Head Ultrasound in Neonatal Hypoxic-Ischemic Injury and Its Mimickers for Clinicians: A Review of the Patterns of Injury and the Evolution of Findings over Time

Hypoxic-ischemic injury (HII) of the neonatal brain and resulting clinical hypoxic-ischemic encephalopathy remains a significant cause of morbidity and mortality in the neonatal population. Ultrasound (US) has emerged as a powerful screening tool for evaluation of a neonate with suspected HII. The pattern of injury on brain imaging has crucial implications in therapies and predicted neurodevelopmental outcomes. US has become increasingly effective at determining the pattern, timing, and extent of injury in HII as well as differentiating these findings from a host of diagnoses that can result in a similarly appearing clinical picture. Repeated US studies over a patient's course can define the evolution of findings from the acute through chronic phase in addition to identifying any complications of therapy. US also has the added benefits of easy portability, no need for patient sedation, and a relatively low cost when compared to other imaging modalities like magnetic resonance imaging (MRI). It is crucial that clinicians understand the full capabilities of advanced US in identifying an underlying diagnosis, directing appropriate therapy, monitoring disease progress, and finally in predicting outcomes, thus improving the care of neonates with encephalopathy. The following article demonstrates the breadth of uses for US in the full-term neonate with encephalopathy, its limitations, the patterns of injury seen, and their evolution over time. We will also briefly review several clinical mimickers of HII for comparison.