into three groups according to spinal cord/ cerebrospinal fluid (CSF) architecture on sagittal-T2 MRI of the thoracic apex (the axial spinal cord classification): Group A-circular cord with visible CSF, Group B-circular cord without visible CSF at apical dorsal, and Group C-spinal cord deformed without intervening CSF. The fractional anisotropy (FA) values acquired from DTI were compared among different groups. Correlations between DTI parameters and global kyphosis (GK)/sagittal deformity angular ratio (sagittal DAR) were evaluated using Pearson correlation coefficients.

RESULTS

In all patients, FA values were significantly lower at apical level as compared with those at one level above or below the apex (0.548 ± 0.070 vs. 0.627 ± 0.056 versus 0.624 ± 0.039, P < 0.001). At the apical level, FA values were significantly lower in Group C than those in Group B (0.501 ± 0.052 vs. 0.598 ± 0.061, P < 0.001) and Group A (0.501 ± 0.052 vs. 0.597 ± 0.019, P < 0.001). Moreover, FA values were significantly lower in symptomatic group than those in non-symptomatic group (0.498 ± 0.049 v. 0.578 ± 0.065, P < 0.001). Pearson correlation analysis showed that GK (r2 = 0.3945, P < 0.001) and sagittal DAR (r2 = 0.3079, P < 0.001) were significantly correlation with FA values at apical level.

CONCLUSION

In patients with hyperkyphosis, the FA of spinal cord at apical level was associated with the neuronal metrics/microstructure of the spinal cord. Furthermore, the DTI parameter of FA at apical level was associated with GK and sagittal DAR.

LEVEL OF EVIDENCE: 4

Diffusion Tensor Imaging in Syringomyelia Secondary to Chiari Malformation in Cavalier King Charles Spaniel-A Preliminary Study

Syringomyelia secondary to Chiari-like malformation (so-called CM-SM syndrome) is a common disorder in Cavalier King Charles Spaniels (CKCS) that is diagnosed using standard structural MRI, though imaging findings often do not correlate with the severity of clinical symptoms. Diffusion tensor imaging (DTI) is a technique that defines subtle microstructural changes in the course of many brain and spinal cord diseases, that are not visible on standard MRI. The aim of the study was to identify the correlation between the presence of clinical symptoms and DTI parameters, such as apparent diffusion coefficient (ADC) and fractional anisotropy (FA) within the spinal cord in the course of CM-SM. Study subjects included 18 dogs, CKCS with MRI-confirmed SM (SM group), and 12 CKCS dogs without SM (non-SM group). The SM group was divided into SM-symptomatic group (n = 8) and SM-asymptomatic group, n = 10). All dogs underwent same clinical and neurological assessment followed by MRI examination. All MRI studies were performed on a 1.5T MRI scanner. The MRI spine protocol included: transverse and sagittal T2-weighted images followed by DTI performed in the sagittal plane. The measurements of FA and ADC values were performed manually using the region of interest (ROI) method at the level of three intervertebral discs between C1 and C4. Notable differences in age and body weight were found. No significant differences in FA and ADC values between the SM and non-SM groups were found, but between non-SM, SM-asymptomatic and SM-symptomatic groups significant differences were found in ADC values in all three ROIs and in FA values in ROI-1 and ROI-3. SM-symptomatic dogs compared to non-SM, showed decreased FA value in ROI-1 and ROI-3 also increased ADC value in ROI-1, ROI-2 and ROI-3. SM-symptomatic dogs compared to SM-asymptomatic showed also decreased FA value in ROI-1 and ROI-3, and also increased ADC value in ROI-1, ROI-2 and ROI-3. The results suggest that the values of DTI parameters correlate with the severity of clinical symptoms in the course of CM-SM in animals. The use of DTI evaluation of CM-SM patients carries a potential value as a clinically relevant protocol for an objective assessment of the spinal cord.

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.

