S. Kremer

Use of Advanced Magnetic Resonance Imaging Techniques in Neuromyelitis Optica Spectrum Disorder.

Brain parenchymal lesions are frequently observed on conventional magnetic resonance imaging (MRI) scans of patients with neuromyelitis optica (NMO) spectrum disorder, but the specific morphological and temporal patterns distinguishing them unequivocally from lesions caused by other disorders have not been identified. This literature review summarizes the literature on advanced quantitative imaging measures reported for patients with NMO spectrum disorder, including proton MR spectroscopy, diffusion tensor imaging, magnetization transfer imaging, quantitative MR volumetry, and ultrahigh-field strength MRI. It was undertaken to consider the advanced MRI techniques used for patients with NMO by different specialists in the field. Although quantitative measures such as proton MR spectroscopy or magnetization transfer imaging have not reproducibly revealed diffuse brain injury, preliminary data from diffusion-weighted imaging and brain tissue volumetry indicate greater white matter than gray matter degradation. These findings could be confirmed by ultrahigh-field MRI. The use of nonconventional MRI techniques may further our understanding of the pathogenic processes in NMO spectrum disorders and may help us identify the distinct radiographic features corresponding to specific phenotypic manifestations of this disease.

Diffusion tensor imaging of normal-appearing white matter in neuromyelitis optica.

OBJECTIVES Neuromyelitis optica (NMO) is an inflammatory disease of the central nervous system characterized by severe attacks of optic neuritis and myelitis. Brain was classically, unlike in multiple sclerosis (MS), spared. Nevertheless recent studies showed that brain lesions can be seen with MRI. We studied the diffusion characteristics of normal-appearing white matter (NAWM) and abnormal white matter in NMO patients compared with NAWM in healthy subjects. PATIENTS AND METHODS Diffusion tensor imaging (DTI) scans of the brain and spinal cord were obtained from 25 patients with NMO and 20 age- and gender-matched healthy subjects. Region of interest (ROI) analysis of the apparent diffusivity coefficient (ADC) and fractional anisotropy (FA) was performed in brain NAWM (optic radiations, corpus callosum [CC] and anterior and posterior limbs of the internal capsule [IC]) and in spinal cord NAWM and in lesions. RESULTS ADC was increased and FA decreased in NMO patients in the posterior limb of the IC in the optic radiations and in spinal cord NAWM. FA was lower in spinal cord lesions. In contrast, there was no difference between the two groups in the anterior limb of the IC nor in the CC. CONCLUSION These results suggest that DTI abnormalities are very severe in NMO spinal cord lesions. In our study, DTI abnormalities in NAWM were restricted to optic radiations and cortico-spinal tracts, suggesting secondary Wallerian degeneration. In contrast, NAWM outside these tracts (CC and anterior IC) remained normal suggesting that, unlike what is observed in MS, there is no infra-lesional abnormality in NMO.

Brain lesion distribution criteria distinguish MS from AQP4-antibody NMOSD and MOG-antibody disease.

Importance Neuromyelitis optica spectrum disorders (NMOSD) can present with very similar clinical features to multiple sclerosis (MS), but the international diagnostic imaging criteria for MS are not necessarily helpful in distinguishing these two diseases. Objective This multicentre study tested previously reported criteria of ‘(1) at least 1 lesion adjacent to the body of the lateral ventricle and in the inferior temporal lobe; or (2) the presence of a subcortical U-fibre lesion or (3) a Dawsons finger-type lesion’ in an independent cohort of relapsing-remitting multiple sclerosis (RRMS) and AQP4-ab NMOSD patients and also assessed their value in myelin oligodendrocyte glycoprotein (MOG)-ab positive and ab-negative NMOSD. Design Brain MRI scans were anonymised and scored on the criteria by 2 of 3 independent raters. In case of disagreement, the final opinion was made by the third rater. Participants 112 patients with NMOSD (31 AQP4-ab-positive, 21 MOG-ab-positive, 16 ab-negative) or MS (44) were selected from 3 centres (Oxford, Strasbourg and Liverpool) for the presence of brain lesions. Results MRI brain lesion distribution criteria were able to distinguish RRMS with a sensitivity of 90.9% and with a specificity of 87.1% against AQP4-ab NMOSD, 95.2% against MOG-ab NMOSD and 87.5% in the heterogenous ab-negative NMOSD cohort. Over the whole NMOSD group, the specificity was 89.7%. Conclusions This study suggests that the brain MRI criteria for differentiating RRMS from NMOSD are sensitive and specific for all phenotypes.

