Diagnostic ultrasound ( PDFDrive )

CHAPTER 31 Chromosomal Abnormalities 1103
FPR with no signiicant change in detection rate of Down
syndrome. 172,173 It has been cautioned that the use of genetic
sonography ater irst-trimester risk assessment may result in
increased patient anxiety without increasing the detection rate
of trisomy or false reassurance. 173,174 While historically the inding
of an isolated marker would potentially result in a diagnostic
test that came with an associated risk of fetal loss, the recent
incorporation of cell-free DNA provides a secondary level of
screening that does not carry a risk of pregnancy loss. A negative
cell-free DNA analysis makes the identiication of a marker of
unlikely clinical importance with respect to aneuploidy screening.
175 Certain markers such as short femur, echogenic bowel,
or urinary tract dilation may be associated with other concerning
clinical situations.
TRISOMY 18 (EDWARDS SYNDROME)
Trisomy 18 is the second most common autosomal trisomy, with
a prevalence of 4.8 per 10,000 total births. 176 With improving
prenatal diagnosis and associated high termination rates, the
live birth prevalence has decreased to 0.1 in 1000. 177 Individuals
with this disorder have a limited capacity for survival, with 44%
of those identiied in utero dying before birth. 178 About 50% of
afected newborns die within the irst week, and only 5% to 10%
survive beyond the irst year of life. hose who survive are severely
intellectually disabled and physically handicapped. 179
Fetuses with trisomy 18 have a plethora of anomalies. Sonographically,
77% to 97% of fetuses with trisomy 18 can be identiied
by the presence of these structural malformations. 180-184 he more
common structural anomalies in fetuses with trisomy 18 include
congenital heart defects, central nervous system anomalies,
hydrocephalus, diaphragmatic hernia, omphalocele (70% of
which only contain bowel), and abnormally clenched hands
(with overlapping index ingers) 180-184 (Fig. 31.11). In our experience,
cases of trisomy 18 not identiied by prenatal ultrasound
have been scanned early in the second trimester, when a complete
structural survey was not feasible or when other factors such as
surgical scarring or maternal body habitus precluded optimal
visualization of the fetus. 157,158
Trisomy 18: Common Sonographic Findings
Choroid plexus cyst
Strawberry-shaped skull
Abnormal cerebellum, cisterna magna
Neural tube defects
Cardiac defects
Omphalocele
Esophageal atresia
Diaphragmatic hernia
Clenched hands, overlapping index ingers
Radial ray anomalies, limb reduction defects
Clubfeet, rocker-bottom feet
Intrauterine growth restriction (especially with
polyhydramnios)
A
B
C
D E F
FIG. 31.11 Second-Trimester Sonographic Findings in Trisomy 18. (A) Choroid plexus cyst. Scan through the fetal head at 18 weeks
shows bilateral choroid plexus cysts. (B) Omphalocele. Scan of the fetal lower abdomen shows a bowel-containing omphalocele (arrow) as well
as an umbilical cord cyst. (C) Clenched ists. Three-dimensional scan of a midtrimester fetus shows characteristic clenching of the hands and
overlapping ingers. (D) Radial ray anomaly. Three-dimensional scan demonstrates a radial ray anomaly. Note the micrognathia as well. (E)
Strawberry-shaped skull. (F) Three-dimensional scan of the fetal spine at 18 weeks demonstrating a neural tube defect (arrow).