▶ Axial T1-weighted (left) and axial T2-weighted (right) images show abnormal hyperintense signal in the ventrolateral thalami (arrow) and posterolateral putamina (arrowhead).
If the patient presents in the first 24 hours of life, HII is most likely, but if symptoms arise later in the perinatal period, the differential diagnostic considerations include meningitis, hypoglycemia, kernicterus, and metabolic disorders.
▶ Hypoxia and hypotension both cause brain injury in infants. The pattern of injury depends on the severity and duration of the insult as well as on the degree of brain maturation. The imaging appearance also depends upon the timing of imaging relative to the inciting event.
▶ In mild to moderate insults, blood is shunted to vital structures and the cortical and subcortical portions of the boundary or “watershed” zones between arterial territories are affected. For term infants, these are the parasagittal border zones as in older children and adults. For premature infants (〈36 weeks), the boundary zone is the periventricular white matter and the resulting injury is periventricular leukomalacia.
▶ Profound insults primarily affect regions of high metabolic activity, which are also the areas of early myelination. In all infants, these include the posterolateral putamina, ventrolateral thalami, posterior limb of the internal capsule, perirolandic gyri, posterior brainstem, corona radiata, and cerebellar vermis.
▶ In profound perinatal hypoxia/hypotension MRI obtained within the first 24 hours may show normal findings on conventional images but reduced diffusion on diffusion-weighted sequences (DWI) and a lactate peak on MR spectroscopy (at 1.3 ppm at 1.5T) in affected areas. Early in the first week, T1- and T2-hyperintensity is observed in affected areas, but later in the first week or early second week, T2-shortening is noted.
1. Huang BY, Castillo M. Hypoxic-ischemic brain injury: Imaging findings from birth to adulthood. Radiographics. 2008 Mar–Apr;28(2):417–439.Find this resource:
2. Chao CP, Zaleski CG, Patton AC. Neonatal hypoxic-ischemic encephalopathy: multimodality imaging findings. Radiographics. 2006 Oct;26 Suppl 1:S159–S172.Find this resource: