Diffusion tensor imaging analysis with tract-based spatial statistics of the white matter abnormalities after epilepsy surgery.

INTRODUCTION: Diffusion tensor imaging (DTI) techniques demonstrated diffuse bilateral temporal and extra-temporal abnormalities of white matter in patients presenting mesial temporal lobe epilepsy with hippocampal sclerosis (HS). The aim of this study was to assess these diffusion changes following temporal lobe surgery, by applying a novel voxel-based tract-based spatial statistics (TBSS) technique for whole-brain analysis of fractional anisotropy (FA) and mean diffusivity (MD). Second, region-of-interest analysis (ROI) was performed to improve statistical power. MATERIAL AND METHODS: The study included 22 patients with unilateral HS. Twelve patients underwent temporal lobe surgery. Follow up MRI was done in a mean interval of 4 months. Voxelwise pre-operative FA asymmetry in all 22 patients was assessed within subjects between lesional and contralateral hemispheres. The whole-brain post-operative dataset of 10 seizure-free patients was compared with the corresponding pre-operative dataset using voxel-wise statistical analysis. Additionally, regional analysis at the fornices was done with skeleton-based region of interest (SROI). RESULTS: Within a mean interval time of 6.3 months after surgery, 10 of 12 patients were seizure free (83.3%). The voxelwise comparison between lesional and contralateral hemispheres was consistent with previous studies showing a more widespread diffusion alteration in the lesional hemisphere. Voxel-wise comparison between post and pre-operative dataset did not show supra-thresholded voxels. SROI statistical analysis showed significant decrease in FA and increase in MD in the ipsilateral fornix. Significant increase in FA was observed in the contralateral fornix after surgery. CONCLUSION: The ipsi-lesional fornix showed decreased FA and increased MD after surgery, consistent with Wallerian degeneration. In contrast, contra-lesional fornix demonstrated increase in FA. This observation is important for our understanding of the fate of the remaining brain tissue following removal of an epileptic focus. Postoperative increase in FA may reflect structural reorganization in response to epilepsy surgery. The discrepancy between SROI and voxelwise statistics emphasizes the difference of statistical sensitivity between voxelwise and ROI analyses.

The corpus callosum: white matter or terra incognita.

The corpus callosum is the largest white matter structure in the brain, consisting of 200-250 million contralateral axonal projections and the major commissural pathway connecting the hemispheres of the human brain. The pathology of the corpus callosum includes a wide variety of entities that arise from different causes such as congenital, inflammatory, tumoural, degenerative, infectious, metabolic, traumatic, vascular and toxic agents. The corpus callosum, or a specific part of it, can be affected selectively. Numerous pathologies of the corpus callosum are encountered during CT and MRI. The aim of this study is to facilitate a better understanding and thus treatment of the pathological entities of the corpus callosum by categorising them according to their causes and their manifestations in MR and CT imaging. Familiarity with its anatomy and pathology is important to the radiologist in order to recognise its disease at an early stage and help the clinician establish the optimal therapeutic approach.

Late adult onset of Langerhans cell histiocytosis mimicking glioblastoma multiforme.

Langerhans cell histiocytosis (LCH) with multiple organ involvement is a rare disorder in adults. Extrapituitary involvement of the central nervous system (CNS) is uncommon. We report the unusual case of a 55-year-old woman presenting with a left-sided hemiataxia-hemiparesis, left hemisensory loss and short-lasting episodes of an alien left hand due to lesions of the internal capsule and the right thalamus, extending into the mesencephalon associated with extensive surrounding edema, without pituitary involvement. The neuroradiological image suggested glioblastoma multiforme. Brain biopsy revealed inflammatory tissue and "pseudotumoral" multiple sclerosis was suspected. Biopsy of concomitant lung and bone lesions disclosed Langerhans cell histiocytosis. The treatment with pulsed steroids in association with mycophenolate mofetil led to a sustained, clinical neurological remission.

New approaches in imaging of the brachial plexus.

Imaging plays an essential role for the detection and analysis of pathologic conditions of the brachial plexus. Currently, several new techniques are used in addition to conventional 2D MR sequences to study the brachial plexus: the 3D STIR SPACE sequence, 3D heavily T2w MR myelography sequences (balanced SSFP=CISS 3D, True FISP 3D, bFFE and FIESTA), and the diffusion-weighted (DW) neurography sequence with fiber tracking reconstruction (tractography). The 3D STIR sequence offers complete anatomical coverage of the brachial plexus and the ability to slice through the volume helps to analyze fiber course modification and structure alteration. It allows precise assessment of distortion, compression and interruption of postganglionic nerve fibers thanks to the capability of performing maximum intensity projections (MIP) and multiplanar reconstructions (MPRs). The CISS 3D, b-SSFP sequences allow good visualization of nerve roots within the spinal canal and may be used for MR myelography in traumatic plexus injuries. The DW neurography sequence with tractography is still a work in progress, able to demonstrate nerves tracts, their structure alteration or deformation due to pathologic processes surrounding or located along the postganglionic brachial plexus. It may become a precious tool for the understanding of the underlying molecular pathophysiologic mechanisms in diseases affecting the brachial plexus and may play a role for surgical planning procedures in the near future.

