HYPOXIC-ISCHEMIC INJURY

Imaging

Imaging for optimized detection of hypoxic-ischemic brain injury:

CT may show changes in hypoxic-ischemic brain injury, however MRI is the imaging of choice for assessing the detail of the acute hypoxic-ischemic changes, and the long-term structural sequelae in patients who have subsequent epilepsy. MRI should include thin slice volumetric T1-weighted images, axial and coronal T2-weighted and FLAIR images. In acute hypoxia-ischemia, diffusion-weighted imaging and ADC maps may be required to show areas of ischemia in the first hours after the injury.

Imaging characteristics of acute hypoxic-ischemic injury:

• diffusion restriction, resulting in high signal on DWI and low signal on ADC maps, within minutes from the onset of hypoxia-ischemia
• high signal on T2/FLAIR imaging in the affected area within 6-12 hours
• sulcal effacement and mass effect in the affected area in the first 24-48 hours
• cortical laminar necrosis appearing as a ribbon of high signal on T1 weighted images, after 2 weeks
• distribution of changes depend on the contributions of hypoxia and/or ischemia (perfusion) to the injury, and on age (watershed territory distribution differs in the immature brain compared to the mature adult brain)

Imaging characteristics of chronic hypoxic-ischemic injury:

• atrophy, gliosis, porencephaly/encephalomalacia and ex vacuo dilation of the ipsilateral ventricle in the location of the previous acute hypoxic-ischemic injury.