Detection of fetal central nervous system anomalies: a practical level of effort for a routine sonogram.

Abstract

To evaluate the efficacy of examining the lateral ventricular atrium, cisterna magna, and cavum septi pellucidi as a means of ascertaining that the development of the fetal central nervous system (CNS) is normal, a retrospective evaluation of the sonograms of 112 fetuses (15-39 weeks gestational age) with sonographically diagnosed CNS anomalies was performed. Malformations included in the study were diverse. The lateral ventricular atrium was enlarged (greater than 10 mm) in 99 (88%) fetuses. Of the remaining 13 fetuses, seven had an abnormal-sized cisterna magna (less than 2 mm or greater than 11 mm). These two measurements alone could be used to identify the presence of a CNS abnormality in 95%. Three of the six remaining fetuses exhibited gross abnormalities easily seen on the standard axial images obtained for biparietal diameter measurement. Although the cavum septi pellucidi was absent in a number of cases, its absence did not enhance sensitivity in the cohort examined. Prospective examination of 130 consecutive normal fetuses (15-40 weeks gestational age) was also performed. When specifically sought, the ventricular atrium was identifiable and measurable 99% of the time; the cisterna magna, 90% of the time; and the cavum septi pellucidi, 95% of the time. Because major CNS anomalies are uncommon and these measurements afford high sensitivity, an extremely low probability (0.005%) of abnormal brain or spinal cord development can be predicted if a normal-sized lateral ventricular atrium and cisterna magna are present. These results should not be construed as a license to underexamine fetuses for malformations. Rather, these measurements should serve as simple positive steps to assist in a difficult task.

Prenatal diagnosis of lipomyelomeningocele.

“…Almost all open neural tube defects are associated with an abnormal appearance of the posterior fossa on obstetric sonographic examination. 7 In this case, the posterior fossa was completely normal. Spinal dysraphism is classified into open (spina bifida aperta) and closed (spina bifida occulta) forms.…”

A Prospective Study of Fetuses with Isolated Ventriculomegaly Investigated by Antenatal Sonography and In Utero MR Imaging

“…8 Fetal VM is associated with poor outcome in terms of both mortality and morbidity if projected outcome data from termination of pregnancy cases are included. 9 Once VM has been demonstrated on a screening sonography examination, women are referred to specialist fetal/maternal centers for further sonographic assessment, which includes detailed neurosonography by an expert in fetal imaging.…”

Three-dimensional neurosonography — a novel field in fetal medicine

“…Measurement of cisterna magna between 2-11 mm and atrial width of the lateral ventricles < 10 mm have very high negative, predictive value for the detection of brain abnormalities [13,14]. Using those two criteria, the majority of CNS defects may be excluded.…”