J. M. Pennock

Abnormal Magnetic Resonance Signal in the Internal Capsule Predicts Poor Neurodevelopmental Outcome in Infants With Hypoxic-Ischemic Encephalopathy

Objective. The aim of this study was to establish whether abnormal signal intensity in the posterior limb of the internal capsule (PLIC) on magnetic resonance imaging is an accurate predictor of neurodevelopmental outcome at 1 year of age in infants with hypoxic-ischemic encephalopathy (HIE). Methods. We have examined 73 term neonates with HIE between 1 and 17 days after birth with cranial magnetic resonance imaging and related the magnetic resonance imaging findings to neurodevelopmental outcome at 1 year of age. Results. All infants with an abnormal signal intensity in the PLIC developed neurodevelopmental impairment although in 4 infants with very early scans the abnormal signal was not apparent until up to 4 days after birth. A normal signal intensity was associated with a normal outcome in all but 4 cases; 3 of these infants had minor impairments and all had persistent imaging changes within the white matter. The 4th infant with a normal signal intensity on day 2 died before a further image could be obtained. The absence of normal signal predicted abnormal outcome in term infants with HIE with a sensitivity of 0.90, a specificity of 1.0, a positive predictive value of 1.0, and a negative predictive value of 0.87. The test correctly predicted outcome in 93% of infants with grade II HIE, according to the Sarnat system. Applying a Bayesian approach, the predictive probability of the test (the probability that the test would predict an outcome correctly) was distributed with a mean of 0.94 and 95% confidence limits of 0.89 to 1.0. Conclusion. Abnormal signal intensity in the PLIC is an accurate predictor of neurodevelopmental outcome in term infants suffering HIE.

Use of fluid attenuated inversion recovery (FLAIR) pulse sequences in MRI of the brain

Fluid attenuated inversion recovery pulse sequences with a long echo time (TE) have been used to image the brain in one volunteer and four patients. The long inversion time used with this sequence suppresses the signal from CSF and the long TE produces very heavy T2 weighting. The marked reduction in flow artefact from CSF and the high T2 weighting enabled anatomical detail to be seen within the brain stem and produced high lesion contrast in areas close to CSF. Lesions were demonstrated with greater conspicuity than with conventional T2-weighted sequences in patients with cerebral infarction, low grade astrocytoma, and diplegia.

MR imaging of anisotropically restricted diffusion of water in the nervous system: technical, anatomic, and pathologic considerations.

The use of MR imaging to image anisotropically restricted diffusion (ARD) of water in the nervous system is described. The theoretical basis for the use of the pulsed gradient spin echo sequences is outlined, including an estimate of the range of cell dimensions that can be studied with this technique. The importance of restricted diffusion across myelinated white matter fibre tracts is emphasised and the capacity of MR imaging to demonstrate fibre pathways as a function of their direction is illustrated. Technical developments that have been implemented include 256 x 256 spatial resolution, a wider range of diffusion times Td, and an increased range of diffusion sensitivity parameters b. Effects of these are illustrated together with the use of gradient moment nulling methods, oblique sensitisation, and a smaller set of gradient coils that enable shorter values of echo time to be used with the same value of b. The anatomical basis for ARD imaging is analysed, and association, commissural, and projection fibre tracts are demonstrated in different planes. The published literature on variations of the apparent diffusion coefficient from normal is reviewed and examples where diffusion weighted images revealed information that was not necessarily apparent with conventional sequences are illustrated. These include cases of multiple sclerosis, chronic head injury, progressive multifocal leucoencephalopathy, cerebrovascular disease, astrocytoma, and probable metastases to the brain. Imaging of ARD affords a fascinating conjunction between the microscopic movement of water, the properties of myelinated white matter fibres, gross anatomy of the brain, and changes of the diffusion of water in disease.

Hypoxic-ischaemic encephalopathy: early and late magnetic resonance imaging findings in relation to outcome.

Sixteen infants with hypoxic-ischaemic encephalopathy (HIE) were studied using serial magnetic resonance imaging (MRI) up to the age of 2 years. The infants had regular neurological and developmental assessments. An nuclear magnetic resonance (NMR) score was devised to quantify the early and late MRI findings and a neurological optimality score was used to quantify abnormal neurological signs at the time of the final examination. The follow up MRI score was compared with the neonatal MRI score and the outcome of the child. There was a strong positive correlation between the neonatal and follow up MRI scores and between MRI scores and optimality score. All infants with a normal outcome had patchy white matter abnormalities. All infants with an abnormal outcome had extensive white matter abnormalities. The outcome was most severe in those infants with additional basal ganglia atrophy with or without cyst formation. Infants with mild HIE who are developmentally normal at the age of 2 years do not have normal MRI scans and may be at risk of minor neurological problems by school age. Bilateral basal ganglia abnormalities are associated with severe developmental delay, but infants with mainly white matter and cortical abnormalities have less severe problems despite extensive tissue loss.

Enhancement of relaxation rate with paramagnetic contrast agents in NMR imaging

Enhancement of spin-lattice relaxation using oral ferric chloride and using inhaled oxygen is illustrated. A 0.06% solution of ferric chloride reduced the spin-lattice relaxation time in the fundus of the stomach from 730 ms to 285 ms. Ferric chloride may be useful as a bowel-labeling agent. In 5 volunteers inhalation of 100% oxygen decreased the mean observed spin-lattice relaxation time of blood within the left ventricular cavity. Although the change was small, it may have important uses in monitoring metabolic processes.

