Magnetic resonance imaging in perinatal asphyxia.

Correspondence to: Dr Ernst Martin, University Children's Hospital Magnetic Resonance Unit, Steinwiesstrasse 75, CH8032 Zurich, Switzerland. Introduction The purpose of this review article is: (i) to recall the impact of perinatal asphyxia and its consequences on child development; (ii) to establish the diagnostic benefit of magnetic resonance imaging (MRI) and to compare it with other imaging modalities; (iii) to summarise the range of imaging patterns viewed on different brain scans and to discuss their aetiology; (iv) to describe the evolution of characteristic MRI findings observed during the early postnatal period and during later childhood; and (v) to estimate the role of MRI in predicting later neurodevelopmental outcome. Acute perinatal asphyxia refers to a condition of hypoxaemia, hypercapnia and insufficient blood perfusion of the newborn during labour and birth. It is considered to be the 'single most important perinatal cause of neurological morbidity'.' Perinatal asphyxia and its consequences have an incidence of 2-9%o, in term neonates,2 which is very much higher in premature babies, causing not only neurological impairment, but also behavioural problems and intellectual deficits.3 Depressed fetal heart rate, meconium stained amniotic fluid, low Apgar scores, low scalp and cord pH, or clinical signs of neurological depression soon after birth signify the acute clinical condition of the newborn. The predictive value of the clinical features for later neurodevelopmental outcome is, however, rather disappointing. Affected neonates present with a characteristic, although non-specific, syndrome called hypoxic-ischaemic encephalopathy (HIE). They may be initially hyperalert, or often lethargic, with diminished muscle tone and spontaneous movements. They demonstrate poor suck, apnoea, and other signs of brainstem dysfunction, or in severe cases, they are comatose, with seizures beginning within hours of birth. The death rate in term infants with HIE is around 11%, and as many as 60% of affected premature newborns die. Moreover, 20-30% of survivors suffer from mental retardation, cerebral palsy, and seizure disorders in later childhood.3 Despite major advances in obstetric and neonatal care, the prevalence of cerebral palsy has not decreased over the past decade.4 About 10-15% of children who later develop cerebral palsy have intrapartum insults with symptoms of HIE during the first week of life. In an appreciable number of children with cerebral palsy in utero hypoxia-ischaemia must therefore have preceded the perinatal period, which caused neither maternal symptoms nor relevant HIE in the newborn.56 Sarnat has developed a grading system for HIE, based on neurological evaluation in the newborn period, which helps to differentiate babies with favourable outcome from those with a poor prognosis for developing neurological sequelae.7 Although it has been of great prognostic value for infants with mild HIE and those with severe encephalopathy, the prognosis of moderately affected infants is less certain. Moreover, many babies with HIE require intensive care and artificial ventilation during the first days of life, and are not accessible to clinical evaluation.