Hippocampal subfield involvement in patients with transient global amnesia.

BACKGROUND AND PURPOSE: Transient global amnesia (TGA) is a rare neurological disorder causing a transient disturbance of episodic long-term memory. Its etiology remains yet to be identified; the only consistently reported findings in patients with TGA are small hyperintense lesions in the hippocampus on diffusion-weighted magnetic resonance imaging (DWI). The aim of this study was to define whether these lesions are subfield specific, as suggested previously. METHODS: High-resolution multiplanar reformation T1 and DWI of the hippocampus were acquired in 25 patients after TGA with a total of 43 hippocampal lesions. Hippocampal subfields were determined using the FreeSurfer software and the location of the DWI lesions was transformed to the T1 images after data co-registration. Additionally, hippocampal subfield volumes in each patient were calculated and compared with that of 20 healthy controls. RESULTS: Hippocampal lesions were most frequently detected in the cornu ammonis area 1 (CA1) subfield (30.2%), the hippocampal tail (28.0%), and the subiculum (21.0%); however, lesions were also found in other subfields. There was no significant difference between patients and controls concerning the volumes of the hippocampal subfields. CONCLUSIONS: Contrasting previous assumptions, we found DWI hyperintense lesions not to be restricted to the CA1 subfield. The visualization of focal hippocampal lesions on diffusion imaging located to several different hippocampal subfields suggests a potential pathophysiology of TGA independent of microstructural hippocampal anatomy and subfield-specific vulnerability.

Association of iron rim lesions with brain and cervical cord volume in relapsing multiple sclerosis.

OBJECTIVES: In multiple sclerosis (MS), iron rim lesions (IRLs) are indicators of chronic low-grade inflammation and ongoing tissue destruction. The aim of this study was to assess the relationship of IRLs with clinical measures and magnetic resonance imaging (MRI) markers, in particular brain and cervical cord volume. METHODS: Clinical and MRI parameters from 102 relapsing MS patients (no relapses for at least 6 months, no contrast-enhancing lesions) were included; follow-up data obtained after 12 months was available in 49 patients. IRLs were identified on susceptibility-weighted images (SWIs). In addition to standard brain and spinal cord MRI parameters, normalised cross-sectional area (nCSA) of the upper cervical cord was calculated. RESULTS: Thirty-eight patients had at least one IRL on SWI MRI. At baseline, patients with IRLs had higher EDSS scores, higher lesion loads (brain and spinal cord), and lower cortical grey matter volumes and a lower nCSA. At follow-up, brain atrophy rates were higher in patients with IRLs. IRLs correlated spatially with T1-hypointense lesions. CONCLUSIONS: Relapsing MS patients with IRLs showed more aggressive MRI disease characteristics in both the cross-sectional and longitudinal analyses. KEY POINTS: • Multiple sclerosis patients with iron rim lesions had higher EDSS scores, higher brain and spinal cord lesion loads, lower cortical grey matter volumes, and a lower normalised cross-sectional area of the upper cervical spinal cord. • Iron rim lesions are a new lesion descriptor obtained from susceptibility-weighted MRI. Our data suggests that further exploration of this lesion characteristic in regard to a poorer prognosis in multiple sclerosis patients is warranted.

MRI topography of lesions related to internuclear ophthalmoplegia in patients with multiple sclerosis or ischemic stroke.

BACKGROUND AND PURPOSE: Internuclear ophthalmoplegia is a dysfunction of conjugate eye movements, caused by lesions affecting the medial longitudinal fasciculus (MLF). Multiple sclerosis (MS) and ischemic stroke represent the most common pathophysiologies. While magnetic resonance imaging (MRI) allows for localizing lesions affecting the MLF, comprehensive comparative studies exploring potential different spatial characteristics of lesions affecting the MLF are missing until now. METHODS: We retrospectively investigated MRI examinations of 82 patients (40 patients with MS and 42 patients with ischemic stroke). For lesion localization, the brainstem was segmented into (1) ponto-medullary junction, (2) mid pons, (3) upper pons, and (4) mesencephalon. RESULTS: Corresponding lesions affecting the MLF were observed in 29/40 (72.5%) MS and 38/42 (90.5%) stroke patients. Compared to stroke patients, MS patients had significantly more lesions in multiple locations (P < .001). Stroke patients showed more lesions at the level of the mesencephalon (P < .001), while lesions at the level of the ponto-medullary junction, mid, and upper pons did not statistically differ between the groups. CONCLUSION: Our results demonstrate that multiple lesions affecting the MLF make inflammatory-demyelination due to MS more likely, while lesion localization at the level of the mesencephalon favors ischemia.

