Showing papers by "Thomas Nägele published in 2004"

Diffusion-weighted MRI of spinal cord infarction--high resolution imaging and time course of diffusion abnormality.

Abstract: Infarction is a rare cause of spinal cord dysfunction. Whereas diffusion-weighted (DW) MRI has been established as a highly sensitive technique for assessing acute cerebral ischemia, its role in spinal cord infarction remains to be determined. The purpose of this study is to present the signal characteristics of acute spinal cord ischemia using DWMRI within the first two days and after one week. MRI including DW imaging (DWI) was performed in three patients with acute spinal cord dysfunction 8, 12 and 30 hours after the onset of symptoms and repeated after one week in two patients. Two initial scans included EPI DW sequences in transverse and sagittal orientation. The remaining examinations were performed with an optimised high-spatial resolution DWI sequence in the transverse plane. The diagnosis of spinal cord ischemia was established by imaging, clinical history and CSF analysis. T2 signal abnormality and restricted diffusion was demonstrated in all initial examinations. Transverse DW sequences had the highest sensitivity. The spinal infarctions were mainly located in the centre of the spinal cord and the grey matter. Contrast enhancement was absent. After one week, the restricted diffusion had normalised (pseudo normalisation) whereas the T2 signal changes had become more prominent. Restricted diffusion in the course of spinal cord ischemic infarction can be demonstrated using DW-MRI. Whereas a diffusion abnormality can be found after few hours, it does not last for longer than one week. At this time, the establishment of the diagnosis has to rely mainly on T2-weighted images with additional post contrast T1-weighted images being useful.

Diffusion-weighted MRI in herpes simplex encephalitis: a report of three cases

Abstract: Herpes simplex virus encephalitis (HSVE) is the most frequent fatal viral infection of the brain. Because antiviral treatment may improve the prognosis significantly, early diagnosis is mandatory. Imaging diagnosis rests on conventional MRI for the visualization of lesions in the limbic system, the hallmark of HSVE. Diffusion-weighted MRI (DW-MRI) has not been used for the evaluation of HSVE. We report on the DW-MRI findings in three patients with HSVE, who had cortical diffusion abnormalities in affected brain parenchyma, partially as the initial or most sensitive sign of encephalitis. Sequential imaging showed that the diffusion abnormality started to return to normal after 2 weeks in the presence of persistent contrast uptake. Thus, DW-MRI may be a valuable tool for early detection and diagnosis of HSVE whereas contrast-enhanced images are indispensable after the first week.

Retroclival ecchordosis physaliphora: MR imaging and review of the literature

Abstract: BACKGROUND AND PURPOSE: Ecchordosis physaliphora (EP), found in about 2% of autopsies, is a clinically inconspicuous notochordal remnant appearing at the dorsal wall of the clivus. To our knowledge, a systematic review of its MR features does not exist. The aim of this study was to describe the MR imaging findings of incidentally found retroclival EP with special respect to its differentiation from intradural chordomas. METHODS: We reviewed 300 consecutive 1.5-T MR imaging studies that included thin-section transverse T2-weighted images of the skull base for the presence of a retroclival EP. In cases in which an EP was identified, two neuroradiologists observed MR signal intensity characteristics, contrast enhancement, size, form, stalk of EP, and signal intensity changes of the adjacent clivus. RESULTS: Five cases with retroclival EP were found (incidence, 1.7%). In all cases, the ecchordoses was hyperintense on T2-weighted images and hypointense on T1-weighted images. Contrary to the reported findings in chordomas, none of the lesions showed contrast enhancement. In four cases, there were signal intensity changes in the adjacent clivus. A stalklike connection between clivus and EP was seen in three patients. CONCLUSION: Because of the benign character of EP and the difficulties in its histopathologic differentiation from chordomas, precise knowledge of the radiologic characteristics of EP is important. On the basis of these five cases and a review of literature, contrast enhancement and the presence of clinical symptoms seem to be highly reliable parameters in the differential diagnosis of intradural chordoma and EP.

