Bilateral wallerian degeneration of the middle cerebellar peduncles due to unilateral pontine infarction.

We report the case of a patient with bilateral and symmetrical T2 hyperintensities of the middle cerebellar peduncles. She had a history of left pontine infarction 8 months before. This was attributed to bilateral Wallerian degeneration. MR Spectroscopy showed decreased N-acetyl aspartate/Creatine (NAA/Cr) ratio in the cerebellar peduncles as well as in the whole cerebellum. We hypothesize that this could reflect neuronal degeneration following a stroke.

[Paraneoplastic limbic encephalitis associated with epidermoid lung carcinoma]. / Encéphalite limbique paraneoplasique et carcinome épidermoide du poumon.

Paraneoplastic limbic encephalitis is a rare clinical entity, most often associated with small cell lung cancer. We report a case of a 54-year-old man presenting status epilepticus, cognitive dysfunction and loss of short term memory associated with epidermoid lung carcinoma. CT scan was normal whereas MRI revealed hyperintensities on T2WI and FLAIR images in the temporolimbic regions. Treatment of the primary tumour was followed by neurological improvement.

[Imaging of cerebral ischemia within first hours: computed tomography (CT)]. / Imagerie de l'ischémie cérébrale dans les premières heures: scanner.

Imaging of stroke has evolved with the development of stroke units and the CE approval of intravenous thrombolysis in the first three hours after stroke onset. The goal of imaging in the acute phase of stroke is: to make the diagnosis of stroke; to rule out other diagnosis (above all hemorrhagic strokes); to precise the location of the arterial occlusion; to assess the level of hypoperfusion; to evaluate the viability and reversibility of brain lesions; to understand the origin of the stroke by evaluating cervical arteries. Constraints of imaging in the acute phase of stroke are: the need to be performed as fast as possible to not delay IV thrombolysis (time is brain); machines must be available 24 hours a day, 7 days a week as close as possible to the stroke unit. The aim of imaging are: in routine practice to evaluate the likely benefits (provided by penumbra imaging) and risks of IV thrombolysis; in term of "evidence based medicine" to better evaluate new specific stroke therapies in randomized studies (IV thrombolysis between 3 to 4 hours, use of anti GpIIbIIIa, intra-arterial mechanical or chemical thrombolysis...). Magnetic resonance imaging is considered the goal standard of stroke imaging allowing to evaluate in a "one stop shopping" the level of arterial occlusion, hypoperfusion and brain viability. However, stroke management is a regional issue and performing MR in extreme emergency is almost impossible in all stroke units outside or even within university hospitals 24 hours a day. CT-perfusion and CT angiography are therefore an accurate alternative tool for acute stroke imaging. Multislice CT is indeed available in almost all stroke units. The examination is very time-saving and clinically relevant to make the decision for IV thrombolysis.

Neural substrate for the effects of passive training on sensorimotor cortical representation: a study with functional magnetic resonance imaging in healthy subjects.

Repetitive passive movements are part of most rehabilitation procedures, especially in patients with stroke and motor deficit. However, little is known about the consequences of repeated proprioceptive stimulations on the intracerebral sensorimotor network in humans. Twelve healthy subjects were enrolled, and all underwent two functional magnetic resonance imaging (fMRI) sessions separated by a 1-month interval. Passive daily movement training was performed in six subjects during the time between the two fMRI sessions. The other six subjects had no training and were considered as the control group. The task used during fMRI was calibrated repetitive passive flexion-extension of the wrist similar to those performed during training. The control task was rest. The data were analyzed with SPM96 software. Images were realigned, smoothed, and put into Talairach's neuroanatomical space. The time effect from the repetition of the task was assessed in the control group by comparing activation versus rest in the second session with activation versus rest in the first session. This time effect then was used as null hypothesis to assess the training effect alone in our trained group. Passive movements compared with rest showed activation of most of the cortical areas involved in motor control (i.e., contralateral primary sensorimotor cortex, supplementary motor area [SMA], cingulum, Brodmann area 40, ipsilateral cerebellum). Time effect comparison showed a decreased activity of the primary sensorimotor cortex and SMA and an increased activity of ipsilateral cerebellar hemisphere, compatible with a habituation effect. Training brought about an increased activity of contralateral primary sensorimotor cortex and SMA. A redistribution of SMA activity was observed. The authors demonstrated that passive training with repeated proprioceptive stimulation induces a reorganization of sensorimotor representation in healthy subjects. These changes take place in cortical areas involved in motor preparation and motor execution and represent the neural basis of proprioceptive training, which might benefit patients undergoing rehabilitative procedures.

