Diffusion tensor imaging of white and grey matter within the spinal cord of normal Beagle dogs: Sub-regional differences of the various diffusion parameters

Case report: Magnetic resonance imaging features with postoperative improvement of atypical cervical glioma characterized by predominant extramedullary distribution in a dog

Introduction

Intramedullary cord tumors present diagnostic and therapeutic challenges. Furthermore, spinal cord tumors can move across compartments, making antemortem diagnosis difficult, even with advanced imaging. This report presents a rare case of a cranial cervical spinal glioma, confirmed by surgical histopathology, with postoperative improvement in a dog.

Case description

A 9-year-old female Maltese dog presented with kyphotic posture, progressive left hemiparesis, and decreased appetite. Neurological examination revealed neck pain and decreased proprioception in the left limbs along with intact deep pain perception. Two days later, the patient developed non-ambulatory tetraparesis. Magnetic resonance imaging (MRI) revealed an ovoid, well-defined mass with homogeneously marked contrast enhancement in the second cervical spinal cord that severely compressed the spinal cord. This mass was heterogeneously hyperintense on T2-weighted images and iso-to-hypointense on T1-weighted images, showing an appearance resembling the "golf-tee" and "dural tail" signs. The MRI findings suggested an intradural extramedullary tumor. Intraoperatively, a well-demarcated mass which was locally adherent to the spinal meninges was removed. Both histopathological and genomic tumor tests were indicative of a glioma. Approximately 2 weeks postoperatively, the patient's neurological signs returned to normal.

Conclusion

This case report describes an atypical cervical glioma with complicated MR characteristics in a dog, where MRI helped guide surgical intervention.

Porcine Model of the Growing Spinal Cord-Changes in Diffusion Tensor Imaging Parameters

Diffusion tensor imaging (DTI) is an advanced magnetic resonance imaging (MRI) technique that has promising applications for the objective assessment of the microstructure of the spinal cord. This study aimed to verify the parameters obtained using DTI change during the growth process. We also wanted to identify if the DTI values change on the course of the spinal cord. The model organism was a healthy growing porcine spinal cord (19 pigs, Polish White, weight 24-120 kg, mean 48 kg, median 48 kg, age 2.5-11 months, mean 5 months, median 5.5 months). DTI parameters were measured in three weight groups: up to 29 kg (five pigs), 30-59 kg (six pigs), and from 60 kg up (eight pigs). DTI was performed with a 1.5 Tesla magnetic resonance scanner (Philips, Ingenia). Image post-processing was done using the Fiber Track package (Philips Ingenia workstation) by manually drawing the regions of interest (nine ROIs). The measurements were recorded for three sections: the cervical, thoracolumbar and lumbar segments of the spinal cord at the C4/C5, Th13/L1, and L4/L5 vertebrae levels. In each case, one segment was measured cranially and one caudally from the above-mentioned places. The values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were obtained for each ROIs and compared. It is shown that there is a correlation between age, weight gain, and change in FA and ADC parameters. Moreover, it is noted that, with increasing weight and age, the FA parameter increases and ADC decreases, whereas the FA and ADC measurement values did not significantly change between the three sections of the spinal cord. These findings could be useful in determining the reference values for the undamaged spinal cords of animals and growing humans.

Variation in Diffusion Tensor Imaging Parameters in the Cervical and Thoracic Spinal Cord (C1-C5 and C6-T2) Segments of Normal Beagle Dogs

This study aimed to determine the characteristics and reference values of each vertebra in the cervicothoracic region by performing diffusion tensor imaging (DTI) scans and analyzing DTI parameters in normal Beagle dogs. In five adult Beagles under anesthetic maintenance, DTI was performed using a 1.5-T magnetic resonance imaging (MRI) scanner. Axial DTI was performed using three overlapping slabs to cover the cervical and thoracic spinal cords. After post-processing, DTI parameters were calculated along the entire spinal cord. Among DTI parameters, fractional anisotropy, relative anisotropy, and axonal diffusivity significantly decreased in the caudal direction. However, the apparent diffusion coefficient, radial diffusivity, and mean diffusivity values were not significantly correlated with vertebral levels. We provide evidence for the existence of segment-dependent DTI parameters in the canine cervical spinal cord. Therefore, comparisons of DTI parameters between lesions at different vertebral levels should be avoided unless normative data are available. Furthermore, the DTI data obtained in this study may contribute to the development of a clinical reference for spinal cord evaluation in dogs using DTI parameters.

