Diffusion-weighted MRI of middle cerebral artery stroke in a newborn

Perinatal stroke--risk factors and management

Stroke is an uncommon but increasingly recognised cause of mortality and long-term neurological morbidity in children. A significant number of these events appear to be caused by thromboembolic disease and, as with other childhood thrombotic problems, the incidence of central nervous system events appears highest during the neonatal period. In contrast to peripheral arterial and venous thrombotic problems, it is likely that a proportion of cerebral thromboembolic events occur either in utero or perinatally and reflect different risk factors from those occurring in older infants and children. The pathophysiology of perinatal stroke is complex and in many cases is likely to be multifactorial. It is now recognised that risk factors may relate to both maternal and placental problems as well as fetal and neonatal disorders. Large prospective studies of perinatal stroke are currently lacking and efforts to define the relative contribution from each of these areas are at an early stage. The complex nature of these disorders requires collaboration between a number of different disciplines including obstetrics, fetal medicine, pathology, neonatology and neurology. Of particular interest to haematologists is the possible impact of prothrombotic abnormalities in the pathophysiology of these events and also the potential for the use of antithrombotic agents in both management and prevention.

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

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.

PATIENTS AND METHODS

Four patients with neonatal stroke presenting as seizures were examined using a standard MRI protocol including diffusion-weighted images (DWI) and magnetic resonance angiography (MRA) within 72 h of birth. The time between the onset of symptoms and MRI ranged from 6 h to 48 h. Follow-up examinations were performed on days 5 ( n=1), 7 ( n=2), and 14 ( n=1) for the control of a treatment with low-molecular heparin.

RESULTS

Eight infarctions were detected in the four patients, 5 in the middle cerebral artery (MCA), three in the posterior cerebral artery (PCA) territory. All lesions were visible using DWI, four on T2-weighted images. Whereas in two patients small lesions contralateral to a large stroke were missed on T2-weighted images, the diagnosis would have been missed altogether without DWI in one patient. On follow-up, the visibility of the infarctions had declined using DWI after 5 days and the lesions were invisible after 1 week. Fourteen days after the stroke, an increased diffusion was detected in the infarcted brain tissue. By this time, all lesions were visible on T2-weighted images.

CONCLUSION

In neonates, infarcted brain tissue can be detected using DWI with high sensitivity during the first 2 days after stroke and before other sequences are diagnostic. However, the diffusion restriction does not persist beyond 1 week. After 5 days, diagnosis has to rest mainly on T2-weighted images.

Focal Cerebral Infarction in Newborn: Description of Three Cases

We observed 3 full-term newborns with focal ischemic injury of the middle cerebral artery (MCA), in which diagnosis of MCA stroke was suspected by US and confirmed by CT scan and MRI. A four-year follow-up was carried out to study the effect of neonatal stroke on neurodevelopmental outcome. All children had a history of pre-perinatal risk factors: neonatal cerebral infarction in term infants, in fact, has many possible causes, including bacterial meningitis, inherited or acquired coagulopathies, trauma and hypoxia-ischemia. The prognosis of neonatal MCA infarction depends on early diagnosis, on the CNS plasticity mechanism and, finally, on medical therapy and neuropsychological rehabilitation.

Selection of the optimum b factor for diffusion-weighted magnetic resonance imaging assessment of ischemic stroke

The purpose of this study was to determine the diffusion sensitivity factor b that optimizes the contrast-to-noise ratio (CNR) for both diffusion-weighted signal intensity and the apparent diffusion coefficient (ADCNR) when evaluating ischemic stroke by diffusion-weighted MRI. The relative contrast, noise levels, CNR, and ADCNR were calculated for typical ADC values in human brain, 780 microm(2)/s in adults and 1200 microm(2)/s in neonates in normal tissue, 20-40% less in acute and subacute stroke, and 50% more in chronic stroke. The optimum b factor depends strongly on the ADC, whether TE is fixed or varies with the b factor, whether CNR or ADCNR is measured, and anisotropy. The optimum b factor in adults is 1000 s/mm(2) in acute and chronic stroke, and 1200 s/mm(2) in subacute stroke. The optimum values are about 200 s/mm(2) lower in neonates than in adults. The CNR and ADCNR are within 10% of the optimum over at least a 2-fold range of b factors, from 68-136% of the optimum b factor. If a single b factor is to be used for all situations, a diffusion b factor of 1000 s/mm(2) is recommended.

Periventricular low intensities on fluid attenuated inversion recovery imaging in the newborn infant: Relationships to chronic white matter lesions

BACKGROUND

Neurological disadvantages due to hypoxic ischemic encephalopathy (HIE) are still very serious problems. In order to support the infant with HIE, it is important to evaluate the severity of the brain injury early. The authors performed a magnetic resonance imaging (MRI) study of the neonatal brain in order to assess the clinical value of periventricular low intensities (PVLI) detected on fluid attenuated inversion recovery (FLAIR) imaging.

METHODS

A total of 451 MRI from 167 preterm and 113 term infants were sorted into groups according to the corrected age at the time of scanning. Intensities in the white matter were then divided into five grades according to the severity of the finding on FLAIR imaging. Chronic abnormalities such as periventricular hyperintensities (PVHI) were also analyzed.

RESULTS

In early MRI, which was obtained before 2 months corrected age, the incidence of PVLI was 63%, while it was only 3% and 0% in the middle (2-8 months) and the late (8-18 months) scans, respectively. Instead of PVLI, PVHI were commonly observed both on late FLAIR imaging (89%) and late T2-weighted imaging (72%). The severity of the white matter damage diagnosed on early FLAIR imaging had a significant correlation with that of late FLAIR imaging.

CONCLUSIONS

F-PVLI on early FLAIR imaging would be a good predictor of chronic white matter damage. FLAIR imaging would be also useful in follow-up of infants because of its high sensitivity to the chronic white matter lesion.

Epidemiology of perinatal stroke

Perinatal stroke has become increasingly recognized, but the incidence is probably underestimated because of variation in the presentation, evaluation, and diagnosis. Based on estimates from population-based studies of infants with seizures, perinatal stroke occurs in approximately 1 in 4000 term births. Most perinatal strokes involve the middle cerebral artery and are caused by thromboembolism from an intracranial or extracranial vessel, the heart, or the placenta. Cardiac disorders, coagulation abnormalities, and infection are risk factors for stroke in the perinatal period. This article discusses the epidemiology of ischemic stroke occurring in the perinatal and neonatal period, including cerebrovascular events that are diagnosed during the perinatal period and those diagnosed retrospectively, when evidence of hemiparesis or postneonatal seizures leads to later evaluation and neuroimaging.