Temporal dynamics of neonatal hypoxic-ischemic encephalopathy injuries on magnetic resonance imaging

Abstract

Moderate to severe perinatal hypoxic-ischemic encephalopathy occurs in ~ 1 to 3/1000 live births in high-income countries and is associated with a significant risk of death or neurodevelopmental disability. Detailed assessment is important to help identify high-risk infants, to help families, and to support appropriate interventions. A wide range of monitoring tools is available to assess changes over time, including urine and blood biomarkers, neurological examination, and electroencephalography. At present, magnetic resonance imaging is unique as although it is expensive and not suited to monitoring the early evolution of hypoxic-ischemic encephalopathy by a week of life it can provide direct insight into the anatomical changes in the brain after hypoxic-ischemic encephalopathy and so offers strong prognostic information on the long-term outcome after hypoxic-ischemic encephalopathy. This review investigated the temporal dynamics of neonatal hypoxic-ischemic encephalopathy injuries, with a particular emphasis on exploring the correlation between the prognostic implications of magnetic resonance imaging scans in the first week of life and their relationship to long-term outcome prediction, particularly for infants treated with therapeutic hypothermia. A comprehensive literature search, from 2016 to 2024, identified 20 pertinent articles. This review highlights that while the optimal timing of magnetic resonance imaging scans is not clear, overall, it suggests that magnetic resonance imaging within the first week of life provides strong prognostic accuracy. Many challenges limit the timing consistency, particularly the need for intensive care and clinical monitoring. Conversely, although most reports examined the prognostic value of scans taken between 4 and 10 days after birth, there is evidence from small numbers of cases that, at times, brain injury may continue to evolve for weeks after birth. This suggests that in the future it will be important to explore a wider range of times after hypoxic-ischemic encephalopathy to fully understand the optimal timing for predicting long-term outcomes.

Figure 1

Representative cases of T1, T2, and diffusion tensor imaging images with differing scores between early and later scans. In patient A, the basal ganglia score has increased on day 4 (score = 3, indicating signal abnormalities in both the thalamus [white arrow] and basal ganglia [black arrow]) compared to day 10 (score = 1, indicating signal abnormality limited to the thalamus [white arrow]). Similarly, in patient B, basal ganglia injury has been more prominent on day 5 (score = 4, indicating extensive involvement with signal abnormalities in the thalamus and basal ganglia [white arrows] and white matter tracts [black arrows]) compared to day 9 (score = 2, indicating reduced signal abnormalities in the thalamus and basal ganglia [white arrows]). Reprinted with permission from O’Kane et al. (2021). ADC: Apparent diffusion coefficient.

Figure 2

Exemplar case. Caption as cited in the reference: (A–F) Male neonate, born at 4 weeks and 6 days of gestation exhibited diffuse injuries on early magnetic resonance imaging (MRI) on day 4 (A–C) and late MRI on day 9 (D–F) and a favorable outcome as shown by normal neurological assessment at 23 months and a global developmental quotient of 97. (A, B) Early diffusion-weighted imaging and corresponding apparent diffusion coefficient maps with hyperintensity in the hippocampi (bottom arrows), the thalami (top arrows) (A), and the perirolandic, frontal and parietal white matter (arrows) (B). (C) Axial T1-weighted imaging with hyperintensity in the bilateral insular cortex (arrows). (D) Axial T2-weighted images on late MRI with mild hyperintensity in the thalami (arrows). (E, F) Axial T1-weighted images on late MRI with normal hyperintensity within the posterior limb of internal capsule (arrows), mild intraventricular hemorrhage in the left occipital ventricular horn (*) (E) and hyperintensity within the insular cortex (arrows) (F). Reprinted with permission from Charon et al. (2016).

Figure 3

Exemplar case. Caption as cited in the reference: (A–D) Female neonate, born at 39 weeks of gestation, who exhibited normal early magnetic resonance imaging (MRI), abnormal late MRI (moderate central lesions) and a favorable outcome. (A, B) Normal early imaging (day 5) at the level of the basal ganglia with axial diffusion-weighted imaging (A), and axial T2-weighted imaging (B); posterior limb of internal capsule signal intensity was normal (arrows). (C, D) Late imaging (day 12) at the same level with mild hyperintensity on axial T1-weighted images within the thalami (bottom arrows) and normal hyperintensity within the posterior limb of internal capsule (top arrows) (C) and axial T2-weighted images with hyperintensity within the thalami (bottom arrows) and the posterior part of the lentiform nuclei (top arrows) (D). Reprinted with permission from Charon et al. (2016).