MRI diffusion tensor imaging scalar values in dogs with intervertebral disc herniation: A comparison between manual and semiautomated region of interest methods

Magnetic resonance imaging (MRI) diffusion tensor imaging (DTI) measures have been described as methods for quantifying spinal cord injury and predicting outcome in dogs with intervertebral disc herniation (IVDH); however, studies comparing methods for selecting regions of interest (ROIs) are currently lacking. The aims of this retrospective, methods comparison, observational study were to compare DTI measurements acquired using manual (mROI) versus semiautomated ROI (sROI) methods and to compare DTI measurements with patient outcomes. Magnetic resonance imaging scans that included DTI pulse sequences were retrieved for 65 dogs with confirmed IVDH. Regions of interest were placed at one vertebral length cranial and caudal to the region of spinal cord compression (RSCC) using the mROI and sROI methods. Scalar values based on the mROI and sROI methods were compared. There was a significant difference for all DTI measures (P < 0.0001), where fractional anisotropy was higher (95% confidence interval [CI]: 0.15, 0.19) and mean diffusivity (MD; CI: -0.41, -0.35), axial diffusivity (AD; CI: -0.47, -0.36) and radial diffusivity (RD; CI: -0.36, -0.27) were lower for the mROI than for the sROI. For both the mROI and sROI, MD, AD, and RD were significantly lower (p < 0.05) at the RSCC in paraplegic dogs that did not regain motor function. The findings indicated that DTI methods for quantifying SCI using open source software and ROI were feasible for use in dogs with IVDH; however, values based on sROI methods differed from values based on mROI methods. Some DTI measures based on both the mROI and sROI methods were predictive of poor patient outcome.

In vivo detection of microstructural spinal cord lesions in dogs with degenerative myelopathy using diffusion tensor imaging

Background

Degenerative myelopathy (DM) in dogs is a progressive neurodegenerative condition that causes white matter spinal cord lesions. These lesions are undetectable on standard magnetic resonance imaging (MRI), limiting diagnosis and monitoring of the disease. Spinal cord lesions cause disruption to the structural integrity of the axons causing water diffusion to become more random and less anisotropic. These changes are detectable by the technique of diffusion tensor imaging (DTI) which is highly sensitive to diffusion alterations secondary to white matter lesion development.

Objective

Perform spinal DTI on cohorts of dogs with and without DM to identify if lesions caused by DM will cause a detectable alteration in spinal cord diffusivity that correlates with neurological status.

Animals

Thirteen dogs with DM and 13 aged‐matched controls.

Methods

All animals underwent MRI with DTI of the entire spine. Diffusivity parameters fractional anisotropy (FA) and mean diffusivity (MD) were measured at each vertebral level and statistically compared between groups.

Results

Dogs with DM had significant decreases in FA within the regions of the spinal cord that had high expected lesion load. Decreases in FA were most significant in dogs with severe forms of the disease and correlated with neurological grade.

Conclusions and Clinical Importance

Findings suggest that FA has the potential to be a biomarker for spinal cord lesion development in DM and could play an important role in improving diagnosis and monitoring of this condition.

