Jacques Chiras

Memory disorders in probable Alzheimer's disease: the role of hippocampal atrophy as shown with MRI.

Magnetic resonance based volumetric measures of hippocampal formation, amygdala (A), caudate nucleus (CN), normalised for total intracranial volume (TIV), were analysed in relation to measures of cognitive deterioration and specific features of memory functions in 18 patients with probable Alzheimers disease. Neuropsychological examination included the mini mental state examination (MMSE), the Mattis dementia rating scale (DRS), tests of executive functions, assessment of language abilities and praxis, the Wechsler memory scale (WMS), the California verbal learning test (CVLT) and the Grober and Buschke test. The volume of the hippocampal formation (HF/TIV) was correlated with specific memory variables: memory quotient and paired associates of the WMS; intrusions and discriminability at recognition for the Grober and Buschke test. By contrast, except for intrusions, no correlations were found between memory variables and the volume of amygdala (A/TIV). No correlations were found between the volume of caudate nuclei (CN/TIV) and any neuropsychological score. The volume of the hippocampal formation was therefore selectively related to quantitative and qualitative aspects of memory performance in patients with probable Alzheimers disease.

Diffusion tensor imaging in medial temporal lobe epilepsy with hippocampal sclerosis

Interictal diffusion imaging studies in patients with medial temporal lobe epilepsy (MTLE) accompanied by hippocampal sclerosis (HS) have shown an increased diffusivity in the epileptogenic hippocampus. In this study, we wanted to explore the whole brain in order to determine if MTLE could have an impact on the organization and the architecture of a large cerebral network and to identify clinical factors that could mediate diffusion abnormalities. Diffusion tensor imaging (DTI) and statistical parametric mapping of the entire brain were performed in 35 well-defined MTLE patients and in 36 healthy volunteers. SPM analyses identified three abnormal areas: an increased diffusivity was detected in the epileptic hippocampus and the ipsilateral temporal structures associated with a decreased anisotropy along the temporal lobe, a decreased diffusivity was found in the contralateral non-sclerotic hippocampus, the amygdala, and the temporal pole, and finally, a decreased anisotropy was noted ipsilaterally in posterior extratemporal regions. Duration of epilepsy, age at onset, and the frequency of generalized tonic-clonic seizures or partial complex seizures did not correlate with the presence of diffusion abnormalities. Region of interest analysis in the hippocampus/parahippocampus demonstrated a correlation between lower ipsilateral diffusivity values and occurrence of epigastric aura and between higher anisotropy values in both hemispheres and history of febrile seizures. In conclusion, this study showed that diffusion abnormalities are not restricted to the pathologic hippocampus and involve a larger network. This pattern may indirectly reflect the epileptogenic network and may be interpreted as a cause or a consequence of epilepsy.

Comparison of diffusion tensor imaging tractography of language tracts and intraoperative subcortical stimulations

OBJECT Diffusion tensor (DT) imaging tractography is increasingly used to map fiber tracts in patients with surgical brain lesions to reduce the risk of postoperative functional deficit. There are few validation studies of DT imaging tractography in these patients. The aim of this study was to compare DT imaging tractography of language fiber tracts by using intraoperative subcortical electrical stimulations. METHODS The authors included 10 patients with low-grade gliomas or dysplasia located in language areas. The MR imaging examination included 3D T1-weighted images for anatomical coregistration, FLAIR, and DT images. Diffusion tensors and fiber tracts were calculated using in-house software. Four tracts were reconstructed in each patient including the arcuate fasciculus, the inferior occipitofrontal fasciculus, and 2 premotor fasciculi (the subcallosal medialis fiber tract and cortical fibers originating from the medial and lateral premotor areas). The authors compared fiber tracts reconstructed using DT imaging with those evidenced using intraoperative subcortical language mapping. RESULTS Seventeen (81%) of 21 positive stimulations were concordant with DT imaging fiber bundles (located within 6 mm of a fiber tract). Four positive stimulations were not located in the vicinity of a DT imaging fiber tract. Stimulations of the arcuate fasciculus mostly induced articulatory and phonemic/syntactic disorders and less frequently semantic paraphasias. Stimulations of the inferior occipitofrontal fasciculus induced semantic paraphasias. Stimulations of the premotor-related fasciculi induced dysarthria and articulatory planning deficit. CONCLUSIONS There was a good correspondence between positive stimulation sites and fiber tracts, suggesting that DT imaging fiber tracking is a reliable technique but not yet optimal to map language tracts in patients with brain lesions. Negative tractography does not rule out the persistence of a fiber tract, especially when invaded by the tumor. Stimulations of the different tracts induced variable language disorders that were specific to each fiber tract.

Preoperative spinal cord arteriography in aneurysmal disease of the descending thoracic and thoracoabdominal aorta: preliminary results in 45 patients.

