Omar Islam

Plasticity of the Injured Human Spinal Cord: Insights Revealed by Spinal Cord Functional MRI

Introduction While numerous studies have documented evidence for plasticity of the human brain there is little evidence that the human spinal cord can change after injury. Here, we employ a novel spinal fMRI design where we stimulate normal and abnormal sensory dermatomes in persons with traumatic spinal cord injury and perform a connectivity analysis to understand how spinal networks process information. Methods Spinal fMRI data was collected at 3 Tesla at two institutions from 38 individuals using the standard SEEP functional MR imaging techniques. Thermal stimulation was applied to four dermatomes in an interleaved timing pattern during each fMRI acquisition. SCI patients were stimulated in dermatomes both above (normal sensation) and below the level of their injury. Sub-group analysis was performed on healthy controls (n = 20), complete SCI (n = 3), incomplete SCI (n = 9) and SCI patients who recovered full function (n = 6). Results Patients with chronic incomplete SCI, when stimulated in a dermatome of normal sensation, showed an increased number of active voxels relative to controls (p = 0.025). There was an inverse relationship between the degree of sensory impairment and the number of active voxels in the region of the spinal cord corresponding to that dermatome of abnormal sensation (R2 = 0.93, p<0.001). Lastly, a connectivity analysis demonstrated a significantly increased number of intraspinal connections in incomplete SCI patients relative to controls suggesting altered processing of afferent sensory signals. Conclusions In this work we demonstrate the use of spinal fMRI to investigate changes in spinal processing of somatosensory information in the human spinal cord. We provide evidence for plasticity of the human spinal cord after traumatic injury based on an increase in the average number of active voxels in dermatomes of normal sensation in chronic SCI patients and an increased number of intraspinal connections in incomplete SCI patients relative to healthy controls.

Posterior fossa measurements in patients with and without Chiari I malformation.

PURPOSE To determine if there is a correlation between cerebellar tonsillar descent in patients with and without Chiari I malformation and three skull morphometric measurements: clivus length, anteroposterior diameter of the foramen magnum, and Boogards angle. METHODS Cerebellar tonsillar descent, clivus length, anteroposterior diameter of the foramen magnum, and Boogards angle were measured in mid-sagittal T1-weighted magnetic resonance images of 188 patients. The study included 81 patients with Chiari I malformations (CMI). Without identifiable pathology, 107 patients served as a comparison group. Two-sample t-tests were used to assess for significance. A Pearson correlation matrix was constructed to assess the strength of linear dependence between measured parameters for the study population. RESULTS A negative correlation was found between tonsillar herniation and clivus length (r = -0.30, P < 0.001), while a positive correlation was found between tonsillar herniation and foramen magnum size (r = 0.15, P = 0.0431), and Boogards angle (r = 0.23, P = 0.0014). Clivus length was shorter (P = 0.0009) in CMI patients (4.02 cm ± 0.45) than comparison patients (4.23 cm ± 0.42). In addition, the anteroposterior diameter of the foramen magnum was wider (P = 0.0412) (3.74 cm ± 0.40 compared to 3.63 ± 0.30) and Boogards angle was larger (P = 0.0079) (123.58 degrees ± 8.27 compared to 120.62 degrees ± 6.79) with CMI. CONCLUSION A greater degree of cerebellar tonsillar herniation is associated with a shorter clivus length, a wider anteroposterior diameter of foramen magnum, and a wider Boogards angle.

Hereditary diffuse leukoencephalopathy with neuroaxonal spheroids: novel imaging findings

Hereditary diffuse leukoencephalopathy with neuroaxonal spheroids (HDLS) is a paediatric autosomal dominant dysmyelinating disease.1 Rare adult onset cases manifest with personality change, cognitive decline and gait impairment.1–3 Diagnosis is often made following brain biopsy with the presence of giant neuroaxonal swellings known as spheroids.4 Characteristic brain MRI abnormalities of HDLS include decreased T1-weighted signal intensity of the frontoparietal white matter and corpus callosum.2 T2-weighted images reveal patchy increased signal intensity in the subcortical white matter with corticospinal tract involvement.1–4 To our knowledge, this is the first report of an abnormal apparent diffusion coefficient (ADC) map in HDLS. A previously healthy 46-year-old man presented following a 1 year history of slurred speech and word finding difficulty that progressed until …

Diffusion MRI Brain Findings in Neonates Exposed to Chorioamnionitis: A Case Series

