Adult and neonatal human brain: diffusional anisotropy and myelination with diffusion-weighted MR imaging

Diffusional anisotropy of human brain was investigated clinically in six adult volunteers, eight premature neonates, and three infants aged 5-10 months. Diffusion-weighted magnetic resonance imaging was performed with gradient b of 450 sec/mm2. The direction of diffusion-sensitive gradients was changed among x, y, and z axes according to the orientation of neurofibers in white matter. T1- and T2-weighted images also were obtained for evaluation of myelination. Diffusional anisotropy was demonstrated in white matter in the adults. Extensive signal attenuation was observed when gradients were parallel to white matter fibers. Conversely, in neonates, diffusional anisotropy of white matter, in which no myelination was shown on T1- and T2-weighted images, was weak. Diffusional anisotropy was more distinct after brain maturation, as observed in adult white matter. Detection of diffusional anisotropy is useful in evaluating neonatal brain development and various white matter disorders.     

Normal myelination of the pediatric brain imaged with fluid-attenuated inversion-recovery (FLAIR) MR imaging.

BACKGROUND AND PURPOSE: As in adult imaging, FLAIR can be applied to pediatric brain imaging, and this requires an appreciation of the normal pediatric brain appearance by FLAIR imaging. The purpose of this study was to describe the MR appearance of the brain in normal infants and young children as demonstrated by fluid-attenuated inversion-recovery (FLAIR) MR imaging. METHODS: We retrospectively examined MR brain studies, interpreted as normal by pediatric radiologists, from 29 patients (aged 1 to 42 months) to catalog the appearance of myelination in multiple brain areas. RESULTS: On T2-weighted images, white matter progressed from hyperintense to hypointense relative to adjacent gray matter over the first 2 years of life. An analogous, although slightly delayed sequence was observed on FLAIR images with the exception of the deep cerebral hemispheric white matter, which followed a triphasic sequence of development. On FLAIR images, the deep cerebral white matter was heterogeneously hypointense relative to gray matter in the young infant, became hyperintense early in the first few months of life, and then reverted to hypointense during the second year of life. CONCLUSION: The normal appearance and development of brain white matter must be taken into account when interpreting FLAIR images of infants and young children.     

Accelerated myelination in early Sturge-Weber syndrome demonstrated by MR imaging

Magnetic resonance imaging of the brain in two infants with Sturge-Weber syndrome has demonstrated a pattern of accelerated myelination in the abnormal cerebral hemisphere. The extent of myelination was most apparent on the T1-weighted inversion recovery sequence while the T2-weighted images demonstrated concomitant changes in hydration of the brain. We propose an explanation for this finding based on cerebral ischemia underlying the leptomeningeal angioma.     

Ultra-fast three-dimensional MR perfusion imaging of the entire brain in acute stroke assessment

We sought to evaluate a three-dimensional (3D) whole-brain perfusion technique based on echo-shifting (PRESTO) for its performance in evaluation of acute stroke. Twenty-six patients were scanned within 6 hours after onset of hemispheric symptoms, and the results were compared with results of diffusion-weighted imaging (DWI) and digital subtraction angiography (DSA). The signal-to-noise ratio of the images was 61 +/- 3 pre-contrast and 47 +/- 3 at the bolus peak. Brain coverage on perfusion parameter maps was 95% +/- 2% compared with that displayed on T2-weighted images, with only minor artifacts related to susceptibility at the skull base. Measured regional cerebral blood volume (rCBV) reduction closely correlated to lesion size on initial DWI and to final clinical outcome (P = 0.006), consistent with results previously reported for 2D perfusion methods. Mismatches between DWI and perfusion imaging characterized the total extent of tissue at risk, and the contrast timing correlated with the amount of collateral circulation as shown on DSA. In conclusion, 3D imaging using the PRESTO technique permits high-quality perfusion imaging of the entire brain.     

Cytotoxic brain edema: assessment with diffusion-weighted MR imaging.

To determine whether cytotoxic brain edema is associated with a decrease in diffusion, it was induced in rats, in the absence of ischemia, with an established model of acute hyponatremic encephalopathy. Cytotoxic brain edema secondary to acute hyponatremia was induced with intraperitoneal injections of 2.5% dextrose in water and subcutaneous injection of arginine-vasopressin. Coronal spin-echo magnetic resonance (MR) images were obtained with and without strong diffusion-sensitizing gradients before and after induction of acute hyponatremia. The apparent diffusion coefficient (ADC) was measured at two coronal section locations. In hyponatremic rats, the brain ADC was significantly reduced (P = .0153 and .0001) and was positively correlated with increased total brain water content (P = .0011). Plots of ADC versus total brain water showed a statistically significant inverse linear relationship between ADC and increasing brain water at the anterior coronal section location. The results indicate that the ADC may be a sensitive indicator of cytotoxic brain edema and thus may enable quantitative evaluation of such edema with diffusion-weighted MR imaging.     