Interictal arterial spin-labeling MRI perfusion in intractable epilepsy.

INTRODUCTION: Magnetic resonance imaging (MRI) is required for the investigation of surgically intractable epilepsy. In addition to the standard MRI techniques, perfusion sequences can be added to improve visualization of underlying pathological changes. Arterial spin-labeling (ASL) MRI perfusion does not require contrast administration and, for this reason, may have advantages in these patients. METHODS: We report here on 16 patients with epilepsy who underwent MRI of the brain with ASL and positron emission tomography (PET). RESULTS: Despite a slightly reduced resolution with ASL, we found a correlation between ASL, PET and electrophysiological data, with hypoperfusion on ASL that corresponded with hypoperfusion on interictal PET. CONCLUSION: Given the correlation between ASL and PET and electrophysiology, perfusion with ASL could become part of the standard work-up in patients with epilepsy.

Presentación cerebelosa atípica de la encefalopatía de Wernicke / Unusual cerebellar presentation of Wernicke’s encephalopathy

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Mielinólisis central pontina: criterios diagnósticos en resonancia magnética / Central pontine myelinolysis: MR findings

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Brain and spine MRI artifacts at 3Tesla.

INTRODUCTION: We illustrate here the most common MRI artifacts found on routine 3T clinical neuroradiology that can simulate pathology and interfere with diagnosis. MATERIALS AND METHODS: Our group has worked with a 3-T Magnetom Trio (Siemens, Erlangen, Germany) system for two years, with 50% of our time devoted to clinical work and 50% dedicated to research; 65% of the clinical time is dedicated to neuroradiology (2705 patients) and the remaining time to whole-body MRI. We have detected these artifacts during our case readings and have selected the most representative of each type to illustrate here. RESULTS: We have observed magnetic susceptibility artifacts (29%), pulsation artifacts (57%), homogeneity artifacts (3%), motion artifacts (6%), truncation artifacts (3%) and, finally, artifacts due to poor or inadequate technique in the examined region. CONCLUSION: High-field imaging offers the benefit of a higher signal-to-noise ratio, thus making possible the options of a higher imaging matrix, thinner slices, the use of spectroscopy and diffusion tensor imaging in the routine clinical neuroradiology with a reduction in time spent. It is vital to be able to recognize these artifacts in everyday practice as they can mimic pathological appearances, thus causing diagnostic errors that could lead to unnecessary treatment. Indeed, most of these artifacts could be avoided with an adequate technique.

Postictal deficit mimicking stroke: role of perfusion CT.

OBJECTIVES: To demonstrate the use of perfusion CT in patients presenting with a suspected diagnosis of stroke to avoid the administration of inappropriate thrombolytic therapy in stroke-mimicking conditions such as status epilepticus. MATERIAL AND METHODS: We reviewed the imaging studies of four patients presenting with symptoms suggestive of stroke, but finally diagnosed with status epilepticus. Imaging was by a 16-section multidetector CT scanner using a protocol consisting of non-contrast CT, CT angiography and perfusion CT. Color-coded maps allowed calculation of the CBV (cerebral blood volume), CBF (cerebral blood flow) and MTT (mean transit time). RESULTS: In all four cases, perfusion CT revealed increases in CBF and CBV as well as a decreased MTT, consistent with hyperperfusion linked to status epilepticus with focal deficit-in contrast to the hypoperfusion observed in stroke patients. CONCLUSION: The use of perfusion CT accurately detected hyperperfusion in status epilepticus presenting as stroke. In such cases, perfusion CT imaging avoided the administration of potentially harmful thrombolytic therapy to patients experiencing seizures due to different underlying etiologies.

Evaluation of perfusion CT and TIBI grade in acute stroke for predicting thrombolysis benefit and clinical outcome.

