Diagnostic accuracy of diffusion tensor imaging for pediatric cervical spinal cord injury

STUDY DESIGN

Cross-sectional non-experimental study.

OBJECTIVES

To examine diagnostic accuracy of diffusion tensor imaging (DTI) for pediatric spinal cord injury (SCI).

SETTING

Pediatric Orthopedic Hospital.

METHODS

Thirty-five subjects, 10 SCI and 25 controls, mean age 13.38 years underwent two scans with 3.0 T MR scanner. Fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD) values were calculated. Subjects with SCI underwent examination of muscle strength, sensation and sacral sparing. Mean and s.d. values for FA, AD and RD were compared by group (controls, SCI with sacral sparing, SCI without sacral sparing) using analysis of variance for repeated measures. Comparisons were also made of DTI values at the injury site to values from cervical regions outside of the injury site. Specificity, sensitivity, receiver operating characteristics area under the curve (ROC AUC) and corresponding 95% confidence intervals were calculated. Resampling methods were used to validate the estimates from the final models.

RESULTS

FA values differed among SCI subjects with intact sacral sparing, absent sacral sparing and controls, P<0.003 (adjusted). DTI values in combination showed the strongest diagnostic accuracy for predicting the presence of anal contraction (AD, RD; ROC AUC=0.90), deep anal pressure (FA; ROC AUC=0.88), S4-5 sensation (FA, RD; ROC AUC=0.93), motor level (FA, AD, RD; ROC AUC=0.92) and MRI level (FA, AD, RD; ROC AUC=0.92). Bootstrap and Jackknife median values indicated consistency of the parameter estimates.

CONCLUSION

The predictive accuracy of DTI for sacral sparing end points and motor and MRI level of injury was good to strong.

[Sagittal balance and compensatory mechanism after segmental instrumentation for adolescent idiopathic scoliosis]

PURPOSE

Previous studies have demonstrated good ability to improve the sagittal profile with the use of segmental instrumentation for adolescent idiopathic scoliosis (AIS) by analysing the sagittal vertical axis (SVA). However, several authors recommend analysing the spinopelvic relation in addition to the SVA. While compensatory mechanisms may neutralise a positive SVA, these mechanisms are energy consuming and may lead to unphysiological biomechanics, which can negatively influence the quality of life. The purpose of this radiographic analysis was to analyse global sagittal balance and to identify potential compensatory mechanisms after segmental instrumentation for AIS.

METHODS

From a prospectively collected multicentre database, patients with segmental instrumentation for AIS and a minimum follow-up of 2 years were identified. An additional inclusion criterion was the ability to measure lumbar lordosis (LL), pelvic tilt (PT), pelvic incidence (PI), and SVA on each X-ray (preoperative, 1st erect, and the 2-year follow-up visits). LL was analysed in relation to PI in order to identify iatrogenic changes. Changes in LL were correlated to changes in PT and SVA.

RESULTS

91 patients were included. On the 1st erect X-ray, LL significantly decreased from pre-op but the SVA remained stable due to a significant increase of PT. At two years follow-up, PT recurred to preoperative values, accompanied by a significant increase of SVA despite a compensatory hyperlordosis below the instrumentation. The temporary increase of PT on the 1st erect was significantly correlated to an iatrogenic decrease of LL. An iatrogenic decrease of LL was significantly correlated to an increase of SVA on the 1st erect and at 2 years follow-up.

CONCLUSION

An iatrogenic decrease of LL after segmental instrumentation for AIS is initially compensated for by pelvic retroversion and later by a hyperlordosis below the instrumentation.

Diffusion tensor imaging of the normal pediatric spinal cord using an inner field of view echo-planar imaging sequence

BACKGROUND AND PURPOSE

DTI in the brain has been well established, but its application in the spinal cord, especially in pediatrics, poses several challenges. The small cord size has inherent low SNR of the diffusion signal intensity, respiratory and cardiac movements induce artifacts, and EPI sequences used for obtaining diffusion indices cause eddy-current distortions. The purpose of this study was to 1) evaluate the accuracy of cervical spinal cord DTI in children using a newly developed iFOV sequence with spatially selective 2D-RF excitations, and 2) examine reproducibility of the DTI measures.