Diffusely appearing white matter in multiple sclerosis: Insights from sodium (23Na) MRI.

BACKGROUND: In multiple sclerosis (MS), magnetic resonance imaging (MRI) frequently shows ill-defined areas with intermediate signal intensity between the normal appearing white matter (NAWM) and focal T2-hyperintense lesions, termed "diffusely appearing white matter" (DAWM). Even though several advanced MRI techniques have shown the potential to detect and quantify subtle commonly not visible microscopic tissue changes, to date only a few advanced MRI studies investigated DAWM changes in a quantitative manner. The aim of this study was to detect and quantify tissue abnormalities in the DAWM in comparison to focal lesions and the NAWM in MS patients by sodium (23Na) MRI. METHODS: 23Na and conventional MRI were performed in 25 MS patients with DAWM (DAWM+) and in 25 sex- and age matched MS patients without DAWM (DAWM-), as well as in ten healthy controls (HC). Mean total sodium concentrations (TSC) were quantified in the DAWM, NAWM, normal appearing grey matter (NAGM) and in focal MS lesions. RESULTS: In MS DAWM+and DAWM-, TSC values were increased in the NAGM (DAWM+: 44.61 ± 4.09 mM; DAWM-: 45.37 ± 3.8 mM) and in the NAWM (DAWM+: 39.85 ± 3.89 mM; DAWM-: 39.82 ± 4.25 mM) compared to normal grey and white matter in HC (GM 40.87 ± 3.25 mM, WM 35.9 ± 1.81 mM; p < 0.05 for all comparisons). Interestingly, the DAWM showed similar sodium concentrations (39.32 ± 4.59 mM) to the NAWM (39.85 ± 3.89 mM), whereas TSC values in T1 hypointense (46.53 ± 7.87 mM) and T1 isointense (41.99 ± 6.10 mM) lesions were significantly higher than in the DAWM (p < 0.001 and 0.017 respectively). CONCLUSION: 23Na MRI is confirmed as a sensitive marker of even subtle tissue abnormalities. DAWM sodium levels are increased and comparable to the abnormalities in NAWM, suggesting pathological changes less severe than in focal lesions comparable to what is expected in the NAWM.

Resting-state connectivity alterations during transient global amnesia.

While the pathophysiology of transient global amnesia (TGA) is not understood, due to the specific nature of the clinical deficits, transient dysfunction in the medial temporal lobe, especially in the hippocampus, is assumed; however, concomitant disturbances in other brain regions and in executive function have been postulated. In this study, a cohort of 16 patients was prospectively recruited from the emergency department for resting-state functional MRI (fMRI) during the acute stage of TGA, as confirmed by a standardized neuropsychological assessment. Twenty age- and sex-matched controls, as well as twenty patients with a history of TGA, were recruited for comparison. Functional data were processed using independent component analysis (ICA), allowing the complete automatic (data-driven) identification of spontaneous network dynamics. We documented a severe disturbance in anterograde episodic long-term memory in all patients. Group-based ICA of resting-state data in acute TGA patients versus that of controls and patients with a past TGA episode demonstrated reduced FC mainly of structures belonging to the executive network (EN), but also the hippocampus, confirming its pathophysiological involvement in the disorder, as well as areas belonging to the salience network and other subcortical regions. No significant differences were found when comparing connectivity in patients with a history of TGA and controls. Our findings strengthen previous empirical and theoretical accounts of hippocampal and executive dysfunction in TGA. The disruption of frontal, parietal and insular control regions, together with disruption in the hippocampus, provides a new interpretation for the pathophysiology and neuropsychological profile of this neurological disorder on a large-scale network level.

Temporal evolution of acute multiple sclerosis lesions on serial sodium (23Na) MRI.

BACKGROUND: Several studies have reported the characteristics of acute multiple sclerosis (MS) lesions on diffusion-weighted magnetic resonance imaging (DWI MRI). Current publications reported a transient reduction of the apparent diffusion coefficient (ADC) delineating an early phase of lesion evolution, before increased diffusion occurs in parallel to blood-brain-barrier (BBB) breakdown. Sodium MRI might provide another perspective on lesion development, but clinical applications have been limited to high field MR systems. The objective in this study was to investigate the temporal evolution of acute MS lesions using conventional (T2-fluid-attenuated inversion recovery (T2-FLAIR) images, post-contrast T1-weighted images), diffusion and sodium MRI. METHODS: Initial and follow-up MRI (23Na and 1H MRI) were performed on a 3T scanner. Quantitative assessment of total sodium concentration (TSC) and ADC was performed. The study was designed for frequent follow-up MRI examinations during 4 weeks after the initial presentation. RESULTS: Thirty-one acute MS lesions (7 lesions with reduced diffusion) in eleven MS patients were included. On initial MRI, TSC in contrast-enhancing lesions was increased when compared to the normal-appearing white matter (NAWM), while lesions with an initial reduced diffusion showed a TSC comparable to the NAWM. On follow-up MRI, in lesions with reduced diffusion subsequent increase of ADC and TSC values occurred along with signs of the development of vasogenic edema and contrast-enhancement. After four weeks, TSC values decreased along with regression of vasogenic edema and contrast-enhancement. CONCLUSIONS: In lesions with a reduction of the ADC sodium levels are near normal and precede signs of BBB breakdown. These findings suggest a relatively preserved tissue structure in this early phase of lesion evolution.