Modern MRI tools for the characterization of acute demyelinating lesions: value of chemical shift and diffusion-weighted imaging.

Abstract: Acute demyelinating lesions occur in various inflammatory disorders of the CNS. Apart from multiple sclerosis, most cases can be attributed to an overshooting immunological response to infectious agents called acute disseminated encephalomyelitis (ADEM). ADEM, which is mostly characterized by a monophasic course, has a multiphasic variant (MDEM). The early application of corticosteroids has been shown to be beneficial for the outcome; thus, an early diagnosis is highly desirable. Furthermore, the differential diagnosis ruling out neoplastic disorders may be difficult using conventional MRI alone. The potential diagnostic value of advanced MR techniques such as chemical shift imaging (CSI) and diffusion-weighted imaging (DWI) was investigated in a patient with MDEM, who had a new lesion in continuity with the initial disease manifestation. CSI was performed at 1.5 T with a long echo time of 135 ms for the evaluation of N-acetyl-aspartate (NAA) and choline (Cho) and with short TE of 30 ms for macromolecules (mm) and myo-Inositol (mI). DWI was performed using a single-shot isotropic EPI sequence. Whereas acute and chronic areas of demyelination were neither distinguishable on T2- nor on contrast-enhanced T1-weighted images, CSI and DWI revealed different metabolite concentrations and diffusion characteristics within the composite lesion, clearly separating acute from chronic areas of demyelination. In conclusion, the addition of CSI and DWI may add to the diagnostic power of MRI in the setting of demyelinating disorders by identifying areas of acute and chronic demyelination, even in the absence of contrast enhancement.

Molecular imaging: Bridging the gap between neuroradiology and neurohistology.

Abstract: Historically, in vivo imaging methods have largely relied on imaging gross anatomy. More recently it has become possible to depict biological processes at the cellular and molecular level. These new research methods use magnetic resonance imaging (MRI), positron emission tomography (PET), near-infrared optical imaging, scintigraphy, and autoradiography in vivo and in vitro. Of primary interest is the development of methods using MRI and PET with which the progress of gene therapy in glioblastoma (herpes simplex virus–thymidine kinase) and Parkinson’s disease can be monitored and graphically displayed. The distribution of serotonin receptors in the human brain and the duration of serotonin- receptor antagonist binding can be assessed by PET. With PET, it is possible to localize neurofibrillary tangles (NFTs) and s-amyloid senile plaques (APs) in the brains of living Alzheimer disease (AD) patients. MR tracking of transplanted oligodendrocyte progenitors is feasible for determining the extent of remyelinization in myelin-deficient rats. Stroke therapy in adult rats with subventricular zone cells can be monitored by MRI. Transgene expression (s-galactosidase, tyrosinase, engineered transferrin receptor) can also be visualized using MRI. Macrophages can be marked with certain iron-containing contrast agents which, through accumulation at the margins of glioblastomas, ameliorate the visual demarcation in MRI. The use of near-infrared optical imaging techniques to visualize matrix-metalloproteinases and cathepsin B can improve the assessment of tumor aggressiveness and angiogenesis-inhibitory therapy. Apoptosis could be detected using near-infrared optical imaging representation of caspase 3 activity and annexin B. This review demonstrates the need for neurohistological research if further progress is to be made in the emerging but burgeoning field of molecular imaging.

MRI for the management of neonatal cerebral infarctions: importance of timing.

Abstract: Purpose Focal ischemic stroke in neonates is a rare occurrence. Diagnosis with most imaging modalities is difficult, but necessary for initiating an anticoagulatory treatment. The purpose of this study was to evaluate the sensitivity of MRI sequences within the first 14 days of birth.

3-hydroxy-3-methylglutaryl-CoA lyase deficiency in an adult with leukoencephalopathy.