MATERIALS AND METHODS

Twenty-five typically developing subjects were imaged twice using a 3T scanner. Axial DTI images of the cervical spinal cord were acquired with this sequence. After motion correction, DTI indices were calculated using regions of interest manually drawn at every axial section location along the cervical spinal cord for both acquisitions. Various DTI indices were calculated: FA, AD, RD, MD, RA, and VR. Geometric diffusion measures were also calculated: Cp, Cl, and Cs.

RESULTS

The following average values for each index were obtained: FA = 0.50 ± 0.11; AD = 0.97 ± 0.20 × 10(-3)mm(2)/s; RD = 0.41 ± 0.13 × 10(-3)mm(2)/s; MD = 0.59 ± 0.15 × 10(-3)mm(2)/s; RA = 0.35 ± 0.08; VR = 0.03 ± 0.00; Cp = 0.13 ± 0.07; Cl = 0.29 ± 0.09; and Cs = 0.58 ± 0.11. The reproducibility tests showed moderate to strong ICC in all subjects for all DTI parameters (ICC>0.72).

CONCLUSIONS

This study showed that accurate and reproducible DTI parameters can be estimated in the pediatric cervical spinal cord using an iFOV EPI sequence.

Diffusion tensor imaging of the pediatric spinal cord at 1.5T: preliminary results

BACKGROUND AND PURPOSE

Recent studies suggest that pediatric subjects as old as 8-years-of-age may have difficulty with the ISNCSCI examinations. Our aim was to investigate DTI parameters of healthy spinal cord in children with noncervical IS for comparison with children with SCI and to prospectively evaluate reliability measures of DTI and to correlate the measures obtained in children with SCI with the ISNCSCI.

MATERIALS AND METHODS

Five controls with thoracic and lumbar IS and 5 children with cervical SCI were imaged twice by using a single-shot echo-planar diffusion-weighted sequence. Axial imaging was performed to cover the entire cervical spinal cord in controls. For the SCI subjects, 2 vertebral bodies above and below the injury were imaged. FA and D values were obtained at different levels of the cervical spinal cord. All subjects with SCI had undergone ISNCSCI clinical examinations. Statistical analysis was performed to access differences of the DTI indices between the controls and SCI subjects, reproducibility measurements, and correlations between DTI and ISNCSCI.

RESULTS

Subjects with SCI showed reduced FA and increased D values compared with controls. Test-retest reproducibility showed good ICC coefficients in all the DTI index values among controls (≥0.9), while the SCI group showed moderate ICC (≥0.77). There were statistically significant correlations between the various DTI indices and ISNCSCI scores.

CONCLUSIONS

Preliminary DTI indices in children were determined and showed good reproducibility. Reduced FA and increased D values were seen in children with SCI in comparison with controls and showed good clinical correlation with ISNCSCI examinations.

Intra-operative magnetic resonance imaging in neurosurgery

Intra-operative MRI (iMRI) has been incorporated into modern neurosurgical operating rooms as a guide for neurosurgical interventions for almost ten years. This technology has been shown to be a useful modality in brain tumour surgery and biopsy; its use in spine, vascular and epilepsy surgery has been evolving. It is particularly useful in low-grade gliomas, pituitary adenomas and pediatric tumors. We evaluate currently available iMRI systems and their applications in neurosurgery. Future possibilities related to iMRI systems are mentioned in the light of current advances.