Specific microstructural changes of the cervical spinal cord in syringomyelia estimated by diffusion tensor imaging

The microstructure of the spinal cord in syringomyelia has not been well studied. The aim of this study was to evaluate the microstructure of the cervical cord in patients with syringomyelia using diffusion tensor imaging (DTI) and to investigate the association between DTI parameters and the size of the syrinx cavity. Thirty patients with syringomyelia and 11 age-matched controls were included in this study. DTI and T1/T2-weighted MRI were used to estimate spinal microstructure. The patients were divided into a clinical symptom group (group A) and a non-clinical symptom group (group B) according to ASIA assessments. The fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values (mm²/s) were measured and compared between patients and controls. Correlation between FA/ADC and the size of the syrinx cavity was examined with a bivariate analysis. FA values were lower (P < 0.000) and ADC values were higher (P < 0.000) compared to the controls at the level of all syrinxes examined in patients with syringomyelia; both FA values and ADC values reached normal values either above or below the syrinx levels (all P > 0.05). FA values and ADC values at all cervical levels were not significantly different either in controls or outside of the syrinx (all P > 0.05). FA values of group A was significantly lower than those of group B (P < 0.000). There was a negative association between FA values and the size of syrinx cavity, and a positive association between ADC values and the size of syrinx cavity (FA: P < 0.05, ADC: P < 0.05). The microstructure of the cervical spinal cord is different across all patients with syringomyelia. DTI is a promising tool for estimating quantitative pathological characteristics that are not visible with general MRI.

Optimal acceleration factor for image acquisition in turbo spin echo: diffusion-weighted imaging with compressed sensing

In this study, the change in the image quality and apparent diffusion coefficient (ADC) with increase in the acceleration factor (AF) was analyzed and the most optimal AF was determined to reduce the scan time while preserving the image quality. The AF was changed from 2 to 20 in the MR acquisitions. The similarities between the accelerated and reference images were determined based on the structural similarity (SSIM) index for DWI image and coefficient of variation (%CV) for ADC. The SSIM index decreased significantly when the AF ≥ 8 compared with when the AF = 2 (p < 0.05). In the reference image, the %CV of the ADC increased significantly when the AF ≥ 10 (p < 0.01). In conclusion, a remarkable decrease in the image quality and ADC was observed when the AF was > 8. Thus, an AF < 8 would be optimal for reducing the scan time while preserving the image quality.

Syringomyelia Resolution Following Chiari Surgery: A Novel Scale for Communication and Research

BACKGROUND

The pathophysiological connection between Chiari malformation and syringomyelia is accepted. Debate remains, however, how can we best define changes in syringomyelia following surgery.

OBJECTIVE

To introduce a grading system focusing on syrinx reduction based on routinely and reproducible radiological information, and provide a suggestion of the application of this scale for prediction of patient's prognoses.

METHODS

Data from 48 patients with Chiari malformation and syringomyelia were compiled. We calculated syrinx cross-sectional area by approximating an ellipse in the largest axial plane. We compared the percentage of reduction or enlargement following surgery. The percentage change was grouped into four grades: Grade 0 = Increasing size, grade I ≤ 50% reduction, grade II = 50% to 90% reduction, grade III ≥ 90% reduction.

RESULTS

A total of 89.6% of patients had syrinx improvement after surgery. A total of 5 patients were grade 0, 14 were grade I, 20 patients were grade II, and 9 patients met criteria for grade III. The mean postoperative syrinx area was 24.1 mm2 (0-169 mm2) with a mean syrinx reduction of 62.7%.

CONCLUSION

Radiological improvement of syringomyelia can be mathematically defined and standardized to assist in communication in outcome-based trials. Radiological resolution is expected most patients.

Syringomyelia and hydromyelia: Current understanding and neurosurgical management

Syringomyelia is a rare disorder in which a fluid-filled cyst forms within the spinal cord, resulting in myelopathy. Meanwhile, the abnormal dilatation of the central canal is referred to as hydromyelia or slit-like syrinx. The most prevailing classification is based on anatomical features and pathogeny rather than pathophysiological mechanisms. It is usual to distinguish foraminal syringomyelia related mainly to abnormalities at the craniocervical junction, non-foraminal syringomyelia dealing with any cause of arachnoiditis (infection, inflammation, trauma…) and more rarely syringomyelia associated with intramedullary tumors. Although many pathophysiological theories have been argued over time, the prevailing one is that disturbances in cerebrospinal fluid (CSF) flow in the sub-arachnoid spaces disrupt flow velocity leading to the syrinx. Symptoms of paralysis, sensory loss and chronic pain commonly develop during the third/fourth decades of life. The natural history of syringomyelia is typically one of gradual, stepwise neurological deterioration extending over many years. Diagnosis is based on magnetic resonance imaging (MRI) including excellent morphological sequences (T1-, T2-, FLAIR-, T2*-, enhanced T1-) and dynamic MRI with careful study of CSF velocity (CISS, cine-MR sequences). Surgical management is at first dedicated to treat the cause of the syringomyelia, mainly to re-establish a physiological CSF pathway in the subarachnoid spaces. Mostly, the surgical goal is to enlarge the craniocervical junction with duraplasty. Other surgical strategies such as arachnoidolysis or shunt procedures are performed based on the pathogenic mechanisms or as second-line treatment. Medical treatments are also necessary as chronic pain is the main long-lasting symptom. As evolutive syringomyelia is a severe disease with a high impact on quality of life, it is recommended to treat without delay. There is no evidence for surgery for incidental asymptomatic syringomyelia or hydromyelia. Finally, syringomyelia associated with intramedullary tumors resolves spontaneously after tumor resection. Syringomyelia is a rare disease, which requires a dedicated multidisciplinary approach, emphasizing the need for a nationwide scientific organization so as to offer optimal care to the patient.