Abstract: 3-Hydroxy-3-methylglutaryl-CoA lyase deficiency is a disorder of leucine metabolism that usually presents with recurrent episodes of life-threatening hypoglycemia during early childhood. We report on a 36-year-old woman with seizures, recurrent metabolic disturbances, and severe leukoencephalopathy. The diagnosis was made by analysis of amino acids in urine and serum and was confirmed by demonstration of the deficient enzyme in cultured skin fibroblasts. The patient improved clinically on oral L-carnitine substitution. This treatable condition can remain unrecognized in adults and should be considered a potential cause of leukoencephalopathy.

Bilateral Wallerian degeneration of the middle cerebellar peduncles due to paramedian pontine infarction: MRI findings.

Abstract: Wallerian degeneration is a frequent finding in lesions of the pyramidal tract, but has been observed after damage of the other fibre systems as well. Few reports exist about Wallerian degeneration of cerebellar fibres after distant lesions to the axons. Here, we report on a patient who developed degeneration of both middle cerebellar peduncles after a paramedian pontine infarction.

Transient crossed aphasia during focal right-hemisphere seizure.

Abstract: In nearly all right- and left-handed individuals, language is bound to the left hemisphere. Acquired language disorders subse- quent to right-hemisphere brain lesions in right-handed subjects amount to 1 to 3% of aphasic syndromes only.1 We report the rare case of a 59-year-old right-handed woman with transient global aphasia as the sole manifestation of …

Experimental autoimmune encephalomyelitis (EAE): lesion visualization on a 3 Tesla clinical whole-body system after intraperitoneal contrast injection.

Abstract: Purpose To investigate the intravital visibility of CNS lesions in rats with experimental autoimmune encephalomyelitis (EAE), the animal correlate of multiple sclerosis, using a 3-Tesla (T) whole-body MR system. Materials and methods Three healthy Dark Agouti (DA) rats and 16 DA rats with clinical signs of EAE were examined on a 3T whole body-system using a normal wrist coil. In total, 25 examinations were preformed using T2- and T1-weigthed images in transverse and sagittal orientation with a slice thickness of 2 mm or 1 mm (voxel size up to 0.2 x 0.2 x 1 mm). Sedation was achieved by intraperitoneal injection of ketamine and xylazine. In addition, T1-weighted images were obtained after the instillation of 1.0 ml of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) (0.5 mmol/ml) into the peritoneal cavity. Results T2- and T1-weighted images of the brain and spinal cord with high spatial and contrast resolution could be obtained in all animals. The anatomical details of the olfactory bulb glomeruli, cerebellum foliae, ventricles and corpus callosum were clearly visible. The EAE lesions presented as hyperintense areas in T2-weighted images and could be demonstrated in all clinically affected animals by MRI and histologically verified. In total, the 16 affected rats had 28 cerebral and 2 spinal cord lesions (range 1 to 4, median 2). Contrast enhancement was noted in 12 animals and ranked as severe in ten and moderate in two cases. No adverse effects were noted due to sedation or intraperitoneal contrast injection. Conclusions The intravital demonstration of cerebral and spinal cord EAE lesions in rats is possible on a 3T whole-body MR scanner using a normal wrist coil. Intraperitoneal injection of ketamine/xylazine and contrast agent is an easy, safe and effective procedure in rats.

Isolated ischemic internuclear ophthalmoplegia: toward the resolution limits of DW-MRI

Abstract: Sirs, Internuclear ophthalmoplegia (INO) is a frequent brainstem syndrome due to a lesion of the longitudinal medial fascicle (MLF). Most cases were attributed to multiple sclerosis 3 . Because of vascular anatomy and the close proximity to other eloquent midbrain structures, an ischemic pathogenesis of an isolated INO is thought to be extremely rare. We report on two patients with isolated INO, in whom the ischemic origin could be established by MRI.