Spinal angiolipoma: case report and review of the literature

Spinal angiolipomas are rare lesions usually found in the epidural space of the thoracic spine. This report presents a case of and reviews the literature on this rare entity. The etiology, clinical presentation, imaging, and treatment are discussed. In 92 reported cases of spinal angiolipoma 56 occurred in women (61%), and 36 in men (39%). Mean age of occurrence is 42.9 years (range 10 days-85 years) with most patients presenting with slowly progressive symptoms of spinal cord compression. Most cases occur in the extradural compartment, and are of the non-invasive subtype. This rare clinical entity must be considered in the differential diagnosis of spinal epidural lesions. In most cases complete removal is possible, however, prognosis is good even for infiltrating lesions. Thus, one must not risk neurological damage to attain complete resection.

Differential susceptibility to neurotoxicity mediated by neurotrophins and neuronal nitric oxide synthase

NMDA neurotoxicity, which is mediated, in part, by formation of nitric oxide (NO) via activation of neuronal NO synthase (nNOS), is modulated by neurotrophins. nNOS expression in rat and mouse primary neuronal cultures grown on a glial feeder layer is significantly less than that of neurons grown on a polyornithine (Poly-O) matrix. Neurotrophins markedly increase the number of nNOS neurons, nNOS protein, and NOS catalytic activity and enhance NMDA neurotoxicity via NO-dependent mechanisms when neurons are grown on glial feeder layers. In contrast, when rat or mouse primary cortical neurons are grown on a Poly-O matrix, neurotrophins have no influence on nNOS neuronal number or NOS catalytic activity and reduce NMDA neurotoxicity. Primary neuronal cultures from mice lacking nNOS grown on a glial feeder layer fail to respond to neurotrophin-mediated enhancement of neurotoxicity. Together, these results indicate that nNOS expression and NMDA NO-mediated neurotoxicity are dependent, in part, on the culture paradigm, and neurotrophins regulate the susceptibility to NMDA neurotoxicity via modulation of nNOS. Furthermore, these results support the idea that NMDA neurotoxicity in culture is critically dependent on the developmental state of the neurons being assessed and suggest that, when cortical neurons are cultured on a glial feeder layer, they do not reach nearly as mature a phenotype as when grown on a Poly-O matrix.

Nitric oxide synthase in models of focal ischemia

BACKGROUND AND PURPOSE

Cessation of blood flow to the brain, for even a few minutes, sets in motion a potential reversible cascade of events resulting in neuronal cell death. Oxygen free radicals and oxidants appear to play an important role in central nervous system injury after cerebral ischemia and reperfusion. Recently, divergent roles for the newly identified neuronal messenger molecule and oxygen radical, nitric oxide (NO), have been identified in various models of cerebral ischemia. Because of the chemical and physical properties of NO, the numerous physiological activities it mediates, and the lack of specific agents to modulate the activity of the different isoforms of NO synthase (NOS), reports regarding the role of NO in focal cerebral ischemia have been confounding and often conflicting. Recent advances in pharmacology and the development of transgenic knockout mice specific for the different isoforms of NOS have advanced our knowledge and clarified the role of NO in cerebral ischemia.

METHODS

Animal models of focal ischemia employ occlusion of nutrient cerebral vessels, most commonly the middle cerebral artery. Primary cortical cultures are exposed to excitotoxic or ischemic conditions, and the activities of NOS isoforms or NO production are evaluated. Transgenic mice lacking expression of either the neuronal isoform of NOS (nNOS), the endothelial isoform of NOS (eNOS), or the immunologic isoform of NOS (iNOS) have been examined in models of excitotoxic injury and ischemia.

RESULTS

Excitotoxic or ischemic conditions excessively activate nNOS, resulting in concentrations of NO that are toxic to surrounding neurons. Conversely, NO generated from eNOS is critical in maintaining cerebral blood flow and reducing infarct volume. iNOS, which is not normally present in healthy tissue, is induced shortly after ischemia and contributes to secondary late-phase damage.

CONCLUSIONS

Pharmacological and genetic approaches have significantly advanced our knowledge regarding the role of NO and the different NOS isoforms in focal cerebral ischemia. nNOS and iNOS play key roles in neurodegeneration, while eNOS plays a prominent role in maintaining cerebral blood flow and preventing neuronal injury.