Diffusion restriction in the corticospinal tract and the corpus callosum of term neonates with hypoxic-ischemic encephalopathy

Background: Diffusion-weighted imaging performed shortly after brain injury has been shown to facilitate visualization of acute corticospinal tract injury known as "pre-Wallerian degeneration."

Objective: The aim of this study was to determine whether diffusion restriction in the corticospinal tract and corpus callosum occurs within the first 2 weeks after birth in neonates with neonatal hypoxic-ischemic encephalopathy.

Materials and methods: We enrolled a consecutive series of 66 infants diagnosed with hypoxic-ischemic encephalopathy who underwent MRI. We evaluated diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) values to assess the presence of restricted diffusion in the corticospinal tract and corpus callosum. Next, we compared ADC values in the corticospinal tract and in the splenium and genu of the corpus callosum of infants with abnormal pattern on MRI with those of control infants, who showed a normal pattern on MRI. We attempted to follow all infants with hypoxic-ischemic encephalopathy until 18 months of age and assess them using a standardized neurologic examination.

Results: After exclusions, we recruited 25 infants with abnormal MRI and 20 with normal MRI (controls). Among these 45 neonates, pre-Wallerian degeneration was visualized in the corticospinal tract in 10 neonates and in the corpus callosum in 12. The ADC values in the corticospinal tract in the first week were significantly lower than they were in the second week. Infants with pre-Wallerian degeneration in the corticospinal tract showed an unfavorable outcome.

Conclusion: Pre-Wallerian degeneration was visualized in the corticospinal tract and corpus callosum and was associated with extensive brain injury caused by hypoxic-ischemic encephalopathy. The changes in signal were observed to evolve over time within the first 2 weeks. The clinical outcome of infants having pre-Wallerian degeneration in the corticospinal tract was unfavorable.