Trisomy 18

(A) Axial scan through the fetal head at 21 weeks of gestation showing a strawberry-shaped skull (flat occiput and pointed frontal bones) in a fetus with trisomy 18. This is a non-specific marker for trisomy 18. Note the prominent cavum septi pellucidi ("+") and the choroid plexus cyst (arrow). This fetus had numerous other congenital malformations, including Tetralogy of Fallot, that led to the sonographic suspicion of trisomy 18.
(B) Overlapping index finger (arrowhead) in a persistently clenched hand.
(C) Foot with prominent heel (thick arrow).
(D) Three-dimensional ultrasound surface rendering of a fetus with trisomy 18 showing micrognathia, low-set ears, and a clenched hand, which was persistent.
(E, F) Upper extremities of a fetus with trisomy 18 and bilateral radial ray defects (arrow) at 24 weeks of gestation. This fetus also had a tetralogy of Fallot.