Foreign accent syndrome as a first sign of multiple sclerosis

Background Foreign accent syndrome (FAS) consists of a speech rhythm disorder different from dysarthia or aphasia. It is unusually met in multiple sclerosis (MS). Objective We report a case of FAS as an initial symptom of a MS. Methods A right-handed French woman developed an isolated German foreign accent. Brain magnetic resonance imaging (MRI), SPECT and analysis of CSF were performed. Results Brain MRI revealed a large hypersignal on T2-weighted images in the left prerolandic white matter. Single photon emission computed tomography showed a right prerolandic hypoperfusion. Unmatched oligoclonal bands in cerebrospinal fluid and occurrence of new abnormal hypersignals on the following MRI led us to diagnose MS. Conclusion FAS may be the first symptom of MS. It could result from extensive disturbances of brain function involving the right hemisphere.

Imagerie des lésions kystiques du canal rachidien chez l’adulte

Resume Les lesions kystiques intrarachidiennes sont frequentes, sous tendant des etiologies tres variees. Elles peuvent etre classees en fonction de leur localisation en lesions kystiques intra medullaires et lesions kystiques extramedullaires. Dans ces 2 categories elles peuvent etre ensuite regroupees en fonction du tissu a partir duquel elles se developpent. L’IRM est l’examen de choix pour permettre l’etude du contenu intracanalaire et le diagnostic differentiel entre ces differentes lesions.

Espaces rachidiens intracanalaires : de l’anatomie radiologique au diagnostic étiologique

The spinal canal is divided into epidural, subdural and subarachnoid spaces. Intraspinal processes should be correctly placed into their space of origin. MRI is the best imaging modality to achieve this task. Accurate determination of the space of origin routinely requires the acquisition of two different pulse sequences, typically T1W and T2W images, in two orthogonal planes, usually axial and sagittal. Simple imaging features can assist in determining the site of origin: changes to the epidural fat, compression or widening of subarachnoid spaces. The epidural space, bordered medially by dura, contains fat and vascular structures. The subdural space is a virtual space in between the dura and arachnoid membrane. The subarachnoid space is home to the CSF, spinal cord and nerve rootlets. An epidural process replaces the epidural fat, displaces the dura and narrows the subarachnoid space. A subarachnoid process widens the subarachnoid space and spares the epidural fat. Epidural processes usually are infectious or tumoral, either primary or secondary to spinal involvement. Subarachnoid processes include primary tumors, leptomeningeal metastases, arachnoiditis and hemorrhage. Nerve sheath tumors and meningiomas are the most frequent intradural extramedullary tumors.

Reorientation strategies for High Order Tensors

In Diffusion Magnetic Resonance Imaging, the diffusion process is commonly modeled by a symmetric 2nd order tensor. Since 2nd order tensors are not able to properly model crossing fibers, High Order Tensors (HOTs) can be considered in particular to model the Orientation Distribution Function. Applying a spatial transformation to such tensor fields requires an appropriate reorientation strategy to preserve the relevancy of the orientational information related to fiber organization. We propose a general framework for HOT reorientation, relying on the decomposition of an HOT as a function of several 2nd order tensors. Contrary to existing methods, this approach enables to reorient fibers from a crossing independently. Experiments on simulated data highlight the benefit of the proposed method.

Comparison of interpolation methods for angular resampling of diffusion weighted images

Diffusion Magnetic Resonance Imaging (DMRI) is an emerging technique permitting to visualize the neuronal architecture of brain white matter by measuring the diffusion of water molecules in tissues. A DMRI acquisition is composed of a collection of diffusion weighted images (DWIs) that characterize the diffusion property in several noncolinear directions. Resampling such acquisitions to obtain measures of diffusion in other directions is a problem that may arise when registering or comparing DWIs. In this paper, we present a comparison of several spherical interpolation schemes for DWIs. Numerical experiments are achieved on both synthetic and real data.