Within-session and between-session reproducibility of cerebral sensorimotor activation: a test--retest effect evidenced with functional magnetic resonance imaging.

The aim of the current study was to assess the reproducibility of functional magnetic resonance imaging (fMRI) brain activation signals in a sensorimotor task in healthy subjects. Because random or systematic changes are likely to happen when movements are repeated over time, the authors searched for time-dependent changes in the fMRI signal intensity and the extent of activation within and between sessions. Reproducibility was studied on a sensorimotor task called "the active task" that includes a motor output and a sensory feedback, and also on a sensory stimulation called "the passive task" that assessed the sensory input alone. The active task consisted of flexion and extension of the right hand. The subjects had performed it several times before fMRI scanning so that it was well learned. The passive task consisted of a calibrated passive flexion and extension of the right wrist. Tasks were 1 Hz-paced. The control state was rest. Subjects naïve to the MRI environment and non--MRI-naïve subjects were studied. Twelve MRI-naïve subjects underwent 3 fMRI sessions separated by 5 hours and 49 days, respectively. During MRI scanning, they performed the active task. Six MRI-naïve subjects underwent 2 fMRI sessions with the passive task 1 month apart. Three non--MRI-naïve subjects performed twice an active 2-Hz self-paced task. The data were analyzed with SPM96 software. For within-session comparison, for active or passive tasks, good reproducibility of fMRI signal activation was found within a session (intra-and interrun reproducibility) whether it was the first, second, or third session. Therefore, no within-session habituation was found with a passive or a well-learned active task. For between-session comparison, for MRI-naïve or non--MRI-naïve subjects, and with the active or the passive task, activation was increased in the contralateral premotor cortex and in ispsilateral anterior cerebellar cortex but was decreased in the primary sensorimotor cortex, parietal cortex, and posterior supplementary motor area at the second session. The lower cortical signal was characterized by reduced activated areas with no change in maximum peak intensity in most cases. Changes were partially reversed at the third session. Part of the test-retest effect may come from habituation of the MRI experiment context. Less attention and stress at the second and third sessions may be components of the inhibition of cortical activity. Because the changes became reversed, the authors suggest that, beyond the habituation process, a learning process occurred that had nothing to do with procedural learning, because the tasks were well learned or passive. A long-term memory representation of the sensorimotor task, not only with its characteristics (for example, amplitude, frequency) but also with its context (fMRI), can become integrated into the motor system along the sessions. Furthermore, the pattern observed in the fMRI signal changes might evoke a consolidation process.

Cortical intraoperative stimulation in brain tumors as a tool to evaluate spatial data from motor functional MRI.

RATIONALE AND OBJECTIVE: The purpose of this prospective, double-blind study was to correlate motor functional MRI (fMRI) with cortical brain mapping by intraoperative stimulation using 3D reconstructed images of the surface of the brain, and to validate the spatial data of fMRI in patients with brain tumors. METHODS: Fourteen patients with tumors of the rolandic region underwent functional MR mapping of the hand region and subsequently cortical mapping before tumor resection. Data obtained with fMRI and brain mapping were not known previously by the neurosurgeon and by the neuroradiologist, respectively (double-blind study). RESULTS: In each case, the results of direct cortical mapping matched those obtained with fMRI, both positively and negatively, although the extent of the functional activations was larger than the area required to elicit the corresponding movement during intraoperative brain mapping. CONCLUSION: fMRI can be used before surgery to assess motor functional area in patients with rolandic tumors. More studies are needed to validate during surgery the real extent of fMRI activations.

Characterization of choline compounds with in vitro 1H magnetic resonance spectroscopy for the discrimination of primary brain tumors.

