Ultrasonography of the fetal neck in the first and second trimesters. Part 2. Anomalies of the posterior nuchal region.

Over a 5-year period, the author examined the posterior nuchal region of the fetus in 7200 first- and second-trimester sonograms. Nuchal fluid collections were analysed to differentiate physiologic collections, which resolve spontaneously, from pathologic ones, which necessitate invasive testing for chromosomal abnormalities. Recommendations for evaluating ultrasonographic findings, based on the results of the study, are presented algorithmically in this pictorial essay. A single echogenic line representing a skin reflection was usually visible in normal fetuses. Thin double echogenic lines, observed in eight cases in this series, were due to fetal rotation or the presence of an amniotic membrane adjacent to the normal dorsal pseudomembrane and were not indicative of abnormality. In three cases the spectral reflection of the fetal neck surface was relatively thick, leading to the appearance of thick double echogenic lines; of these, two cases involved Down's syndrome. Therefore, karyotyping is suggested in all cases of thick echogenic lines. Of the 11 nuchal fluid collections up to 5 mm in diameter observed in this series, 10 resolved spontaneously by 24 weeks gestational age. In the other case the collection enlarged, and karyotyping revealed Turner's syndrome. Of the 16 cases of nuchal fluid collections greater than 5 mm in diameter, 5 were associated with an abnormal karyotype (Down's syndrome in 4); karyotyping is recommended in all such cases. Nuchal edema occurred in 22 cases. It was associated with Down's syndrome in 8 cases and with trisomy 18 in 1 case. Among fetuses with nuchal edema, the frequency of aneuploidy was substantially greater if other abnormalities were also present.(ABSTRACT TRUNCATED AT 250 WORDS)