MR imaging of fetal brain malformations.

METHODS: From the generally accepted data on the morphogenesis of the brain, the principles for the classification of brain malformations are given, and the salient features of each malformation which may be considered as independent from the developmental stage and therefore practical for MR imaging in the fetus after mid-gestation, are discussed. RESULTS AND DISCUSSION: However, the correlation with the clinical results in 150 cases of malformations out of a series of more than 1,000 cases of MR fetal brain imaging, demonstrates that beside the main, well-defined malformative entities, a significant degree of uncertainty remains. As the indication of further imaging is mainly based on the ultrasonographic findings, cases that are not identified as abnormal by US are not submitted to MRI (partial commissural agenesis and malformations of cortical development). A striking discrepancy exists between the findings of US and those of MRI, in the specific instance of the disorders of the posterior fossa (cystic malformations versus mega cisterna magna versus cerebellar defects), which may be only partly corrected by the use of strict anatomic criteria. Similar difficulties are observed for the diagnosis of nondestructive microcephaly.
CONCLUSION: Long-term prospective longitudinal clinical-radiological studies of these groups of patients are needed.