Between 1985 and 1988 45 patients with descending thoracic or thoracoabdominal aortic aneurysms underwent selective arteriography of the intercostal and lumbar arteries to delineate preoperatively the artery of Adamkiewicz and the thoracic radicular artery. Identification of these vessels failed in five patients (11%), was considered complete in 31 patients (69%) and incomplete in nine (20%). Selective arteriography classified these patients into four groups: groups A and B--the artery of Adamkiewicz arose respectively above and below the zone of operation; group C--the artery arose directly from the segment to be operated; and group D--origin could not be determined. All 30 patients in group C underwent a spinal cord revascularization procedure (complete in 20 cases, incomplete in 10). Spinal cord complications occurred in 9/45 patients (20%). No spinal cord complications occurred in groups A and B; their incidence was 5% in group C when revascularization was complete, and 50% when revascularization was incomplete; and 60% had complications in group D (p less than 0.01). Spinal cord complications were more frequent (p less than 0.05) when the artery of Adamkiewicz arose from an intercostal or lumbar artery obliterated at its aortic origin but filled through collaterals or when spinal cord circulation was interrupted for more than 45 minutes. This study confirms the importance of preserving arterial supply to the spinal cord during repair of descending thoracic and thoracoabdominal aneurysms. The information obtained from spinal cord arteriography allows the prediction of complications and informs the choice of the appropriate surgical technique.

Diffusion tensor imaging and voxel based morphometry study in amyotrophic lateral sclerosis: relationships with motor disability

The aim of this study was to investigate the extent of cortical and subcortical lesions in amyotrophic lateral sclerosis (ALS) using, in combination, voxel based diffusion tensor imaging (DTI) and voxel based morphometry (VBM). We included 15 patients with definite or probable ALS and 25 healthy volunteers. Patients were assessed using the revised ALS Functional Rating Scale (ALSFRS-R). In patients, reduced fractional anisotropy was found in bilateral corticospinal tracts, the left insula/ventrolateral premotor cortex, the right parietal cortex and the thalamus, which correlated with the ALSFRS-R. Increased mean diffusivity (MD) was found bilaterally in the motor cortex, the ventrolateral premotor cortex/insula, the hippocampal formations and the right superior temporal gyrus, which did not correlate with the ALSFRS-R. VBM analysis showed no changes in white matter but widespread volume decreases in grey matter in several regions exhibiting MD abnormalities. In ALS patients, our results show that subcortical lesions extend beyond the corticospinal tract and are clinically relevant.

Experience of diffusion tensor imaging and 1H spectroscopy for outcome prediction in severe traumatic brain injury: Preliminary results.

Objective: The objective of the study is to test whether multimodal magnetic resonance imaging can provide a reliable outcome prediction of the clinical status, focusing on consciousness at 1 year after severe traumatic brain injury (TBI). Design: Single center prospective cohort with consecutive inclusions. Setting: Critical Care Neurosurgical Unit of a university hospital. Patients: Forty-three TBI patients not responding to simple orders after sedation cessation and 15 healthy controls. Interventions: A multimodal magnetic resonance imaging combining morphologic sequences, diffusion tensor imaging (DTI), and 1H proton magnetic resonance spectroscopy (MRS) was performed 24 ± 11 days after severe TBI. The ability of DTI and MRS to predict 1-year outcome was assessed by linear discriminant analysis (LDA). Robustness of the classification was tested using a bootstrap procedure. Measurements and Main Results: Fractional anisotropy (FA) was computed as the mean of values at discrete brain sites in the infratentorial and supratentorial regions. The N-acetyl aspartate/creatine (NAA/Cr) ratio was measured in the thalamus, lenticular nucleus, insular cortex, occipital periventricular white matter, and pons. After 1 year, 19 (44%) patients had unfavorable outcomes (death, persistent vegetative state, or minimally conscious state) and 24 (56%) favorable outcomes (normal consciousness with or without functional impairments). Analysis of variance was performed to compare FA and NAA/Cr in the two outcome groups and controls. FA and MRS findings showed highly significant differences between the outcome groups, with significant variables by LDA being supratentorial FA, NAA/Cr (pons), NAA/Cr (thalamus), NAA/Cr (insula), and infratentorial FA. LDA of combined FA and MRS data clearly separated the unfavorable outcome, favorable outcome, and control groups, with no overlap. Unfavorable outcome was predicted with up to 86% sensitivity and 97% specificity; these values were better than those obtained with DTI or MRS alone. Conclusion: FA and NAA/Cr hold potential as quantitative outcome-prediction tools at the subacute phase of TBI.

Productive and perceptive language reorganization in temporal lobe epilepsy.

