L. Porto

Voxel-based morphometry and diffusion-tensor MR imaging of the brain in long-term survivors of childhood leukemia

The aims of this study were to detect morphological changes in neuroanatomical components in adult survivors of acute lymphoblastic leukemia (ALL). Voxel-based morphometry (VBM) can be used to detect subtle structural changes in brain morphology and via analysis of fractional anisotropy (FA), diffusion-tensor imaging (DTI) can non-invasively probe white matter (WM) integrity. We used VBM and DTI to examine 20 long-term survivors of ALL and 21 healthy matched controls. Ten ALL survivors received chemotherapy and irradiation; ten survivors received chemotherapy alone during childhood. Imaging was performed on a 3.0-T MRI. For VBM, group comparisons of segmented T1-weighted grey matter (GM) and WM images from controls and ALL survivors were performed separately for patients who received chemotherapy alone and who received chemotherapy and irradiation. For DTI, FA in WM was compared for the same groups. Survivors of childhood ALL who underwent cranial irradiation during childhood had smaller WM volumes and reduced GM concentration within the caudate nucleus and thalamus. The FA in WM was reduced in adult survivors of ALL but the effect was more severe after combined treatment with irradiation and chemotherapy. Our results indicate that DTI and VBM can reveal persistent long-term WM and caudate changes in children after ALL treatment, even without T2 changes in conventional imaging.

Agenesis of internal carotid artery associated with congenital anterior hypopituitarism.

Abstract. We report a rare case of unilateral agenesis of the internal carotid artery in association with congenital anterior hypopituitarism. The collateral circulation is supplied by a transsellar intercavernous anastomotic vessel connecting the internal carotid arteries. These abnormalities are well depicted on MRI and MRA. The agenesis of the internal carotid artery may explain the pathogenesis of some of congenital anterior hypopituitarism.

Granulocytic sarcoma in children

We report three children with leukaemia (two acute myeloid and one acute lymphoblastic) and granulocytic sarcoma in the skull, orbit and sinuses. Lesions in these sites in children, with or without bone changes, are suggestive of systemic diseases such as lymphoproliferative conditions. Although involvement by granulocytic sarcoma, with or without acute myeloid leukaemia, is described, an association with acute lymphoblastic leukaemia is rare. Recognition of this rare entity is important, because early aggressive chemotherapy can bring about regression of the tumour and improve survival.

Proton magnetic resonance spectroscopy in childhood brainstem lesions

BackgroundDiagnosis of brainstem lesions in children based on magnetic resonance imaging alone is a challenging problem. Magnetic resonance spectroscopy (MRS) is a noninvasive technique for spatial characterization of biochemical markers in tissues and gives information regarding cell membrane proliferation, neuronal damage, and energy metabolism.MethodsWe measured the concentrations of biochemical markers in five children with brainstem lesions and evaluated their potential diagnostic significance. Images and spectra were acquired on a 1.5-T imager. The concentrations of N-acetylaspartate, tetramethylamines (e.g., choline), creatine, phosphocreatine, lactate, and lipids were measured within lesions located at the brainstem using Point-resolved spectroscopy sequences.ResultsDiagnosis based on localized proton spectroscopy included brainstem glioma, brainstem encephalitis, demyelination, dysmyelination secondary to neurofibromatosis type 1 (NF 1), and possible infection or radiation necrosis. In all but one patient, diagnosis was confirmed by biopsy or by clinical follow-up.ConclusionsThis small sample of patients suggests that MRS is important in the differential diagnosis between proliferative and nonproliferative lesions in patients without neurofibromatosis. Unfortunately, in cases of NF 1, MRS can have a rather misdiagnosis role.

Accelerated myelination associated with venous congestion

Magnetic resonance imaging is currently the gold standard in the assessment of brain myelination. The normal pattern of brain myelination conforms to a fixed chronological sequence. Focal accelerated myelination is a usual pathological state and previously has only been associated with Sturge‐Weber syndrome. The purpose of our study is to describe alternate causes for accelerated myelination. We retrospectively reviewed serial MR scans, MR angiography, conventional angiography and the clinical progress of three children with accelerated myelination. Two patients with accelerated myelination had an underlying cerebral sinovenous thrombosis. The third patient had Sturge‐Weber syndrome. Our study strongly suggests that cerebral venous thrombosis with the consequent restriction of venous outflow could be a key factor in the induction of accelerated myelination. We recommend that in patients with accelerated myelination, the search for an underlying etiology should include careful evaluation of the intracranial vascular pathology, especially cerebral venous thrombosis.