Diagnostic Imaging in Intervertebral Disc Disease

Imaging is integral in the diagnosis of canine intervertebral disc disease (IVDD) and in differentiating subtypes of intervertebral disc herniation (IVDH). These include intervertebral disc extrusion (IVDE), intervertebral disc protrusion (IVDP) and more recently recognized forms such as acute non-compressive nucleus pulposus extrusion (ANNPE), hydrated nucleus pulposus extrusion (HNPE), and intradural/intramedullary intervertebral disc extrusion (IIVDE). Many imaging techniques have been described in dogs with roles for survey radiographs, myelography, computed tomography (CT), and magnetic resonance imaging (MRI). Given how common IVDH is in dogs, a thorough understanding of the indications and limitations for each imaging modality to aid in diagnosis, treatment planning and prognosis is essential to successful case management. While radiographs can provide useful information, especially for identifying intervertebral disc degeneration or calcification, there are notable limitations. Myelography addresses some of the constraints of survey radiographs but has largely been supplanted by cross-sectional imaging. Computed tomography with or without myelography and MRI is currently utilized most widely and have become the focus of most contemporary studies on this subject. Novel advanced imaging applications are being explored in dogs but are not yet routinely performed in clinical patients. The following review will provide a comprehensive overview on common imaging modalities reported to aid in the diagnosis of IVDH including IVDE, IVDP, ANNPE, HNPE, and IIVDE. The review focuses primarily on canine IVDH due to its frequency and vast literature as opposed to feline IVDH.

The role of diffusion tensor imaging as an objective tool for the assessment of motor function recovery after paraplegia in a naturally-occurring large animal model of spinal cord injury

Background

Traumatic spinal cord injury (SCI) results in sensory and motor function impairment and may cause a substantial social and economic burden. For the implementation of novel treatment strategies, parallel development of objective tools evaluating spinal cord (SC) integrity during motor function recovery (MFR) is needed. Diffusion tensor imaging (DTI) enables in vivo microstructural assessment of SCI.

Methods

In the current study, temporal evolvement of DTI metrics during MFR were examined; therefore, values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured in a population of 17 paraplegic dogs with naturally-occurring acute SCI showing MFR within 4 weeks after surgical decompression and compared to 6 control dogs. MRI scans were performed preoperatively and 12 weeks after MFR was observed. DTI metrics were obtained at the lesion epicentre and one SC segment cranially and caudally. Variance analyses were performed to compare values between evaluated localizations in affected dogs and controls and between time points. Correlations between DTI metrics and clinical scores at follow-up examinations were assessed.

Results

Before surgery, FA values at epicentres were higher than caudally (p = 0.0014) and control values (p = 0.0097); ADC values were lower in the epicentre compared to control values (p = 0.0035) and perilesional (p = 0.0448 cranially and p = 0.0433 caudally). In follow-up examinations, no significant differences could be found between DTI values from dogs showing MFR and control dogs. Lower ADC values at epicentres correlated with neurological deficits at follow-up examinations (r = − 0.705; p = 0.0023).

Conclusions

Findings suggest that a tendency to the return of DTI values to the physiological situation after surgical decompression accompanies MFR after SCI in paraplegic dogs. DTI may represent a useful and objective clinical tool for follow-up studies examining in vivo SC recovery in treatment studies.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1630-4) contains supplementary material, which is available to authorized users.

The Relationship between Lesion Severity Characterized by Diffusion Tensor Imaging and Motor Function in Chronic Canine Spinal Cord Injury

Lesion heterogeneity among chronically paralyzed dogs after acute, complete thoracolumbar spinal cord injury (TLSCI) is poorly described. We hypothesized that lesion severity quantified by diffusion tensor imaging (DTI) is associated with hindlimb motor function. Our objectives were to quantify lesion severity with fractional anisotropy (FA), mean diffusivity (MD), and tractography and investigate associations with motor function. Twenty-two dogs with complete TLSCI in the chronic stage were enrolled and compared with six control dogs. All underwent thoracolumbar magnetic resonance imaging (MRI) with DTI and gait analysis. FA and MD were calculated on regions of interest (ROI) at the lesion epicenter and cranial and caudal to the visible lesion on conventional MRI and in corresponding ROI in controls. Tractography was performed to detect translesional fibers. Gait was quantified using an ordinal scale (OFS). FA and MD values were compared between cases and controls, and relationships between FA, MD, presence of translesional fibers and OFS were investigated. The FA at the epicenter (median: 0.228, 0.107-0.320), cranial (median: 0.420, 0.391-0.561), and caudal to the lesion (median: 0.369, 0.265-0.513) was lower than combined ROI in controls (median: 0.602, 0.342-0.826, p < 0.0001). The MD at the epicenter (median: 2.06 × 10^-3, 1.33-2.96 × 10^-3) and cranially (median: 1.52 × 10^-3, 1.03-1.87 × 10^-3) was higher than combined ROI in controls (median: 1.28 × 10^-3, 0.81-1.44 × 10^-3, p ≤ 0.001). Four dogs had no translesional fibers. Median OFS was 2 (0-6). The FA at the lesion epicenter and presence of translesional fibers were associated with OFS (p ≤ 0.0299). DTI can detect degeneration and physical transection after severe TLSCI. Findings suggest DTI quantifies injury severity and suggests motor recovery in apparently complete dogs is because of supraspinal input.