IRM de diffusion dans les myelopathies non compressives : a propos de 32 patients

Objectifs Notre travail etait d’evaluer l’apport de la sequence de diffusion en IRM et du calcul du coefficient apparent de diffusion (ADC) dans le diagnostic etiologique des myelopathies non compressives. Materiels et methodes Trente-deux patients souffrant de myelopathies non compressives ont beneficie entre septembre 2005 et novembre 2007 d’une IRM medullaire avec sequence de diffusion. Pour chaque patient, l’ADC a ete calcule dans la moelle pathologique. Des calculs en moelle saine ont ete realises chez dix patients temoins. Les resultats des differents sous-groupes ont ete compares selon un test de Student. Resultats Quinze patients presentaient une myelopathie d’origine inflammatoire dont neuf sclerose en plaques. Six patients presentaient une myelopathie para-infectieuse, cinq patients une ischemie medullaire et six patients des etiologies autres. L’ADC etait significativement plus eleve dans la moelle pathologique des patients presentant une atteinte inflammatoire ou para-infectieuse que dans la moelle saine ou dans la moelle ischemique. Il n’existait pas de difference significative entre les valeurs d’ADC des patients presentant une pathologie inflammatoire et celles des patients presentant une atteinte para-infectieuse. Conclusion Ces resultats sont importants pour differencier les myelopathies ischemiques des myelopathies inflammatoires ou para-infectieuses. Les calculs restent parfois limites par les qualites techniques de la sequence.

Syndrome medullaire et/ou radiculaire aigu

Objectifs Connaitre les principales pathologies et les symptomes radiculaires et medullaires qui necessitent le recours a l’imagerie en urgence. Connaitre la technique d’imagerie la plus efficace en fonction de la situation clinique. Savoir optimiser la technique d’imagerie en fonction de la pathologie recherchee et savoir eviter certains pieges lors de l’interpretation (artefacts de flux, fausses collections epidurales…). Points cles L’IRM est la methode de reference pour le diagnostic de la plupart des syndromes medullaires. L’IRM et la scanographie sont efficaces pour determiner l’etiologie d’un syndrome radiculaire aigu deficitaire de nature compressive. Les indications et les delais de realisation des examens d’imagerie pour une lombosciatique commune doivent respecter les recommandations de l’ANAES-HAS. Le diagnostic etiologique de la plupart des myelopathies aigues necessite une correlation des donnees de l’imagerie a celles du bilan clinique et biologique. Resume L’IRM est l’examen de premiere intention a realiser en cas de syndrome medullaire aigu. Les etiologies compressives s’installent le plus souvent progressivement, mais peuvent decompenser brutalement. Les etiologies compressives les plus frequentes sont liees a des lesions extradurales (metastases vertebrales, hematome extradural spontane) ; les compressions d’origine intradural (meningiome, neurinome, ependymome de la queue de cheval) ne se revelent de maniere aigue qu’en cas de complication hemorragique ou ischemique ou dans les suites d’un traumatisme ; il en va de meme des tumeurs intramedullaires. Les myelopathies aigues (ischemie, myelite…) se traduisent habituellement par un signal hyperintense intramedullaire en T2, parfois associe a un elargissement medullaire et a une prise de contraste. La semiologie IRM et la correlation au tableau clinique et paraclinique (analyse du LCS…) permettent d’orienter le diagnostic etiologique. La confrontation aux donnees de la scanographie peut etre utile en cas de compression par une lesion tumorale vertebrale. En cas de contre-indication a l’IRM, une exploration scanographique rachidienne localisee ou etendue a l’ensemble du rachis, permet de deceler certaines etiologies compressives (metastase rachidienne, hematome extradural). La scanographie et l’IRM permettent des performances similaires pour la mise en evidence d’une compression, notamment d’origine discale en cas de syndrome radiculaire aigu. Le bilan scanographique negatif d’une atteinte radiculaire aigue, notamment deficitaire, peut necessiter une 1RM complementaire. Le syndrome de la queue de cheval necessite le recours a l’IRM en urgence.