OBJECTIVE The primary objective of this study was to determine the feasibility of using diffusion-weighted magnetic resonance imaging (DWMRI) to assess white matter changes in high-risk neonates. Secondary objectives were to determine if exposure to chorioamnionitis (clinical or histopathologic) is associated with DWMRI findings in the neonatal brain, and to calculate the sample size required for a more definitive prospective cohort study. METHODS Seventeen women with PPROM (preterm premature rupture of the membranes) who delivered 18 infants not requiring ventilatory support were recruited to participate in this case series. When stable, infants underwent DWMRI scanning. All placentas were examined for evidence of histopathologic chorioamnionitis (HCA). RESULTS There was histopathologic evidence of chorioamnionitis in seven of the 18 placentas examined; three of these patients had clinical chorioamnionitis. Diffusion MRI revealed changes in both the diffusion-weighted imaging and the apparent diffusion coefficient in three of the seven infants confirmed to have HCA (43%), while only one of the 11 infants with normal placentas (9%) showed similar findings. Routine head ultrasound examination demonstrated abnormal cortical findings that would normally prompt further investigation in only one of these infants. CONCLUSION Exposure to HCA may be associated with abnormal DWMRI findings on imaging of the neonatal brain within 96 hours of delivery. Further study is required to delineate the association of chorioamnionitis and white matter changes with long-term neurodevelopmental sequelae.

Cognitive Function and 3-Tesla Magnetic Resonance Imaging Tractography of White Matter Hyperintensities in Elderly Persons

Background/Aims: This study used 3-Tesla magnetic resonance imaging (MRI) tractography to determine if there was an association between tracts crossing white matter hyperintensities (WMH) and cognitive function in elderly persons. Methods: Brain T2-weighted fluid-attenuated inversion recovery (FLAIR) and diffusion tensor MRI scans were acquired in participants above the age of 60 years. Twenty-six persons had WMH identified on T2 FLAIR scans. They completed a battery of neuropsychological tests and were classified as normal controls (n = 15) or with Alzheimers dementia (n = 11). Tractography was generated by the Fiber Assignment by Continuous Tracking method. All tracts that crossed WMH were segmented. The average fractional anisotropy and average mean diffusivity of these tracts were quantified. We studied the association between cognitive test scores with the average mean diffusivity and average fractional anisotropy of tracts while controlling for age, total WMH volume and diagnosis. Results: An increased mean diffusivity of tracts crossing WMH was associated with worse performance on the Wechsler Memory Scale-III Longest Span Forward (p = 0.02). There was no association between the fractional anisotropy of tracts and performance on cognitive testing. Conclusion: The mean diffusivity of tracts crossing WMH measured by tractography is a novel correlate of performance on the Wechsler Memory Scale-III Longest Span Forward in elderly persons.

Altered Superficial White Matter on Tractography MRI in Alzheimer's Disease.

Background/Aims: Superficial white matter provides extensive cortico-cortical connections. This tractography study aimed to assess the diffusion characteristics of superficial white matter tracts in Alzheimers disease. Methods: Diffusion tensor 3T magnetic resonance imaging scans were acquired in 24 controls and 16 participants with Alzheimers disease. Neuropsychological test scores were available in some participants. Tractography was performed by the Fiber Assignment by Continuous Tracking (FACT) method. The superficial white matter was manually segmented and divided into frontal, parietal, temporal and occipital lobes. The mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AxD) and fractional anisotropy (FA) of these tracts were compared between controls and participants with Alzheimers disease and correlated with available cognitive tests while adjusting for age and white matter hyperintensity volume. Results: Alzheimers disease was associated with increased MD (p = 0.0011), increased RD (p = 0.0019) and increased AxD (p = 0.0017) in temporal superficial white matter. In controls, superficial white matter was associated with the performance on the Montreal Cognitive Assessment, Stroop and Trail Making Test B tests, whereas in Alzheimers disease patients, it was not associated with the performance on cognitive tests. Conclusion: Temporal lobe superficial white matter appears to be disrupted in Alzheimers disease.