Characterization of Chronic Axonal Degeneration Using Diffusion Tensor Imaging in Canine Spinal Cord Injury: A Quantitative Analysis of Diffusion Tensor Imaging Parameters According to Histopathological Differences

Diffusion tensor imaging (DTI) is more sensitive than conventional magnetic resonance imaging (MRI) for the identification of axonal degeneration. However, no study to date has used DTI to evaluate the severity of axonal degeneration in canine spinal cord injury (SCI). Therefore, the aim of this study was to characterize multi-grade axonal degeneration (mild, moderate, and severe) in a canine model of spinal cord compression injury using DTI. MRI data were obtained from 6 normal dogs and 5 dogs with lumbar SCI 78 days after SCI (L1-L3) using a 3 Tesla MRI scanner. For DTI, transverse multi-shot echo planar imaging sequences (b-value = 0; 800 s/mm²; 12 directions) were used. Regions of interest on DTI maps were selected based on areas of normal white matter (NWM) and mild, moderate, and severe axonal degeneration (AxD) on histopathological images. Statistically significant differences were observed between NWM and AxD, and among different severities of AxD. The severity of AxD demonstrated a negative linear correlation with fractional anisotropy and positive linear correlations with spherical index and radial diffusivity; additionally, positive U-shaped correlations were identified between the severity of AxD and mean diffusivity and axial diffusity (AD). These results demonstrate a potential clinical application for DTI in the noninvasive monitoring of histological changes post-SCI. DTI could be utilized for the early diagnosis and assessment of SCI and, ultimately, used to optimize the treatment and rehabilitation of SCI patients.

Comparison of Preoperative Quantitative Magnetic Resonance Imaging and Clinical Assessment of Deep Pain Perception as Prognostic Tools for Early Recovery of Motor Function in Paraplegic Dogs with Intervertebral Disk Herniations

Background

Prognostic tools to predict early postoperative motor function recovery (MFR) after thoracolumbar intervertebral disk herniation (IVDH) in paraplegic dogs represent an opportunity to timely implement novel therapies that could shorten recovery times and diminish permanent neurological dysfunctions.

Hypothesis

Fractional anisotropy (FA) values obtained using diffusion tensor imaging have a higher prognostic value than a lesion extension ratio in T2‐weighted images (T2W‐LER) and clinical assessment of deep pain perception (DPP) for MFR.

Animals

Thirty‐five paraplegic dogs with diagnosis of acute or subacute thoracolumbar IVDH.

Methods

Prospective, descriptive observational study. At admission, absence or presence of DPP, T2W‐LER, and FA values was evaluated. MFR was assessed within 4 weeks after decompressive surgery. Values of T2W‐LER and FA of dogs with and without MFR were compared using t‐tests. All 3 methods were evaluated for their sensitivity and specificity as a prognostic factor.

Results

No differences were found between groups regarding T2W‐LER. FA values differed statistically when measured caudally of lesion epicenter being higher in dogs without MFR compared to dogs with MFR (P = .023). Logistic regression analysis revealed significance in FA values measured caudally of the lesion epicenter (P = .033, area under the curve = 0.72). Using a cutoff value of FA = 0.660, the technique had a sensitivity of 80% and a specificity of 55%. Evaluation of DPP had a sensitivity of 73.3% and specificity of 75% (P = .007).

Conclusions and Clinical Importance

Evaluation of DPP showed a similar sensitivity and a better specificity predicting early MFR than quantitative magnetic resonance imaging.