Relationship between MR imaging and histopathologic findings of the brain in extremely sick preterm infants.

BACKGROUND AND PURPOSE: MR imaging can now be used safely in extremely preterm infants. The aim of this study was to compare the MR imaging appearance of the immature brain with neuropathologic findings at postmortem examination. METHODS: Seven extremely sick preterm infants, born at a median of 24 weeks' gestation, were studied using T1- and T2-weighted MR sequences. Infants died at a median of 3 days after initial MR imaging, and postmortem examinations were carried out. RESULTS: The cortex and germinal matrix were seen as areas of low signal intensity on T2-weighted images, which corresponded to their highly cellular histologic appearance. The periventricular and subcortical layers of white matter had a high signal intensity, corresponding to high fiber and relatively low cellular density; the intermediate layer of low signal intensity corresponded to a dense band of migrating cells. Regions of acute hemorrhage were seen as low signal intensity and regions of infarction as high signal intensity on T2-weighted images. One infant with mild periventricular leukomalacia had some low signal intensity on T1-weighted images, but no focal changes on T2-weighted images. Regions of neuronal mineralization, seen in association with infarction and capillary proliferation, within the basal ganglia and thalami were characterized by very low signal intensity on T2-weighted images and by very high signal intensity on T1-weighted images. There were no imaging abnormalities detected in regions with more subtle histologic abnormalities, such as increased glial or apoptotic cells. CONCLUSION: MR imaging can be used to observe normal developing brain anatomy in extremely premature infants; it can detect areas of hemorrhage and infarction within the developing brain, but conventional MR imaging may not detect more subtle histologic abnormalities.     

Diffusion-weighted MR imaging of the brain

Diffusion-weighted magnetic resonance (MR) imaging provides image contrast that is different from that provided by conventional MR techniques. It is particularly sensitive for detection of acute ischemic stroke and differentiation of acute stroke from other processes that manifest with sudden neurologic deficits. Diffusion-weighted MR imaging also provides adjunctive information for other cerebral diseases including neoplasms, intracranial infections, traumatic brain injury, and demyelinating processes. Because stroke is common and in the differential diagnosis of most acute neurologic events, diffusion-weighted MR imaging should be considered an essential sequence, and its use in most brain MR studies is recommended.     

早产儿白质MR影像表现的临床意义:一项2年的随访研究

目的在等价年龄段(TEA)研究弥漫超高信号强度(DEHSI)、斑点状白质(WM)病变和脑室扩张之间的联系,并对早产儿临床随访2年,探索其对神经发育的影响。材料与方法机构审查委员会给予此项前瞻性研究伦理支持并获得     

MR imaging assessment of brain and cervical cord damage in patients with neuroborreliosis

BACKGROUND AND PURPOSE: Neuroborreliosis is frequently indistinguishable from multiple sclerosis (MS) on both clinical and radiologic grounds. By using MR imaging, we assessed "occult" brain white matter (WM), brain gray matter (GM), and cervical cord damage in patients with neuroborreliosis in an attempt to achieve a more accurate picture of tissue damage in these patients, which might contribute to the diagnostic work-up. METHODS: We studied 20 patients with neuroborreliosis and 11 sex- and age-matched control subjects. In all subjects, we acquired dual echo, T1-weighted, diffusion tensor (DT) and magnetization transfer (MT) MR imaging scans of the brain and fast short-tau inversion recovery and MT MR imaging scans of the cervical cord. T2-visible lesion load was measured by using a local thresholding segmentation technique. Mean diffusivity and fractional anisotropy histograms of the brain and cervical cord MT ratio histograms were produced. Normalized brain volumes (NBV) were measured by using SIENAx. RESULTS: Brain T2-visible lesions were detected in 12 patients, whereas no occult damage in the normal-appearing WM and GM was disclosed by using MT and DT MR imaging. No macroscopic lesions were found in the cervical cord, which was also spared by occult pathology. NBV did not differ between patients with neuroborreliosis and control subjects. CONCLUSION: This study shows that, contrary to what happens in MS, occult brain tissue damage and cervical cord pathology are not frequent findings in patients with neuroborreliosis. These observations might be useful in the diagnostic work-up of patients with neuroborreliosis and T2 brain lesions undistinguishable from those of MS.     

