Cerebral lateral ventricular asymmetry: is this a normal ultrasonographic finding in the fetal brain?

OBJECTIVE: To evaluate the clinical significance of in utero detection of fetal cerebral lateral ventricular asymmetry.
METHODS: We used high resolution ultrasonography to study asymmetries of the fetal lateral ventricles in the human brain. A retrospective survey was conducted on 7200 pregnant women who presented at two large district hospitals in Israel. Only fetuses with a difference of greater than 2.4 mm (two standard deviations) in the width of the lateral ventricles, with no known brain pathology, were included in the study. Index cases were evaluated regarding maternal complications, prenatal ultrasound examinations, postnatal imaging studies, and neonatal outcome up to 6 months of age.
RESULTS: Lateral ventricular asymmetry was found in 21 subjects, all with available clinical data. In 15 fetuses (71%), the body or the occipital horn of the left lateral ventricle was larger than the right, whereas in six fetuses (29%), the right was larger than the left. In four cases (20%), serial scans noted resolution of asymmetry; in 15 (75%), it was persistent; and in one (5%), asymmetry increased. In one case, termination of pregnancy was performed; however, pathologic examination of the fetal brain failed to detect any structural abnormality. Underlying cerebral pathology was later found only in three fetuses (14%); one had subclinical cytomegalovirus ventriculitis, one had insidious periventricular hemorrhage, and in one fetus with increased asymmetry, trisomy 21 was verified. All the remaining 17 cases had normal neurologic development.
CONCLUSIONS: Some degree of asymmetry of the lateral ventricles exists in the human fetal brain and is detectable in utero. Lateral ventricular asymmetry alone is probably not clinically significant, and it may be considered as a normal variant, rather than a pathologic finding.