Arterial Spin Labeling Cerebral Perfusion Magnetic Resonance Imaging in Migraine Aura: An Observational Study.

BACKGROUND: Changes in cerebral perfusion during migraine with aura (MA) have been assessed mainly using dynamic susceptibility contrast (DSC) magnetic resonance perfusion imaging. A contrast agent-free method to assess these changes would be desirable. We assessed changes in cerebral perfusion during MA using arterial spin labeling (ASL) perfusion magnetic resonance imaging. METHODS: We investigated 4 patients with a standardized protocol including ASL perfusion imaging during MA (n = 2) or early headache phase (n = 2) and asymptomatic follow-up. Semiquantitative evaluation was done using a region of interest (ROI) within hypoperfused or hyperperfused areas and corresponding ROIs in the contralateral hemisphere. Relative ratios of mean perfusion in the corresponding ROIs were calculated. DSC imaging was done at initial time points and compared visually with ASL findings. RESULTS: In all patients, regional perfusion changes were detected in the acute phase. These abnormalities did not respect the boundaries of major cerebral vascular territories but overlapped onto adjoining regions. During MA, adjacent hypoperfused and hyperperfused areas were found, whereas during headache, regional hyperperfusion only was observed. Perfusion abnormalities normalized on follow-up. CONCLUSIONS: ASL perfusion imaging is a contrast agent-free method suitable for assessment of reversible perfusion changes during or immediately after MA.

Heterogeneity of acute multiple sclerosis lesions on sodium (23Na) MRI.

BACKGROUND: Advanced magnetic resonance imaging (MRI) techniques provide a window into pathological processes in multiple sclerosis (MS). Nevertheless, to date only few studies have performed sodium MRI in MS. OBJECTIVES: We analysed total sodium concentration (TSC) in hyperacute, acute and chronic lesions in MS with (23)Na MRI. METHODS: (23)Na MRI and (1)H MRI were performed in 65 MS patients and 10 healthy controls (HC). Mean TSC was quantified in all MS lesions with a diameter of >5 mm and in the normal appearing white and grey matter (NAWM, NAGM). RESULTS: TSC in the NAWM and the NAGM of MS patients was significantly higher compared to HC (WM: 37.51 ± 2.65 mM versus 35.17 ± 3.40 mM; GM: 43.64 ± 2.75 mM versus 40.09 ± 4.64 mM). Acute and chronic MS lesions showed elevated TSC levels of different extent (contrast-enhancing lesions (49.07 ± 6.99 mM), T1 hypointense lesions (45.06 ± 6.26 mM) and remaining T1 isointense lesions (39.88 ± 5.54 mM)). However, non-enhancing hyperacute lesions with a reduced apparent diffusion coefficient showed a TSC comparable to the NAWM (37.22 ± 4.62 mM). CONCLUSIONS: TSC is not only a sensitive marker of the severity of chronic tissue abnormalities in MS but is also highly sensitive to opening of the blood-brain barrier and vasogenic tissue oedema in contrast-enhancing lesions.

Clinical and MRI patterns of pericallosal artery infarctions: the significance of supplementary motor area lesions.

Cerebral infarctions in the anterior cerebral artery (ACA) territory account for only up to 3-5% of strokes. Subject to the affected ACA branches, different clinical patterns can be defined. We report a case series of patients with isolated infarctions of the pericallosal (PC) artery territory. We analyzed 36 consecutive patients presenting over a 10-year period with isolated PC artery territory infarctions (15 left-sided, 19 right-sided, 2 bilateral) regarding clinical symptoms as well as MRI findings. Analysis of DWI lesion pattern showed complete PC artery infarctions in three patients. The majority of patients had partial infarctions predominantly involving either the superior frontal gyrus (n = 12), the corpus callosum (n = 1) or both (n = 20). Hemodynamic lesion patterns were found in 13 patients, while multiple cortical emboli occurred in six. Distal pathology of the ACA (n = 13) was the most frequent MRA finding. Core symptom was contralateral hemiparesis with lower limb predominance (n = 29), partly associated with early-onset spasticity. Interestingly, motor evoked potential recording was abnormal in only five patients. Further characteristic symptoms were psychomotor slowing (n = 9), often with speech disturbances such as decreased verbal fluency, and confusional state (n = 4). Visual or motor hemineglect (n = 5) as well as apraxia (n = 5) was confined to a few patients only. Pericallosal artery infarctions are a rare localization of stroke, mostly occurring as partial infarctions due to distal ACA pathology. Clinically, they are mainly characterized by hemiparesis predominately in the lower limb caused by involvement of supplementary motor cortex areas without affection of the corticospinal tract.