Somatosensory and motor evoked potentials during correction surgery of scoliosis in neurologically asymptomatic Chiari malformation-associated scoliosis: A comparison with idiopathic scoliosis

OBJECTIVES

To analyze the somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in neurologically asymptomatic Chiari malformation-associated scoliosis (CMS) patients with and without syringomyelia as compared with those in idiopathic scoliosis (IS) ones, and to identify whether the deformities have impacts on the neurophysiological monitoring.

PATIENTS AND METHODS

This study included neurologically asymptomatic CMS patients undergoing posterior correction surgery between January 2010 and January 2016. IS patients were involved as control group and a subgroup of age- and height-matched IS patients were selected. The age, standing height and Cobb angles of main curve were measured. The SEPs latency and amplitude, MEPs amplitude, and the rate of abnormal SEPs pathologic change were compared between CMS and IS patients using independent-sample t-test and Chi-square test.

RESULTS

Sixty CMS patients and 210 IS patients were included. There was no difference between CMS patients and IS or matched IS patients in SEPs latency and amplitude, MEPs amplitude or rate of abnormal SEPs (p > 0.05). Forty-eight CMS patients concurrent with syringomyelia were associated with higher Cobb angle of main curve and lower SEPs amplitude than those without syringomyelia (p < 0.05). No significant difference was found between CMS patients with and without syringomyelia in age, height, SEPs latency, MEPs amplitude or rate of abnormal SEPs (p > 0.05).

CONCLUSION

Neurologically asymptomatic CMS patients showed similar absolute values of neurophysiological monitoring with IS patients. The syringomyelia in CMS indicated more severe curvature and lower SEPs amplitude even after posterior fossa decompression.

Characterization of spinal cord diffusion tensor imaging metrics in clinically asymptomatic pediatric subjects with incidental congenital lesions

Study design

Retrospective study.

Objectives

To perform quantitative DTI measurements of the entire cervical and thoracic spinal cord (SC) in typically developing (TD) pediatric subjects with incidental findings of syringomyelia or hydromyelia on conventional MRI and in a TD population without any abnormalities.

Setting

USA.

Methods

26 TD recruited as part of large SC DTI study, four of these had incidental findings. Axial DTI images were acquired on 3T MR scanner to cover the cervical and thoracic SC. We performed group analysis of DTI values in the cord above and below the MR-defined lesion. For single-subject analysis, the cord above and below the lesion was compared to average values of TD population. A standard least squares regression model was used to compare DTI parameters fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) between TD population and subjects with hydromyelia and syringomyelia. A p value of 0.05 was used for statistical significance.

Results

In group analysis, MD and AD were significantly different in cord above the lesion in subjects with hydromyelia and syringomyelia (n = 4) compared to TD population (n = 22). For single-subject analysis, DTI parameters were significantly different in cord above the syringomyelia and below the syringomyelia; MD, AD, and RD were significantly different. A subject with hydromyelia showed significant difference in FA below the lesion.

Conclusions

This study demonstrates that DTI has the potential to be used as an imaging biomarker to evaluate SC above and below the congenital lesion in syringohydromyelia subjects.

Syringohydromyelia in Patients with Chiari I Malformation: A Retrospective Analysis

BACKGROUND AND PURPOSE

The association of syringohydromyelia with Chiari I malformation has a wide range, between 23% and 80% of cases in the current literature. In our experience, this range might be overestimated compared with our observations in clinical practice. Because there is an impact of Chiari I malformation-associated syringohydromyelia on morbidity and surgical intervention, its diagnosis is critical in this patient population. Identifying related variables on the basis of imaging would also help identify those patients at risk of syrinx formation during their course of disease.

