The ventricular atria in 100 healthy fetuses with gestational ages ranging from 14 to 38 menstrual weeks were evaluated and compared with those of 38 fetuses in whom ventriculomegaly had been diagnosed in utero. Axial sonograms of the brain through the atrium of the lateral ventricle demonstrated that the normal atrial diameter remained relatively constant throughout the gestational age range observed. The atrium had a mean diameter of 7.6 +/- 0.6 mm (standard deviation [SD]). Measurement of this structure can be quickly performed, is reproducible with low intra- and interobserver variation, and permits ventriculomegaly to be excluded. Atrial diameters exceeding 10 mm (above 4 SDs) suggest ventriculomegaly, with a low false-positive rate.
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.
The medical records of 55 fetuses with sonographically diagnosed mild ventriculomegaly (MVM) were reviewed to assess prognosis. Fetuses were divided into two groups based on the presence or absence of sonographically detected associated fetal anomalies: 13 had no other anomalies detected (isolated MVM), and 42 had concomitant neural axis and visceral anomalies (nonisolated MVM). Mortality was 83% among fetuses with nonisolated MVM and 38% among fetuses with isolated MVM (P less than .005). If terminated pregnancies are excluded, only one of nine (11%) fetuses with isolated MVM died, compared with nine of 16 (56%) fetuses with nonisolated MVM (P less than .005). There are 15 living children: Nine (60%) are developmentally normal at 6-30 months of follow-up (six had isolated MVM), three (20%) are or are likely to be abnormal, and we were unable to follow up three (20%). Fetal anomalies were missed in 11 of 30 (37%) fetuses with detailed follow-up. However, this would have changed the classification from isolated to nonisolated MVM in only one case. Thus, in 54 of 55 cases (or 29 of 30 cases with detailed follow-up), fetuses were accurately classified as having isolated or nonisolated MVM. The authors conclude that sonographically isolated MVM is associated with a significantly better prognosis than nonisolated MVM, and fetuses can be classified accurately based on prenatal sonograms.
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