Cerebral network disruption as a possible mechanism for impaired recovery after acute pontine stroke.

BACKGROUND: Recovery from stroke is presumed to be a function of a widespread cerebral network. Chronic white matter lesions (WML) have been proposed to be a predictor of poor outcome after acute stroke. We tested the hypothesis that the extent of WML has an effect on functional recovery in acute pontine stroke by disrupting the integrity of the supratentorial cerebral network. METHODS: Seventeen patients with acute unilateral pontine stroke who had received a standardized stroke workup and additional diffusion tensor imaging (DTI) were studied. After grading the extent of WML according to the Fazekas scale and semiautomated lesion volume calculation, we compared patients with acute pontine infarction and advanced WML to those with absent or minimal WML regarding baseline characteristics, stroke subtype and clinical outcome. In addition, we used tract-based spatial statistics for voxel-wise analysis of the DTI-derived parameter fractional anisotropy in the white matter tracts. RESULTS: The volume of WML ranged between 0.1 and 42.1 cm³ (mean = 15.9) and was graded as follows: 0 in 5.9%, 1 in 35.3%, 2 in 41.2% and 3 in 17.6%. Both patients with Fazekas grades 2-3 (p = 0.014) as well as those with larger WML volumes (p = 0.037) had severer functional deficits at the 3-month follow-up. White matter tracts displaying a significant decrease in fractional anisotropy values were the corpus callosum, the anterior thalamic radiation and the inferior fronto-occipital fasciculus. CONCLUSIONS: Chronic WML contribute to a less favorable clinical outcome after pontine stroke depending on (1) the extent of pre-existing WML and (2) the degree of disruption of cerebral connectivity as indicated by reduced tissue integrity in the white matter not affected by WML as detected by DTI and tract-based spatial statistics.

Loss of callosal fibre integrity in healthy elderly with age-related white matter changes.

Age-related white matter changes (ARWMC) appear to correspond to a continuum from normal functioning to clinically overt neurological syndromes. Disturbance of the structural integrity of cerebral fibre tracts-the so-called cerebral network-by ARWMC might be one explanation for this development. From 3 T magnetic resonance imaging (MRI) data of 34 healthy elderly subjects (60-82 years) we calculated the lesion volume of ARWMC and the area of the corpus callosum (CC). Gait, balance and cognition were assessed. We compared these findings in those with mild (n = 22) and advanced (n = 12) ARWMC and performed tract-based spatial statistics (TBSS) to analyze white matter structural integrity. In subjects with advanced ARWMC, TBSS showed a significant decrease of fractional anisotropy (FA) in several large tracts of the white matter including the CC; total CC, CC2 and CC5 areas were significantly smaller. Despite these morphological changes, tests of gait, balance and cognition as measured by the Mini-Mental State Examination (MMSE) were in the normal range for both groups; only the Montreal Cognitive Assessment (MoCA) detected executive and language dysfunction in those with advanced ARWMC. Loss of tissue integrity and atrophy of the CC secondary to spatially remote lesions in the peri- and paraventricular white matter in ARWMC appear to be already detectable in healthy elderly individuals.

Deviations from the diffusion tensor model as revealed by contour plot visualization using high angular resolution diffusion-weighted imaging (HARDI).

The standard diffusion tensor model is limited in its ability to provide detailed information about multidirectional fiber architecture in human white matter. Additional directional acquisition of diffusivity properties with high angular resolution diffusion-weighted imaging (HARDI) acquisition schemes may deliver more information on areas with fiber crossings than standard DTI. However, representation of the additional information and the rating and visualization of fiber complexity is challenging. We used projection 2D-plots in combination with a HARDI acquisition scheme of 129 diffusion directions and compared the spherical diffusion variance index (SDI) with the relative anisotropy index (RAI). In normal controls, white matter areas with unidirectional fiber arrangement and areas with more complex fiber composition were identified with this approach. HARDI confirms and can visualize deviations from the tensor-like representation, thereby providing information on fiber structure complexity, which may be of considerable interest for clinical studies.