Patterns Of Visual Impairment Associated With Lesions Of The Preterm Infant Bran

The visual function of 42 children with hacmorrhagic and/or ischaemic cerebral lesions acquired before a gestational age of 35 weeks was examined and related to cranial ultrasound in the neonatal period and to MR1 and neurodevelopmental status at follow‐up. All 37 children with abnormal ultrasound scans and one of the five with normal ultrasound scans showed impairment of one or more aspects of visual function. While impaired acuity was more frequent among infants with MRI evidence of visual pathway damage, this was not an invariable finding. Normal or near‐normal visual acuity did not preclude the presence of other functional visual deficits. The authors conclude that preterm cerebral insults may produce a variety of visual difficulties, the pattern and severity of which cannot be predicted on imaging. Each child therefore requires individual assessment of multiple aspects of visual function.

IMAGING OF THE BRAIN BY NUCLEAR MAGNETIC RESONANCE

A nuclear magnetic resonance (NMR) machine constructed by Thorn-EMI Ltd was used to produce tomographic images of the brain in eight volunteers and fourteen patients. The use of an inversion recovery technique designed to emphasise variations in the spin-lattice time constant (T1) resulted in remarkable differentiation between grey and white matter in all subjects examined. White matter was seen both centrally and peripherally to subcortical level and the basal ganglia were clearly demarcated by the surrounding white matter and ventricular system. The posterior fossa was visualised with substantially less artefact than with X-ray computed tomography (CT) and both the brainstem and middle cerebellar peduncle were clearly shown. Pathological appearances in patients with glioblastoma multiforme, cerebral infarction, and cerebral aneurysm were demonstrated and compared with those seen with CT. The technique will require thorough clinical evaluation but appears to have considerable potential in the diagnosis of neurological disease.

Ischaemic and haemorrhagic brain lesions in newborns with seizures and normal Apgar scores.

Serial ultrasound scans and conventional and diffusion weighted magnetic resonance imaging (MRI) were performed on 16 neonates who presented with seizures. The Apgar scores were normal and subsequently no metabolic or infective cause could be found. The aim of the study was to evaluate the extent to which early sequential imaging can elucidate the cause of seizures in apparently neurologically normal infants. Fourteen of the infants had haemorrhagic or ischaemic lesions on MRI and these were detected by ultrasound scanning in 11. Early ultrasound scanning detected the haemorrhagic lesions but the ischaemic lesions were often not seen until the end of the first week of life. Early MRI, however, was able to detect all the ischaemic lesions. The evolution of the insult could be timed by using serial ultrasound scans and a combination of diffusion weighted and conventional MRI during the first week of life, confirming a perinatal insult even in the absence of fetal distress. Although the aetiology of these lesions remains obscure, serial ultrasound scans will detect the presence of cerebral lesions in neonates presenting with isolated seizures but additional MRI sequences will give better definition on type, site, and extent of the pathology.

Merosin-deficient congenital muscular dystrophy: the spectrum of brain involvement on magnetic resonance imaging

Children with merosin-deficient congenital muscular dystrophy (CMD) have striking white matter changes on T-2 weighted brain magnetic resonance imaging (MRI). There have been occasional cases with structural abnormalities, mainly involving the occipital cortex. We report our brain imaging findings in 14 children with merosin-deficient CMD. Ten cases had a severe reduction or absence of merosin on immunocytochemistry and four cases had partial reduction. All 14 cases had white matter changes, which appeared after the first 6 months of life and persisted with time. The changes were diffuse and the oldest child scanned (14 years) also showed involvement of the U fibres. Five children with total absence of merosin also had structural abnormalities. One child had moderate mental retardation and epilepsy, mainly characterised by complex partial seizures, with atypical absences, which had been difficult to treat. Brain MRI showed marked occipital agyria and pontocerebellar hypoplasia. The gyral pattern of the rest of the brain looked normal. The four other cases, all with normal intelligence, also had cerebellar hypoplasia with variable involvement of the pons. They did not, however, have neuronal migration defects. It is recognised that several forms of congenital muscular dystrophy, namely Fukuyama CMD, muscle-eye-brain disease and Walker-Warburg syndrome, have structural brain abnormalities and associated severe mental retardation. Our cases demonstrate that a range of structural malformations can also be found in a significant number of children with merosin-deficient CMD.

CRANIAL ULTRASOUND AND MAGNETIC RESONANCE IMAGING IN HYPOXIC‐ISCHAEMIC ENCEPHALOPATHY: A COMPARISON WITH OUTCOME

Forty term infants with hypoxic‐ischaemic encephalopathy were assessed during the neonatal period with cranial ultrasound and MRI, and the findings were compared with outcome at one year of age. 38 had abnormalities on ultrasound and all had changes on MRI. The incidence of changes in the basal banglia/thalami and periventricular white matter was much greater with MRI than with ultrasound. Changes in the basal ganglia and thalami on MRI were associated with a poor outcome if they had also been detected with ultrasound. However, MRI identified four small infarcts which were not detected by ultrasound. There was no consistent association between periventricular white matter change on MRI and outcome. Regular ultrasound scanning identified all infants with a poor outcome. A normal ultrasound or isolated findings of intraventricular haemorrhage, subarachnoid haemorrhage or transient flares were associated with a normal outcome in 13 of 14 infants.