MATERIALS AND METHODS

We performed a retrospective analysis of the MR imaging studies of 108 consecutive cases of Chiari I malformation. A multitude of factors associated with syrinx formation were investigated, including demographic, morphometric, osseous, and dynamic CSF flow evaluation.

RESULTS

Thirty-nine of 108 (36.1%) patients with Chiari I malformation had syringohydromyelia. On the basis of receiver operating characteristic curve analysis, a skull base angle (nasion-sella-basion) of 135° was found to be a statistically significant classifier of patients with Chiari I malformation with or without syringohydromyelia. Craniocervical junction osseous anomalies (OR = 4.3, P = .001) and a skull base angle of >135° (OR = 4.8, P = .0006) were most predictive of syrinx formation. Pediatric patients (younger than 18 years of age) who developed syringohydromyelia were more likely to have associated skull base osseous anomalies than older individuals (P = .01).

CONCLUSIONS

Our findings support evidence of the role of foramen magnum blockage from osseous factors in the development of syringohydromyelia in patients with Chiari I malformation.

Translating state-of-the-art spinal cord MRI techniques to clinical use: A systematic review of clinical studies utilizing DTI, MT, MWF, MRS, and fMRI

BACKGROUND

A recent meeting of international imaging experts sponsored by the International Spinal Research Trust (ISRT) and the Wings for Life Foundation identified 5 state-of-the-art MRI techniques with potential to transform the field of spinal cord imaging by elucidating elements of the microstructure and function: diffusion tensor imaging (DTI), magnetization transfer (MT), myelin water fraction (MWF), MR spectroscopy (MRS), and functional MRI (fMRI). However, the progress toward clinical translation of these techniques has not been established.

METHODS

A systematic review of the English literature was conducted using MEDLINE, MEDLINE-in-Progress, Embase, and Cochrane databases to identify all human studies that investigated utility, in terms of diagnosis, correlation with disability, and prediction of outcomes, of these promising techniques in pathologies affecting the spinal cord. Data regarding study design, subject characteristics, MRI methods, clinical measures of impairment, and analysis techniques were extracted and tabulated to identify trends and commonalities. The studies were assessed for risk of bias, and the overall quality of evidence was assessed for each specific finding using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework.

RESULTS

A total of 6597 unique citations were identified in the database search, and after full-text review of 274 articles, a total of 104 relevant studies were identified for final inclusion (97% from the initial database search). Among these, 69 studies utilized DTI and 25 used MT, with both techniques showing an increased number of publications in recent years. The review also identified 1 MWF study, 11 MRS studies, and 8 fMRI studies. Most of the studies were exploratory in nature, lacking a priori hypotheses and showing a high (72%) or moderately high (20%) risk of bias, due to issues with study design, acquisition techniques, and analysis methods. The acquisitions for each technique varied widely across studies, rendering direct comparisons of metrics invalid. The DTI metric fractional anisotropy (FA) had the strongest evidence of utility, with moderate quality evidence for its use as a biomarker showing correlation with disability in several clinical pathologies, and a low level of evidence that it identifies tissue injury (in terms of group differences) compared with healthy controls. However, insufficient evidence exists to determine its utility as a sensitive and specific diagnostic test or as a tool to predict clinical outcomes. Very low quality evidence suggests that other metrics also show group differences compared with controls, including DTI metrics mean diffusivity (MD) and radial diffusivity (RD), the diffusional kurtosis imaging (DKI) metric mean kurtosis (MK), MT metrics MT ratio (MTR) and MT cerebrospinal fluid ratio (MTCSF), and the MRS metric of N-acetylaspartate (NAA) concentration, although these results were somewhat inconsistent.

CONCLUSIONS

State-of-the-art spinal cord MRI techniques are emerging with great potential to improve the diagnosis and management of various spinal pathologies, but the current body of evidence has only showed limited clinical utility to date. Among these imaging tools DTI is the most mature, but further work is necessary to standardize and validate its use before it will be adopted in the clinical realm. Large, well-designed studies with a priori hypotheses, standardized acquisition methods, detailed clinical data collection, and robust automated analysis techniques are needed to fully demonstrate the potential of these rapidly evolving techniques.