Diffusion- and T2-weighted increases in magnetic resonance images of immature brain during hypoxia-ischemia:: Transient reversal posthypoxia

Hypoxic-ischemic changes in brain are detected earlier with diffusion-weighted (DW) than with T-2-weighted magnetic resonance (MR) imaging techniques in adults, whereas the response in immature brain is not known. We investigated MR imaging changes prior to, during, and/or after 2 h of hypoxia-ischemia (right carotid artery occlusion + 2 h of hypoxia) in 7-day-old rats anesthetized with isoflurane. In general, within the first 45 min of hypoxia-ischemia there were no changes in the DW or T-2-weighted images. By the second hour of hypoxia-ischemia there were marked areas of increased intensity in both the T-2 and the DW images, with cortex and striatum being affected prior to thalamus and hippocampus. The area of DW exceeded that of T-2 hyperintensities. In the first hour after hypoxia-ischemia there was a transient recovery of hyperintensities on both T-2 and DW images. Between 24 and 72 h the hyperintense area on DW images decreased, whereas that on T-2-weighted images increased. The distribution of pathological damage assessed histologically correlated with the areas of hyperintensity on the MR images. In contrast to adult brain, early hypoxic-ischemic injury in immature brain is detected as an increase in intensity in both diffusion- and T-2-weighted images, indicating a unique alteration in brain water dynamics in this neonatal model of hypoxia-ischemia. These imaging changes and alterations in brain water can rapidly but transiently reverse upon the start of normoxia and reperfusion, suggestive of secondary energy failure or delayed neuronal death.