Presentation
Seizures.
Patient Data
T1 hyperintensities are seen in bilateral posterior putamina and ventrolateral thalami. Myelination of the posterior limbs of bilateral internal capsules is not well appreciable on T1 or T2 images.
Case Discussion
Findings are suggestive of hypoxic-ischemic encephalopathy. The patient had a history of birth asphyxia.
The lack of proper visualization of the posterior limb of the internal capsule is called an absent posterior limb sign and is one of the main MRI findings of prognostic significance in term neonates with suspected hypoxic-ischemic brain injury. An absent posterior limb sign is defined as loss of the normally distinct hyperintensity on T1 images in the posterior part of the posterior limb of the internal capsule in neonates born at term (>37 weeks gestation).
The signal intensity of the posterior limb of the internal capsule can be compared to that of the posterolateral putamen, which is normally less intense than the posterior third-to-half of the posterior limb of the internal capsule due to the latter's myelination; this relationship is inverted in hypoxic-ischemic injury. Correlation with T2-weighted images can help localize the posterior limb of the internal capsule and show loss of the normal T2 hypointense focus in the same locale.
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