Trisomy 9 presenting in the first trimester as a fetal lateral neck cyst and increased nuchal translucency

Abstract

Background Fetal lateral neck cysts are transient fluid accumulations that result from abnormal lymphatic formations. In the first trimester, fetal lateral neck cysts accompanied by an increased nuchal translucency have been associated with aneuploidy, single-gene disorders and other malformations. Highlights We describe a case in which a lateral neck cyst, which measured 6.7 × 4 × 6.2 mm, was detected by ultrasonography in the first trimester with the additional finding of increased nuchal translucency (3.7 mm; >95th percentile). No other abnormalities were detected at that time. Standard cell-free DNA screening resulted in no aneuploidy detected for chromosomes 21, 18, 13 and the sex chromosomes. The patient declined diagnostic testing with chorionic villus sampling. A repeat ultrasound at 16 weeks’ gestation demonstrated a normally grown fetus with persistence of the cyst, which measured 4.9 × 5 × 8.4 mm, as well as a pericardial effusion with a single outflow tract overriding the ventricular septum and vermian hypoplasia. The diagnosis of trisomy 9, 47,XX,+9, was made by amniocentesis and the patient opted for termination of the pregnancy. Conclusions This report illustrates the importance of identifying additional abnormalities in a fetus with lateral neck cysts, documenting the size of the cysts and obtaining diagnostic genetic testing.