Berechnung von Protonenspektren reiner Gewebeanteile im Gehirn mittels Mehrfach-Voxelmessungen und Bildsegmentierung

Abstract: Zusammenfassung In der lokalisierten In-vivo-Protonen-NMR-Spektroskopie (1H-MRS) des menschlichen Gehirns lasst es sich oft nicht vermeiden, dass im ausgewahlten Messvolumen (Voxel) sowohl graue Substanz (GM) als auch weise Substanz (WM) enthalten ist. Da sich die Spektren von GM und WM im Allgemeinen unterscheiden, stellt das akquirierte Spektrum ein Mischspektrum dar, das von der Gewebezusammensetzung im Voxel abhangt. In dieser Studie wird eine Methode vorgestellt, mit der Spektren der reinen Gewebearten GM und WM aus Mischspektren bestimmt werden konnen. Die Reingewebespektren werden dabei aus gemessenen Spektren berechnet, die aus mehreren Voxeln mit unterschiedlicher Gewebezusammensetzung aufgenommen wurden. Hierzu muss die Gewebezusammensetzung in den Voxeln bekannt sein. Sie wird durch Segmentierung zusatzlich aufgenommener 3D-NMR-Bilddatensatze mit hoherer Ortsauflosung ermittelt. In Probandenuntersuchungen wurden Messungen in verschiedenen Regionen des Groshirns sowie im Kleinhirn und im Thalamus durchgefuhrt. In allen untersuchten Hirnregionen zeigten sich deutliche Unterschiede zwischen den Reingewebespektren von WM und GM, wobei der Unterschied im Kleinhirn besonders stark ausgepragt war. Die gefundenen Unterschiede in den Spektren von WM und GM indizieren, dass bei Patientenstudien auf die Gewebezusammensetzung im Voxel geachtet werden muss, um krankheitsbedingte Veranderungen in den Spektren von Effekten unterschiedlicher Gewebezusammensetzungen unterscheiden zu konnen.

Zerebrale Infarkte bei Neugeborenen: Wertigkeit der MRT

Abstract: Zerebrale Ischamien bei Neugeborenen sind selten. Wegen der Unreife des Gehirns sind Krampfanfalle fast immer das klinische Leitsymptom. Der hohe Wassergehalt des neonatalen Gehirns und die fehlende Myelinisierung erschweren die Diagnose mit bildgebenden Verfahren, die zur Indikationsstellung einer antikoagulatorischen Therapie jedoch erforderlich ist. Zweck dieser Studie war die Evaluation verschiedener Magnetresonanztomographie-(MRT-)Sequenzen zur Erkennung zerebraler Ischamien wahrend der ersten 14 Lebenstage unter besonderer Berucksichtigung der diffusionsgewichteten Bildgebung. Sechs Patienten mit zerebralen Krampfanfallen wurden in den ersten 2 Lebenstagen nach einem festgelegten MRT-Protokoll untersucht, das neben konventionellen Sequenzen jeweils auch diffusions- und flussgewichtete Aufnahmen enthielt. Verlaufsuntersuchungen wurden bei vier Patienten nach 5 Tagen (n = 1), 7 Tagen (n = 2) und 14 Tagen (n = 1) durchgefuhrt. Insgesamt wurden bei den sechs Patienten 19 Infarkte festgestellt. Die Infarkte waren in der Initialphase als starke Diffusionsstorung erkennbar. Die Erkennbarkeit in den T2-gewichteten Sequenzen war bei drei Patienten initial so gering, dass die Diagnose durch die diffusionsgewichteten Sequenzen erst moglich wurde. Bei den anderen Patienten waren in der Diffusionsbildgebung deutlich mehr Lasionen (19) erkennbar als in den konventionellen Sequenzen (6). Im zeitlichen Verlauf waren die Infarkte in der Diffusionsbildgebung nach 5 Tagen bereits deutlich schlechter sichtbar und nach 1 Woche nicht mehr abgrenzbar. Eine verstarkte Diffusivitat in den Infarktarealen bestand bereits 2 Wochen nach der Ischamie. Die Ischamien waren zu diesem Zeitpunkt in den T2-Sequenzen gut erkennbar. Diffusionsgewichtete Sequenzen sind bei Neugeborenen am besten geeignet, zerebrale Ischamien in der Initialphase nachzuweisen. Weil ihre Sensitivitat aber schon in der ersten Woche nachlasst, muss sich die Diagnose nach dem 5. Tag auf T2-gewichtete Sequenzen stutzen.