OBJECTIVE: To evaluate the prognostic accuracy of combining perfusion CT (PCT) and thrombolysis in brain ischemia (TIBI) ultrasonographic grade in the triage of stroke patients who will benefit from thrombolysis and in predicting the clinical outcome. METHODS: We conducted a prospective study of all consecutive stroke patients admitted to our hospital from March 2003 to July 2007, presenting with signs of acute stroke within the therapeutic window, who had undergone either intravenous or combined intravenous and intra-arterial thrombolysis. All patients were evaluated by a complete stroke CT protocol, transcranial color-coded duplex sonographic monitoring, follow-up imaging (CT or MRI) and clinical outcome at 3 months, as assessed by the modified Rankin scale (mRS). RESULTS: A total of 34 patients were included with a mean NIHSS on admission of 14.2. This study revealed that PCT had 95% sensitivity and 71% specificity in the evaluation of therapy benefit as well as 75% sensitivity and 39% specificity in predicting clinical outcome. The extent of ischemic tissue according to PCT and TIBI grade were significantly correlated (p<0.05). Using the MTT-TTP approach was an alternative to the classical MTT-CBV approach for determining tissue at risk. The clinical outcome assessed by the mRS was considered favorable (mRS 0-2) in 16 patients and unfavorable (mRS>2) in 18 patients. CONCLUSION: PCT was the most accurate predictor of both thrombolytic therapy benefit and clinical outcome. The TIBI score was useful for determining whether or not to perform intravenous therapy alone or as a combined therapy.

"Gourmand syndrome" in a child with pharmacoresistant epilepsy.

We report the case of a 10-year-old boy with pharmacoresistant epilepsy, symptomatic of a right temporoparietal hemorrhagic lesion, who displayed an eating passion as described for the gourmand syndrome (GS) in adults and discuss the role of epilepsy in GS. This patient presented with a significant change in his eating habits (abnormal preoccupation with the preparation and eating of fine-quality food) concordant with the onset of his seizure disorder, without any previous history of eating disorders or psychiatric illness. This observation corroborates the important role of the right cerebral hemisphere in disturbed eating habits, including the relatively benign GS, and, possibly rarely, in less benign eating disorders such as anorexia and obesity.

Neuro-imaging of cerebral ischemic stroke.

Major progress has recently been made in the neuro-imaging of stroke as a result of improvements in imaging hardware and software. Imaging may be based on either magnetic resonance imaging (MRI) or computed tomography (CT) techniques. Imaging should provide information on the entire vascular cervical and intracranial network, from the aortic arch to the circle of Willis. Equally, it should also give information on the viability of brain tissue and brain hemodynamics. CT has the advantage in the detection of acute hemorrhage whereas MRI offers more accurate pathophysiological information in the follow-up of patients.

High-resolution and functional magnetic resonance imaging of the brachial plexus using an isotropic 3D T2 STIR (Short Term Inversion Recovery) SPACE sequence and diffusion tensor imaging.

This technical note demonstrates the relevance of the isotropic 3D T2 turbo-spin-echo (TSE) sequence with short-term inversion recovery (STIR) and variable flip angle RF excitations (SPACE: Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) for high-resolution brachial plexus imaging. The sequence was used in 11 patients in the diagnosis of brachial plexus pathologies involving primary and secondary tumors, and in six volunteers. We show that 3D STIR imaging is not only a reliable alternative to 2D STIR imaging, but it also better evaluates the anatomy, nerve site compression and pathology of the plexus, especially to depict space-occupying tumors along its course. Finally, due to its appropriate contrast we describe how 3D-STIR can be used as a high-resolution mask to be fused with fraction of anisotropy (FA) maps calculated from diffusion tensor imaging (DTI) data of the plexus.

[Clinical findings, electroneuromyography and MRI in trauma of the brachial plexus]. / Aspects cliniques, électroneuromyographiques et IRM des traumatismes du plexus brachial.

OBJECTIVES: Management of traumatic lesions of the brachial plexus mainly depends on whether the injury is pre- (nerve root avulsion) or postganglionic (trunks and cords). The aim of this study was to assess the diagnostic and prognostic value of MRI in such lesions, and to determine any correlations among radiological, clinical and electroneuromyographical (EMG) data from both the initial and follow-up studies. MATERIAL AND METHODS: Nine patients with acute traumatic lesions of the brachial plexus were investigated by MRI and EMG. Five further patients served as controls. The MRI protocol included fast spin-echo (FSE) T2-weighted and STIR sequencing. These scans were independently interpreted by two senior radiologists. Their findings were then validated during consensus meetings of surgeons, radiologists and neurologists to identify the exact localization and mechanism of each lesion, and to determine the advantages and drawbacks of each technique. RESULTS: Among the nine patients, MRI scans were judged as normal in three whereas EMG showed distal lesions in two of them. In a further three patients, STIR MRI sequences demonstrated high signal intensities from the trunks and cords of C5 to T1. Among these three patients, MRI at three months showed persistence of these signal anomalies in one patient, and partial regression in the two others. In the remaining three patients, three-dimensional T2-weighted sequences showed nerve root avulsion, consistent with the initial EMG findings. CONCLUSION: MRI is the best technique to demonstrate nerve root avulsion. However, unlike EMG, MRI does not allow visualization of distal lesions of the brachial plexus. Differentiation between edema (reversible) and demyelination (irreversible) of trunk and cord lesions remains difficult, and requires EMG or late MRI.