新生儿和婴幼儿脑髓鞘发育的DTI

目的：探讨平均扩散率（MD）和部分各向异性（FA）在新生儿和婴幼儿脑髓鞘发育过程中的变化规律。方法：将97例围产史正常、无器质性神经系统疾病的足月新生儿和婴幼儿按年龄段分为7组,行颅脑扩散张量成像（DTI）扫描,测量主要白质结构的MD值和FA值,分析其在不同脑区的差异及随年龄变化的规律。结果：脑各部位的MD值随着年龄的增长而减低（P〈0.01）,FA值随年龄的增长而增高（P〈0.01）。脑同一部位的MD值和FA值在不同年龄段的变化速率有所不同,同一年龄段脑不同部位MD值和FA值的变化幅度不尽相同,不同部位的MD值和FA值也存在差异。结论：MD值和FA值相结合,能定量的分析髓鞘化进程,评估脑白质发育情况。     

MR imaging of fetal brain

Magnetic resonance (MR) imaging was used to evaluate normal fetal intracranial anatomy in axial, coronal, and sagittal planes. The T1 and T2 weighted images (WI) of aborted fetuses of varying gestational ages were correlated with anatomic sections. In the premature fetus three distinct intensity zones were seen on MR that were not visualized on gross specimens. Unmyelinated white matter displays low intensity on T1 W1 and high intensity on T2 W1. Maturational changes of the brain were observed with advancing fetal age.     

MR imaging of brain abscesses

The MR images and CT scans of 14 patients with surgically verified pyogenic cerebral abscesses were reviewed. The MR findings correlated well with those seen on CT and were believed to be sufficiently characteristic to allow early and accurate diagnosis with MR alone. These features include (1) peripheral edema producing mild hypointensity on short TR/short TE and marked hyperintensity on long TR/intermediate to long TE scans; (2) central necrosis with abscess fluid hypointense relative to white matter and hyperintense relative to CSF on short TR/short TE scans and hyperintense relative to gray matter on long TR/intermediate to long TE scans (the fluid had concentric zones of varying intensity in seven cases, a finding not previously identified in other lesions); (3) extraparenchymal spread (intraventricular or subarachnoid), which was detected more easily on MR than on CT and was manifested by increased intensity relative to normal CSF on both short TR/short TE and long TR/intermediate TE scans; and (4) visualization of the abscess capsule, which was iso- to mildly hyperintense relative to brain on short TR/short TE scans and iso- to hypointense relative to white matter on long TR/intermediate to long TE scans. On the long TR scans, the relative hypointensity of the rim allowed for visualization of the typical morphologic features of the capsule, which in turn aided in differentiation of abscesses from other lesions (as it does on CT). To investigate the cause of the capsular intensity, pathologic studies of the capsules were reviewed when available (10 cases). Fibrosis was identified in all mature abscess capsules, but the combination of the intensities seen on short TR/short TE and long TR/intermediate to long TE scans as well as the temporal changes in intensity were believed to be incompatible with fibrosis as a cause of the capsular changes. Intensity patterns were suggestive of hemorrhage, but neither acute nor chronic hemorrhage was identified on routine H and E stains, while iron stain revealed scant hemorrhage in only two of the eight patients in whom these stains were used. We believe the capsular intensity (in particular the hypointense rims on long TR scans) may reflect paramagnetic T1, and to a greater extent T2, shortening, possibly due to the presence of heterogeneously distributed free radicals that are products of the respiratory burst produced by actively phagocytosing macrophages in the capsule wall. Distinctive MR features of pyogenic abscesses should afford early and accurate diagnosis.     

Development and aging of brain midline structures: assessment with MR imaging

The development and aging of four brain midline structures--the pituitary gland, pons, cerebellar vermis, and corpus callosum--were studied. The dimensions and area of these structures were measured by means of midsagittal magnetic resonance imaging. The study group consisted of 94 patients newborn to 15 years old and 49 patients and seven volunteers 16-60 years old. Except for growth spurts in the 1st year and in the 10-15-year age range, the pituitary gland showed linear growth. The pons, cerebellar vermis, and corpus callosum all showed exponential growth. The cerebellar vermis showed the sharpest 1st-year growth spurt, followed by the corpus callosum and the pons. The pituitary gland showed a decrease in size in the 51-60-year age range. The corpus callosum also showed a tendency to diminish in size but to a lesser degree. There were no statistically significant declines in the size of either the pons or the cerebellar vermis in the 51-60-year age range.     

MR imaging in congenital disorders of the brain

MR imaging is an excellent tool for use in diagnosing congenital malformations of the brain. Such malformations cannot be reliably recognized or classified without an insight in to the basic processes of the fetal development of the brain. Cortical malformations are classically divided into (1) malformations of neuronal proliferation, i.e. of stem cell proliferation in the periventricular germinal matrix zone, (2) disorders of neuronal migration, i.e. of the radial migration of the neurons from the periventricular germinal matrix zone to the cortical surface, and (3) disorders of cortical organisation. Other cerebral malformations are agenesis or dysgenesis of the corpus callosum, encephaloceles and various kinds of holoprosencephaly. Chiari malformations and disorders on the Dandy-Walker spectrum are relatively common, primarily infratentorial disorders. Rarer infratentorial disorders are Joubert syndrome, rhombencephalosynapsis and Lhermitte Duclos syndrome.