A choroid plexus cyst, in the absence of an associated anom­aly, should be considered a normal anatomic variant. Parents are often concerned about having “cysts in the brain,” but they should be reassured that these are usually normal and decrease rapidly in size by the third trimester. Only rarely are any remnants of the cyst identied after birth. Although cho­roid plexus cysts are benign, this transient nding is associated with increased risk of trisomy 18. Trisomy 18 is also known as trisomy E or Edwards syndrome. With the detection of a choroid plexus cyst, the patient’s age and biochemical marker values should be reviewed. In addition, a targeted ultrasound examination should be performed to check for potential abnormalities associated with trisomy 18. This genetic syn­drome is associated with numerous ndings, including cho­roid plexus cysts, strawberry-shaped head, small low-set ears, a single umbilical artery, umbilical cord cyst, intrauterine growth restriction, clubbed or rocker-bottom feet (Figure B), and clenched hands (Figure C). Structural abnormalities are often present in fetuses with trisomy 18, including central nervous system ndings such as spinal bida, hydrocephalus, or an abnormal posterior fossa. In one series, there was associated mild increased risk of alobar holoprosencephaly, although this is rare. Heart anomalies also are often detected in fetuses with trisomy 18, including ventricular septal defect and atrioven­tricular canal and complex cardiac malformations (Figure D). Other ndings include omphalocele and genitourinary abnor­malities such as hydronephrosis.