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On routine prenatal ultrasonography, the cavum septum pellucidum was absent and a possible posterior fossa malformation was noted in a 31-week male fetus with a normal karyotype. A magnetic resonance imaging (MRI) study demonstrated the absence of most of the corpus callosum (midline sagittal image, Panel A), except for a small component of the anterior body (arrow). A coronal image (Panel B) shows the classic contour of nonconverging lateral ventricles (the asterisk indicates the third ventricle). The remainder of the brain, including the posterior fossa, appeared normal.
Dysgenesis of the corpus callosum is a relatively frequent cerebral malformation. It is usually sporadic and may be an isolated anomaly. Although it may be asymptomatic postnatally, it is considered a potential marker of neurologic impairment. The prenatal detection of other cerebral malformations indicates a poor prognosis.
Callosal dysgenesis is inferred ultrasonographically from the absence of the cavum septum pellucidum but is often a difficult diagnosis to make. In addition, skull ossification and reduced tissue contrast limit ultrasonographic detection of subtle associated anomalies. Fetal MRI may provide information in addition to that provided by the ultrasonographic examination, allowing a better determination of the prognosis. A postnatal ultrasonographic study confirmed the dysgenesis of the corpus callosum. No other abnormalities were noted on neonatal examination, and at the age of one year, the child is neurologically normal. The absence of additional brain malformations predicted the good postnatal outcome.
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