Temporal evolution of hypoxic-ischaemic brain lesions in asphyxiated full-term newborns as assessed by computerized tomography.

Hypoxic-ischaemic brain lesions may be detected as low density (LD) areas by means of computerized tomography (CT), but the clinical significance of such LD areas has been controversial. Since timing might be a critical factor, we studied the temporal evolution of LD areas in 9 asphyxiated term babies who had had two or more CT, and compared the changes to the neurodevelopmental outcome. Scans were classified according to the elapsed time after asphyxia as early (day 1-7, n = 6), intermediate (week 2-4, n = 7; week 4-7, n = 3) and late CT (3 months or more, n = 7). In early scans, no, or only ill defined, LD areas were seen in the periventricular region. In intermediate CT's, LD-zones were further diminished in those babies who later were normal. Sharply accentuated LD areas, however, appeared in those who later suffered from neurodevelopmental disorders. These LD areas, probably representing hypoxic-ischaemic lesions, were located periventricularly, extending into the subcortical white matter and the cortex, and usually involved both hemispheres symmetrically. They began to disappear at 4 to 7 weeks in some regions, possibly because of glial proliferation. LD persisting more than 4-7 weeks tended to transform into cyst-like lesions, or marked atrophy. We conclude (1) that hypoxic-ischaemic lesions appear as zones of low density on CT scans performed after the first week and (2) that the extent of such lesions can best be assessed between 9 to 23 days after asphyxia.