RATIONALE AND OBJECTIVES: The authors sought to compare 1H magnetic resonance spectroscopy (MRS) spectra from extracts of low-grade and high-grade gliomas, especially with respect to the signals of choline-containing compounds. METHODS: Perchloric acid extracts of six high-grade and six low-grade gliomas were analyzed by 1H MRS at 9.4 Tesla. RESULTS: The signals of glycerophosphocholine (GPC) at 3.23 ppm, phosphocholine (PC) at 3.22 ppm, and choline (Cho) at 3.21 ppm were identified in both types of tumors. The absolute concentrations of all Cho-containing compounds (GPC + PC + Cho) in high-grade and low-grade gliomas were significantly different. The relative contributions of each of the Cho-containing compounds to the total choline signal were also statistically different. For high-grade gliomas, the choline signal is composed of GPC, PC, and Cho in a well-balanced contribution, whereas in low-grade gliomas, the signal is largely due to GPC with a small involvement of PC and Cho. CONCLUSIONS: The differences in the concentration and the repartition of Cho-containing compounds seem to be a marker of high-grade gliomas. They could also help to discriminate between high- and low-grade gliomas in some difficult cases, especially if there is histologic uncertainty between anaplastic astrocytomas and low-grade oligodendrogliomas.

Preoperative embolization of intracranial meningiomas.

The goal of preoperative embolization of intracranial meningiomas is to facilitate their surgical removal by reducing tumor vascularity and decreasing blood loss during surgery. This study is based on personal experience with about 100 embolized meningiomas and on the experience of others. Embolization is performed during the same session as diagnostic angiography. The appropriate embolic materials (absorbable or nonabsorbable) are chosen according to the location of the tumor, the size of the feeding arteries, the blood flow, and the presence of any potentially dangerous vessels (dangerous anastomoses between external carotid artery and internal carotid or vertebral arteries, arteries supplying the cranial nerves). Preoperative embolization appeared to be very useful in large tumors with pure or predominant external carotid artery supply (convexity meningiomas), in skull-base meningiomas, and in middle fossa and paracavernous meningiomas. It was also useful in falx and parasagittal meningiomas receiving blood supply from the opposite side and in posterior fossa meningiomas. CT low densities demonstrated after embolization did not always correlate with necrosis on microscopic examination, and large areas of infarction could be found despite normal CT. Embolic material was found on pathologic examination in 10%-30% of cases; fresh or recent ischemic and/or hemorrhagic necrosis consistent with technically successful embolization was demonstrated in 40%-60% of cases. With careful technique complications are rare.

Control and placement of intracranial microcatheters.

Balloon-tipped microcatheters allow flow-guided entry into small vessels and permit selective angiography, selective drug infusion, temporary or permanent vessel occlusion, and controlled deposition of tissue adhesives. However, active directive techniques are not usually successful with balloon microcatheters, and more passive flow-directed maneuvering must be learned. Three conditions may be encountered. In the first, the vessel to be entered is large and exits at a small angle from the parent vessel. Flow and momentum carry the microcatheter toward the goal. In the second, the abnormal vessel exists at a large angle but is larger than the continuing vessel. Inflating the balloon until it is larger than the continuing vessel will cause the flow to carry it around even sharp bends. In the third, the abnormal vessel is small and also exits at a large angle. Two balloons must then be used. The first occludes the larger mainline continuing vessel, while a second is injected; flow then carries the second around the bend.

Investigation of extracranial cerebral arteries by intravenous angiography: report of 1,000 cases.

Intravenous angiography is a a safe, rapid, simple examination, which, with sonography, is complementary in selecting patients for conventional angiography. This examination is not designed to replace conventional angiography, but, rather, to study high-risk stroke patients, patients with asymptomatic cervical bruit, or postoperative patients. Improvements in contrast media, film subtraction, the use of oral anesthesia with viscous lidocaine, and the technique of cooling the contrast medium have made the procedure more successful. A review of 1,000 examinations was undertaken to determine the accuracy of the technique and to emphasize technical points. Excellent results, comparable to conventional angiography, were obtained in 50.3% patients and good results in 32%. Poor or uninterpretable results were obtained in 17.7%. These were secondary to either patient movement or the presence of venous reflux or statis of contrast medium.

Internal capsule: normal anatomy and ischemic changes demonstrated by computed tomography.

