Chiari malformations Chiari I malformation involves herniation of the peg-like cerebellar tonsils into the foramen magnum (>5 mm in patients <15 years old), and is associated with syringomyelia. Chiari II malformation is more severe, involving herniation of the medulla and vermis and elongation and downward displacement of the brainstem. This malformation is virtually always associated with …
How does the premature brain respond to ischemic injury? Periventricular leukomalacia (PVL) is characterized by ischemia in an end arterial distribution (in the watershed regions of white matter that surround the ventricles). US may demonstrate an increase in periventricular echogenicity soon after the initial insult. Cystic change in these regions can be seen later in …
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Classification of germinal matrix hemorrhage The germinal matrix lies in the caudothalamic groove. This is a highly vascular region of the prenatal and premature brain and is prone to hemorrhage, with rupture of the thin venules subsequent to decreased perfusion or oxygenation. Morbidity and mortality may be predicted based on the grade of the hemorrhage: …
What is the differential diagnosis for what appears to be massively dilated ventricles on a prenatal ultrasonography (US) or MRI examination? The appearance of massively dilated ventricles may be secondary to holoprosencephaly, hydranencephaly, or hydrocephalus. Hydranencephaly results from massive necrosis of the cerebral hemispheres and may be secondary to vascular disease with bilateral internal carotid …
Holoprosencephalies Holoprosencephaly refers to incomplete differentiation of the fetal prosencephalon (forebrain) into separate hemispheres. Holoprosencephaly may manifest as alobar , resulting in one posteriorly located monoventricle (versus the normally separated two lateral ventricles) and fusion of the thalami; semilobar , with two hemispheres posteriorly but not anteriorly; or lobar, with only mild frontal abnormalities. The middle interhemispheric variant has …
What are migrational anomalies of the central nervous system (CNS)? Normal neuronal migration occurs during fetal brain development as neurons migrate from the germinal matrix to the cortex along radial glial fibers. Partial or total arrest of this process leads to a migrational anomaly. These anomalies include the following: • Focal cortical dysplasia (subtle subcortical high …
Myelinated brain versus nonmyelinated brain on MRI How does myelinated brain differ from nonmyelinated brain on an infant magnetic resonance imaging (MRI) examination? Where does one expect to see myelinization occur first? Myelinated brain white matter, as in adults, appears hyperintense relative to gray matter on T1-weighted MR images and hypointense on T2-weighted images. In …
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