MR imaging of fetal cerebral anomalies.

BACKGROUND: Prenatal diagnosis of fetal brain anomalies relies mainly upon ultrasonography. However, even in the most experienced hands, the technique has limitations for some difficult diagnoses. MRI is an excellent imaging modality for the paediatric and adult brain. OBJECTIVE: To assess the value of prenatal MRI when a cerebral anomaly was detected by US and where the prognosis depended on the identification of other anomalies undetectable by US, or where fetuses were at risk for a CNS lesion even when the US was normal. MATERIALS AND METHODS: Four hundred prenatal MRI examinations were performed since 1988, and confirmed by postnatal follow-up or pathological examination. Two-thirds of the examinations were performed after 25 weeks of gestation, one-third between 21 and 26 weeks. Fetal immobilisation was obtained by maternal premedication with flunitrazepam, administered orally 1 h before the examination. The examinations were performed on 1.5 T scanners using one or two surface coils. RESULTS: Prenatal MRI allowed the diagnosis of serious unsuspected lesions such as neuronal migration disorders, ischaemic and haemorrhagic lesions and the abnormalities observed in tuberous sclerosis. It helped to characterise ventricular dilatation and anomalies of the corpus callosum and of the posterior fossa. CONCLUSIONS: MRI is a valuable complementary tool when prenatal US is incomplete, doubtful or limited. Prenatal MRI is particularly useful for the detection of ischaemic and haemorrhagic lesions, neuronal migration disorders and tuberous sclerosis lesions. Detection of these associated anomalies worsens the fetal prognosis, has medico-legal implications and modifies obstetric management. Normal prenatal MRI does not exclude an anomaly.

Areas of increased echogenicity in the fetal abdomen: diagnosis and significance.

Areas of increased echogenicity in the fetal abdomen are defined as abnormally bright areas with an echogenicity similar to that of surrounding bones. Such areas are encountered in various normal and abnormal processes. When increased echogenicity is discovered in the fetal abdomen, a careful search should be made for a potential cause. The causes to be considered depend on the location of the areas of increased echogenicity, which can be classified as intestinal, peritoneal, hepatic, retroperitoneal, and parietal. In each case, vascular, ischemic, infectious, tumoral, metabolic, and chromosomal abnormalities should be included in the differential diagnosis before considering the finding a normal variant. Therefore, in utero detection of fetal abdominal areas of increased echogenicity requires a complete sonographic survey of the fetus and placenta along with close sonographic follow-up, evaluation of familial factors, and testing for possible associated cystic fibrosis, infection, or a chromosomal anomaly. The prognosis depends more on the underlying disease than on the extent of the increased echogenicity.