The purpose of this study was two-fold: (1) to attempt to localize the different parts of the internal capsule on computed tomography (CT) axial sections and (2) to correlate clinical data and CT appearance of 25 cases of ischemic capsular lesions. Twenty-three of the ischemic lesions produced a pure motor hemiplegia. The internal capsule was studied on routine CT axial sections parallel to the canthomeatal line with 8 mm collimation before and after intravenous contrast medium injection. Absorption values of the white matter at the level of the anterior limb of the internal capsule were found to be a little higher (mean, 32 Hounsfield units [H]) when compared with the posterior limb (mean, 28 H). Lesions were classified according to the topography of the internal capsule: anterior limb (three), genu (one), posterior limb (seven), and putaminocapsulocaudate (14). CT appears to be the most sensitive and reliable method to investigate small deep cerebral infarcts since isotope scans were positive in only two of 13 cases, while angiography was positive in eight of 17 cases.

Clinical-MRI correlations in the secondary progressive phase of MS: lessons from the treatment trials.

Conventional MRI techniques are sensitive to detect MS lesions and their change overtime. In relapsing-remitting MS correlations with clinical measures are weak suggesting a pathological heterogeneity of these lesions. There are less data available in secondary progressive phase of the disease. The best source for clinical MRI correlations analysis is the placebo arm of the published interferon beta trials. This review presents the main clinical-MRI findings from these trials then focuses on recent promising observations obtained with non conventional MRI techniques in SP MS patients.

Lumbar phlebography in the diagnosis of disc herniations.

The authors report their experience with 240 cases with lumbar phlebography in the diagnosis of lumbar disc herniations. The normal radiological anatomy and the radiological signs of disc herniations are described. Indications for phlebography are given, and the reliability of this test is compared with that of myelography performed with water-soluble agents.

Mucoceles of the paranasal sinuses: uncommon location.

Mucoceles are the most common lesions causing expansion of the paranasal sinuses. The sinuses most commonly involved are, in decreasing order of frequency, frontal sinus, ethmoid sinuses, maxillary sinus and sphenoid sinus. We reviewed 46 cases of surgically proven mucoceles and the purpose of this study was to report five cases of mucoceles in an uncommon location.

[Results of magnetic resonance imaging in the acute phase of cerebral infarction]. / Résultats de l'imagerie par résonance magnétique a la phase aiguë de l'infarctus cérébral.

Brain ischemia is now possible to trace through the multiple facets of MRI, morphological as well as functional. Experimental studies have been conducted for many years and clinical feasibility is reached. Although the initial decrease in blood flow does not influence morphological imaging, this early phase is shown with functional MRI, either with diffusion imaging or with cerebral blood volume imaging. The later is achieved either with the calculation of the integral of the first passage of a bolus of a diffusible paramagnetic agent or with the circulation of positive or negative blood pool contrast agents. This may serve to confirm an early diagnosis before inclusion in therapeutic trials. Immediate metabolic changes are reflected on phosphorus and proton spectroscopy achievable during the same session as imaging. This type of information may at this stage serve as a reference. It allows observation of the turnover of lactate over time in the lesion and the neuronal loss shown by decreased N-acetyl-aspartate. Edema, as a reaction to ischemia, builds up over time and has already been described for long as it modifies T1- and T2- weighted sequences. Similarly the breakdown of the blood-brain barrier is well known on conventional sequences because it produces contrast enhancement.

Magnetic resonance imaging evaluation of lower limb muscles during bed rest--a microgravity simulation model.

Head-down (-6 degrees) bed rest, a microgravity simulation model in humans, leads to muscular atrophy of the lower limbs. Magnetic Resonance Imaging (MRI) at 0.5 tesla was performed at 1 year intervals on the same six volunteers (except one) before and after 1 month bed rest. Three of the six subjects were daily exposed in a lying position to LBNP (lower body negative pressure), a countermeasure to cardiovascular deconditioning (LBNP group). The groups were exchanged the second year. After bed rest, the quadriceps of the thigh lost uniformly 11% of its cross section area (CSA) and the triceps of the leg 10.5%, with 12.8% lost from the deeper soleus versus 8.5% from the gastrocnemius (p < 0.05). LBNP produced no effect on these changes. The MRI signal intensity of muscles exhibited a trend toward higher values after bed rest although without statistical significance. MRI allowing for noninvasive and reliable quantification of muscle fibers of the lower limbs is an excellent procedure for the assessment of muscle disuse and countermeasures.

