Relation between the date of cyst formation observable on ultrasonography and the timing of injury determined by serial electroencephalography in preterm infants with periventricular leukomalacia

The aim of this study was to clarify the relation between the date of cyst formation and the timing of injury in preterm infants with periventricular leukomalacia in order to address the issue of whether or not we can determine the timing of injury on the basis of ultrasonographic findings. We studied 33 preterm infants with cystic periventricular leukomalacia, the gestational ages being 32 weeks or less. As 27 of them exhibited either acute or chronic stage abnormalities in the initial electroencephalogram, the timing of injury was presumed to be before or around birth. For the remaining six infants, the timing of injury was considered to be postnatal in two infants, and was not determined in another four. The median date of cyst formation was 18 days of age (range, 10–39 days) in the 27 infants with abnormal initial electroencephalograms. For these 27 infants, the gestational age did not influence the date of cyst formation. In contrast, the date of cyst formation was significantly earlier in infants with widespread cysts than in those with localized cysts. In conclusion, it is difficult to determine the timing of injury from ultrasonographic findings, because the range of the date of cyst formation on ultrasonography was very wide among infants whose timing of injury was not greatly different.