ultrasound diagnosis of fatal anomalies

TRISOMY 21
Fig. 9.56 Trisomy 21. Nuchal translucency at
17 + 6 weeks.
achieved in 60%. Using a combination of maternal
age, measurement of nuchal translucency
(11–13 weeks) and determination of PAPP-A and
free -HCG in maternal serum, diagnosis can be
achieved in 90% (cut-off level 1 : 350).
Teratogens: Not known.
Etiology: Chromosome 21 is found twice in the
ovum or the sperm, as a result of incorrect division
during germ-cell development (meiotic
nondisjunction). This process of meiotic nondisjunction
occurs in 95% of cases in maternal
germ-cell development; the paternal germ cells
are responsible in only 5% of cases.
Ultrasound findings: Nuchal translucency
screening at 11–13 weeks detects a thickening of
the nuchal fold in 70–80% of affected fetuses. The
upper limit for this measurement (mostly
2.5 mm) depends on the maternal age and
fetal crown–rump length. A nuchal fold
measurement of above 6 mm at about 18 weeks
of gestation may also be suspicious for Down
syndrome, but the sensitivity is low at this gestational
age. Other ultrasound findings are: nonimmune
fetal hydrops, isolated hydrothorax, mild
ventriculomegaly, brachycephaly, flat facial profile
with a small nose, urethral valve syndrome
with megacystis, intestines with a strong echo
(the echo from the small bowel resembles that
from the bones), duodenal stenosis (“double
bubble”, seen after 24 weeks), omphalocele,
mild dilation of the renal pelvis ( 4–5 mm at
21 weeks), clinodactyly, hypoplasia of the
middle phalanx of the fifth finger (difficult to reproduce),
short femur and humerus (frequently
false-positive), general growth restriction, sandal
gap between the big and the second toes. In
40–50% of cases, cardiac anomalies such as AV
canal, membranous inlet VSD, hypoplasia of the
left heart, and tetralogy of Fallot.
Differential diagnosis: Depending on the ultrasound
findings, various syndromes can be considered,
for example: Cornelia de Lange syndrome,
Noonan syndrome, Roberts syndrome,
Smith–Lemli–Opitz syndrome, hypoplasia of the
Fig. 9.57 Trisomy 21. Slightly abnormal facial profile
at 23 weeks, with flattening of the nose.
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