[Computerized cisternography with metrizamide]. / Cisternographie computérisée au métrizamide.

Metrizamide, a new water-soluble contrast medium with low toxicity, was used for cranial computed tomography (computerized cisternography) in 26 patients. When injected by lumbar puncture, the pericerebral cisterns (posterior fossa and sella turcica especially), can be visualized with much greater precision than with classical computed tomography. It also allows the normal and pathological circulation of the CSF to be studied. The authors report on 6 cases of tumours of the posterior fossa, 10 cases of pituitary tumours, 2 cases of "empty" sella, 2 cases of CSF rhinorrhoea, 2 cases of normal pressure hydrocephalus, and 2 cases of syringomyelia, studied by this method. The examination was normal in 3 cases. The authors stress the rapidity, reliability, and good tolerance of this new method.

[New MRI techniques in multiple sclerosis]. / Nouvelles techniques IRM et SEP: IRM de diffusion, spectroscopie et transfert d'aimantation.

Early imaging investigations in multiple sclerosis (MS) described focal signs. Technological progress now suggests this concept should be revisited as more diffuse anomalies of the central nervous system are described, sometimes involving regions that appear normal with conventional imaging techniques. This integrative concept results largely from the contribution of magnetic resonance imaging techniques recently broadened to in vivo investigations. Technical developments in MRI now provide new contrast images (magnetization transfer, diffusion, anisotropic diffusion, functional MRI using the BOLD method) as well as new variants of conventional sequences designed to demonstrate specific aspects of the MS lesions: FLAIR sequence (a T2-weighted sequence), black holes (a particular aspect on T1-weighted images), cord atrophy (quantification of the axial section of the cord on T1-weighted sequences). Together these new methods should improve diagnostic sensitivity (FLAIR) or provide prognosis information not provided by conventional sequences (T2 or T2 weighted images with or without gadolinium injection).

[MRI visualization of multiple sclerosis lesions]. / Visualisation I.R.M. des lésions de S.E.P.

Magnetic resonance imaging represents voxels (volume elements) of the body placed in a magnet, by their magnetization determined under various acquisition conditions weighting the contrast of the image by the density of free water protons and their relaxation times T1 and T2. Thus, the sensitivity in depicting lesions is high but pathological specificity is poor. Efforts are made to increase the diagnosis powerfulness of M.R.I. in multiple sclerosis: a careful correlation with the clinical presentation and the use of better M.R.I. criteria increase the specificity of the conventional T2 sequences. New sequences such as fast spin echo (F.S.E.), turbo spin echo (T.S.E.) or derived from inversion recovery (F.L.A.I.R.: fluid attenuated inversion recovery) improve the detection of lesions. Under specific conditions M.R.I. can be used to monitor the evolution of M.S. Acute phase monitoring focuses on changes in disease activity, new, recurring, enlarging, gadolinium (Gd) enhancing lesions, and chronic phase monitoring appreciate the burden of the disease. However M.R.I. is always considered as a secondary outcome in the phase III trials because insufficient correlations with the clinical disability. In the neurological daily practice conventional M.R.I. is of poor interest in the follow up of individual M.S. patients considering the weakness of prognosis value and the problems in the measurement of the lesions load which is emphasized in the methodology of the clinical trials. Nevertheless, there is a continuing search for techniques which correlate better with clinical measures of the disease such as the quantification of "black holes" on T1 w images or the cerebral and spinal atrophy. New techniques allow to weight the signal by the movement (diffusion imaging), by the complexity of the molecular architecture (magnetization transfer imaging), by the chemical shift (chemical shift imaging) or by the local status of oxygenation (functional M.R.I.). The basic aspects of the pathological lesions in M.S., edema, membrane disruption, demyelination, gliosis, cellular infiltration and axonal loss can be studied more precisely by these new M.R. techniques which should better describe the actual clinical impact of the destructive process. In the last year the importance of axonal loss has simultaneously been confirmed by M. R. spectroscopy and pathological findings. However, magnetization transfer imaging, M.R. diffusion imaging and functional M.R.I. are intensively under investigation for a better analysis of these different factors conditioning the reversibility of the patient disability.