Tractography at 3T MRI of Corpus Callosum Tracts Crossing White Matter Hyperintensities

BACKGROUND AND PURPOSE: The impact of white matter hyperintensities on the diffusion characteristics of crossing tracts is unclear. This study used quantitative tractography at 3T MR imaging to compare, in the same individuals, the diffusion characteristics of corpus callosum tracts that crossed white matter hyperintensities with the diffusion characteristics of corpus callosum tracts that did not pass through white matter hyperintensities. MATERIALS AND METHODS: Brain T2 fluid-attenuated inversion recovery–weighted and diffusion tensor 3T MR imaging scans were acquired in 24 individuals with white matter hyperintensities. Tractography data were generated by the Fiber Assignment by Continuous Tracking method. White matter hyperintensities and corpus callosum tracts were manually segmented. In the corpus callosum, the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts crossing white matter hyperintensities were compared with the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts that did not cross white matter hyperintensities. The cingulum, long association fibers, corticospinal/bulbar tracts, and thalamic projection fibers were included for comparison. RESULTS: Within the corpus callosum, tracts that crossed white matter hyperintensities had decreased fractional anisotropy compared with tracts that did not pass through white matter hyperintensities (P = .002). Within the cingulum, tracts that crossed white matter hyperintensities had increased radial diffusivity compared with tracts that did not pass through white matter hyperintensities (P = .001). CONCLUSIONS: In the corpus callosum and cingulum, tracts had worse diffusion characteristics when they crossed white matter hyperintensities. These results support a role for white matter hyperintensities in the disruption of crossing tracts.

Anatomic Distribution of Gadolinium Contrast Medium by High-Resolution Magnetic Resonance Imaging After Peribulbar and Retrobulbar Injections

OBJECTIVE To examine the anatomic distribution of gadolinium contrast medium by high-resolution surface-coil magnetic resonance imaging after peribulbar and retrobulbar injection. METHODS Comparative case series in which 4 healthy volunteers were randomized to peribulbar (n = 2) or retrobulbar (n = 2) injection of gadolinium and lidocaine hydrochloride, 2%, without epinephrine. Magnetic resonance imaging was performed before injection and at 5 minutes and 90 minutes after injection. RESULTS The peribulbar injection technique resulted in contrast medium primarily in the extraconal space, with no gadolinium observed at the orbital apex; surprisingly, a small amount of contrast medium was observed in the pterygopalatine fossa immediately after peribulbar injection. The retrobulbar injection technique resulted in gadolinium signal diffusely enhancing the intraconal space, orbital apex, optic nerve sheath, and optic canal. The signal intensity was clearly observed in the cavernous sinus surrounding the cavernous portion of the internal carotid artery. A small amount of contrast medium was detected in the pterygopalatine fossa. CONCLUSIONS The retrobulbar injection technique localizes to the intraconal space, with access to intracranial and central nervous system structures via the optic canal, superior orbital fissure, and cavernous sinus. In contrast, the peribulbar injection technique produces a mostly extraconal distribution; however, intraconal solution may communicate with the central nervous system via the inferior orbital fissure and pterygopalatine fossa. This novel finding suggests that peribulbar anesthesia has a readily accessible route for central nervous system toxic effects. Magnetic resonance imaging with gadolinium contrast medium administration provides an important methodological advantage over previously described techniques and is a safe, reproducible, and superior method of orbital imaging.

ASSOCIATIONS BETWEEN QUANTITATIVE TRACTOGRAPHY AT 3T MRI AND COGNITIVE FUNCTION IN ALZHEIMER’S DISEASE

was apparent as a single focal spot in all but 2 MCI and 2 AD patients who displayed two or more spots bilaterally. No enhancement was detected on pre-contrast FLAIR images. Leptomeningeal enhancement was associated with (non-lacunar) cerebral and/or cerebellar ischaemic stroke presence (p1⁄40.029), and marginally with white matter hyperintensity score (p1⁄40.083). The stroke location did not correspond to the site of BBB leakage. No associations between leptomeningeal enhancement and other markers of cerebrovascular damage were found. Conclusions: Post-contrast leptomeningeal enhancement on FLAIR images is prevalent in MCI and AD and may serve as a new marker for subtle BBB leakage. This type of BBB damage may be associated with ischaemic and/or inflammatory processes and possibly relates to cortical atrophy and cognitive decline. Future longitudinal MRI studies in larger samples and with post-mortem histology are needed to reveal its role in the onset and progression of dementia.

COGNITIVE FUNCTION AND TRACTOGRAPHY OF WHITE MATTER TRACTS CROSSING HYPERINTENSITIES IN ELDERLY PERSONS

ipsilateral hippocampus, frontal and temporal cortices (Figure 1) . Conclusions: WM connectivity in dementia patients was regionally reduced in comparison to MCI patients. Such structural connectivity declines possibly reflects a higher magnitude of microstructural WM abnormalities in dementia patients. WM tract alterations might be associated with language, attention, and working memory performance and relate to key clinical features of AD-related cognitive decline.