3T in der Neuroradiologie—Spannungsfeld zwischen Wunsch und Wirklichkeit

ZusammenfassungDie Entwicklung der MR-Technologie wird durch zahlreiche Parameter beeinflusst. Insbesondere die Erhöhung der Stärke des statischen Magnetfeldes hat sich in der Vergangenheit als erfolgreiche Methode zur Verbesserung des Signal-zu-Rausch-Verhältnisses (SNR) bewährt. Tatsächlich wurden jedoch mit der Erhöhung der Feldstärke auf 3 Tesla (3T) zahlreiche Probleme u. a. mit der spezifischen Absorptionsrate (SAR), mit ausgeprägten Suszeptibilitätsartefakten insbesondere an der Schädelbasis und stark reduzierten T1-Kontrasten sichtbar. Diese mussten durch zusätzliche Maßnahmen wie den Einsatz der parallelen Bildgebung, neue Sequenzen, aber auch Verfahren zur Verzerrungskorrektur kompensiert werden. Somit induzierte die Erhöhung der Feldstärke auf 3T die Ausbildung einer neuartigen und relativ komplexen Plattform für die MR-Bildgebung. Gewinne für 3T gegenüber 1,5T sind jetzt bereits für die fMRT, die MRA und Perfusionsmessungen mit Spin-Labeling erkennbar. Auch die Signalqualität bei der Spektroskopie wird durch die höhere Feldstärke besser; allerdings müssen unerwartete Einschränkungen bei der Laktatdetektion durch Zusatzmessungen kompensiert werden. Bei der T1-gewichteten Bildgebung der Wirbelsäule besteht noch eindeutig Optimierungsbedarf. Bedingt durch die zunehmende Bedeutung der MR-Bildgebung für die Neurofächer und unterstützt durch die Ausstattung von „Zentren für die Bildgebung in den Neurowissenschaften“ mit 3T-Kernspintomographen, wird eine Justierung der zukünftigen Ziele der Neuroradiologie bei der Entwicklung und Nutzung dieser vielversprechenden Technologie erforderlich.AbstractProgress in MR technology depends on a variety of parameters. Overcoming the inherent poor signal to noise ratio (SNR) by increasing the field strength has been a successful strategy for the past, however, switching from 1.5T to 3T has disclosed several problems including increased specific absorption rate (SAR), striking susceptibility artifacts especially at the base of the scull, and low contrast on T1-weighted images. These drawbacks had to be compensated by additional procedures like parallel imaging, new sequences, and special measures for distortion correction. Consequently, induced by the increase of the field strength to 3T a new and more complex platform for MRI was developed. Benefits of 3T in comparison to 1.5T are already evident regarding fMRI, MRA and perfusion imaging with spin labeling. In addition, there is improved signal quality for spectroscopy at higher field strength, but also an unexpected loss in sensitivity of lactate, which can only be compensated by an additional measurement. At present, T1-weighted images of the spine are unsatisfactory and have to be improved. The increasing importance of MRI in neuroscience will drive further installations of 3T scanners inside of brain imaging centers. In this environment, the role of neuroradiology has to be adjusted as an important player that participates in development and application of this promising new technology.

Cutoff value of choline concentration reliably reveals high-grade brain tumors among other contrast-enhancing brain lesions.

BACKGROUND AND AIM To evaluate whether there is a cutoff value for a metabolite concentration measured by 1 H MR spectroscopy (MRS), which can be used to differentiate malignant brain tumors (high-grade gliomas, primary CNS lymphomas [PCNSL] and metastases) from other contrast-enhancing lesions like low-grade gliomas and non-neoplastic lesions. MATERIAL AND METHODS 1 H MRS was performed in 252 consecutive patients with space-occupying brain lesions which were enhanced with application of a contrast agent. Concentrations of N-acetyl-aspartate, total creatine, choline containing metabolites (total choline, tCho), lipids, and lactate were evaluated from the contrast-enhancing part of the lesions and from the normal appearing brain tissue. Linear discriminant analysis was used to find the best predictor for malignant brain tumors. In addition, receiver operating characteristic analysis (ROC) was performed to determine a cutoff value for the best predictor in detecting malignant brain tumors with a specificity of >95%. RESULTS All brain tumors and 20 out of 47 nonneoplastic lesions were examined histopathologically. The remaining 27 diagnoses were based on MR imaging, clinical findings, and follow-up. The final diagnosis was 134 high-grade gliomas (WHO grade III/IV), 36 metastases, 9 PCNSL, 8 low-grade gliomas (WHO grade I/II), 34 infections, 9 infarctions, 2 hematomas, and 2 vasculitides. 18 patients were excluded due to insufficient spectral quality. The tCho concentration was the best predictor to differentiate malignant brain tumors from enhancing low-grade gliomas or non-neoplastic lesions (F=26.6 [df: 25.833], p<0.0005). The ROC revealed that a cutoff tCho value, based on an increase of ≥40% compared to normal, yielded a specificity of 100% and a sensitivity of 89.4% to correctly diagnose a malignant brain tumor. CONCLUSION 1 H MRS reliably differentiates malignant brain tumors from other contrast-enhancing brain lesions. At least a 40% increase of tCho compared to normal brain tissue indicates a malignant tumor (WHO grade III/IV gliomas, PCNSL, metastases) with >90% specificity and sensitivity.

Migration of an arachnoid cyst of the cisterna quadrigeminalis towards the fourth ventricle.

Journal of Neuroradiology - In Press.Proof corrected by the author Available online since jeudi 21 avril 2011