Question

Discuss the neuro-imaging features of hypoxic ischemic encephalopathy (HIE) in term and preterm births. [5+5]

Hint:

In term infants, MRI typically reveals basal ganglia, thalamic, and cortical injuries in HIE, while preterm infants often exhibit intraventricular hemorrhage (IVH) and periventricular leukomalacia (PVL) due to their immature vascular and brain structures.

Answer 1

Step 1: Introduction to Hypoxic Ischemic Encephalopathy (HIE).
Hypoxic ischemic encephalopathy (HIE) is a neurological condition that results from insufficient oxygen and blood flow to the brain, typically occurring during labor and delivery. HIE can lead to cerebral injury and neurological impairments ranging from mild developmental delays to severe disabilities or death. The degree of injury and its effects vary depending on the timing, severity, and duration of the hypoxic event. Neuro-imaging plays a crucial role in identifying and assessing the extent of brain injury caused by hypoxia-ischemia, especially in neonates who present with clinical signs of neurological dysfunction after birth. The most common imaging modalities used in HIE are cranial ultrasound, magnetic resonance imaging (MRI), and computed tomography (CT).
Step 2: Neuro-imaging Features of HIE in Term Infants.
(1) MRI Features in Term Infants: - Timing and Extent of Injury: MRI is the most sensitive imaging modality for assessing hypoxic-ischemic injury in term infants. The timing of the injury relative to birth is critical in determining the pattern and distribution of brain injury. MRI findings in term infants with HIE can include: - Basal ganglia and thalamic lesions: These areas are the most commonly affected due to their vulnerability to hypoxic-ischemic injury. MRI shows bilateral symmetric lesions in the putamen, globus pallidus, and thalamus, which are hyperintense on T1-weighted images and hypointense on T2-weighted images. - Cortex and white matter injury: In more severe cases, the cerebral cortex and white matter can also be affected. MRI may reveal cortical laminar necrosis (loss of neurons in the cortical layers), white matter edema, or necrosis. - Posterior limb of the internal capsule: Lesions in this area, especially the posterior limb, are often associated with severe injury and are seen as low signal intensity on T2-weighted MRI, indicating axonal injury. - Pattern of injury: The watershed areas of the brain, which lie between the main vascular territories, are especially susceptible to hypoxic-ischemic injury. These areas are typically located cortically, leading to cortical infarctions visible on MRI. - Cerebellum: In severe cases of HIE, the cerebellum may also show evidence of neurodegeneration, appearing hypointense on T2-weighted imaging.
(2) CT Scan Features in Term Infants: - CT scan is not as sensitive as MRI for detecting early HIE but can still show increased density in the affected brain regions, especially if there is acute hemorrhage or infarction. - Edema in the periventricular or subcortical areas may also be seen, and in later stages, ventricular dilation may develop as a result of brain atrophy.
Step 3: Neuro-imaging Features of HIE in Preterm Infants.
(1) MRI Features in Preterm Infants: - Injury in Preterm Infants: The neuro-imaging features of HIE in preterm infants often differ from those seen in term infants. Preterm infants are more vulnerable to intraventricular hemorrhage (IVH) and periventricular leukomalacia (PVL) due to their underdeveloped brain structure. - Intraventricular Hemorrhage (IVH): IVH is a common manifestation of HIE in preterm infants, especially those born before 32 weeks gestation. MRI shows hypointense areas in the ventricles, indicating blood or clot formation. More severe cases may lead to ventricular dilatation or post-hemorrhagic hydrocephalus. - Periventricular Leukomalacia (PVL): PVL is another common finding in preterm infants and is a form of white matter injury. MRI shows cystic lesions in the periventricular white matter that appear hyperintense on T2-weighted images. PVL is associated with necrosis of the white matter around the ventricles and is often linked with motor impairments such as cerebral palsy. - Cerebellar Injury: In preterm infants, the cerebellum may also be affected by HIE, showing shrinkage or hypoplasia on MRI due to impaired development and ischemia. - Basal Ganglia and Thalamus: As in term infants, the basal ganglia and thalamus may show injury, but this is less common in preterm infants than in term infants, who have more mature brain structures.
(2) CT Scan Features in Preterm Infants: - CT scan in preterm infants often shows intraventricular hemorrhage or parenchymal hemorrhage in periventricular or subcortical regions. As with term infants, ventricular dilatation and brain atrophy may be noted in later stages, indicating progressive damage.
Step 4: Differences in Imaging Findings Between Term and Preterm Infants.
- In term infants, HIE predominantly affects the basal ganglia, thalamus, and cortex, with watershed areas and white matter being more involved. - In preterm infants, the most common findings are intraventricular hemorrhage and periventricular leukomalacia, with less involvement of the basal ganglia and thalamus.