The aim of this work was to determine whether productive and perceptive language functions are differentially affected in homogeneous groups of epilepsy patients with right and left temporal lobe epilepsy (TLE). Eighteen patients with left TLE, 18 with right TLE, and 17 healthy volunteers were studied using fMRI during performance of three tasks assessing the productive and perceptive aspects of language (covert semantic verbal fluency, covert sentence repetition, and story listening). Hemispheric dominance for language was calculated in the frontal and temporal regions using laterality indices (LI). Atypical lateralization was defined as a right-sided LI (LI<-0.20) in the frontal lobes during the verbal fluency task or in the temporal lobes during the story listening task. Control subjects and right TLE patients demonstrated a strong left lateralization for language in the frontal lobes during the fluency task, whereas activation was less lateralized to the left hemisphere in left TLE patients, although the difference did not reach significance. In the story listening and the repetition tasks, activation was significantly more right sided in the temporal lobes of patients with left TLE. Atypical language representation was found in 19% of TLE patients (five left and two right TLE). The shift toward the right hemisphere was significantly larger in the temporal than the frontal lobes in patients with atypical language lateralization compared to TLE patients with a typical language lateralization. Neuropsychological performances of patients with atypical language patterns were better than those of patients with typical patterns, suggesting that this reorganization may represent a compensatory mechanism.

Radiographic findings in 37 cases of primary CNS lymphoma in immunocompetent patients

Abstract. Because of the increasing incidence of primary central nervous system lymphoma (PCNSL), it is essential to recognize this disease in order to start appropriate treatment. We present the characteristic CT and MRI features of this tumour. The findings of 32 CT and 31 MR of 37 immunocompetent patients with biopsy-proved PCNSL are reviewed. The main features are presented and analysed, and are discussed in comparison with proven literature data. Primary central nervous system lymphoma presents as supratentorial solitary lesions in approximately 80% of the patients and multiple lesions in 20%. In contrast to classical data, the lesions are located in deep structures only in one-third of the cases, and involve posterior fossa in 10% of cases. Most of the lesions are hyperdense or isodense (92%) on CT, hypointense or isointense on T1-weighted images, and only about 40% are hyperintense on T2-weighted images. Nearly all the lesions enhance, except after corticosteroid administration. They produce mild oedema and mass effect. Meningeal or ventricular enhancement are rare but suggestive. Calcification, haemorrhage or necrosis are scarce. Although PCNSL in immunocompetent patients have a variable CT and MR appearance, the imaging data often suggest the diagnosis.

Imaging of cerebellopontine angle lesions: an update. Part 2: intra-axial lesions, skull base lesions that may invade the CPA region, and non-enhancing extra-axial lesions

Computed tomography (CT) and magnetic resonance (MR) imaging reliably demonstrate typical features of vestibular schwannomas or meningiomas in the vast majority of mass lesions responsible for cerebellopontine angle (CPA) syndrome. However, a large variety of unusual lesions can also be encountered in the CPA. Covering the entire spectrum of lesions potentially found in the CPA, these articles explain the pertinent neuroimaging features that radiologists need to know to make clinically relevant diagnoses in these cases, including data from diffusion- and perfusion-weighted imaging or MR spectroscopy, when available. A diagnostic algorithm based on the lesion’s site of origin, shape and margins, density, signal intensity and contrast material uptake is also proposed. Non-enhancing extra-axial CPA masses are cystic (epidermoid cyst, arachnoid cyst, neurenteric cyst) or contain fat (dermoid cyst, lipoma). Tumours can also extend into the CPA by extension from the skull base (paraganglioma, chondromatous tumours, chordoma, cholesterol granuloma, endolymphatic sac tumour). Finally, brain stem or ventricular tumours can present with a significant exophytic component in the CPA that may be difficult to differentiate from an extra-axial lesion (lymphoma, hemangioblastoma, choroid plexus papilloma, ependymoma, glioma, medulloblastoma, dysembryoplastic neuroepithelial tumour).

MRI features of neurodegenerative Langerhans cell histiocytosis

CNS complications of LCH include “space occupying” lesions corresponding to histiocytic granulomas and “neurodegenerative” presentation (ND-LCH) characterized by a progressive cerebellar ataxia. Studies analyzing specifically the MRI presentation of ND-LCH are scarce. We present here the MRIs of 13 patients registered as isolated ND-LCH. Posterior fossa was involved in 12 patients (92%), showing a symmetrical T2 hyperintensity of the cerebellar white matter areas in seven cases with a circumscribed T1 hyperintensity of the dentate nuclei in five cases, definite hyperintense T2 areas in the adjacent pontine tegmentum white matter in nine cases associated with a hyperintensity of the pontine pyramidal tracts in four cases. A cerebellar atrophy was noted in eight cases. The supratentorial region was involved in 11 patients, showing T2 hyperintense lesions in the cerebral white matter in eight cases and a discrete symmetrical T1 hyperintense signal in the globus pallidus in eight patients. A diffuse cortical atrophy was present in three cases and a marked focal atrophy of the corpus callosum in three cases. This series allows us to establish a not previously reported evocative semeiologic MR presentation to precisely orientate to the diagnosis of the pure neurodegenerative form of LCH.