Diagnostic ultrasound ( PDFDrive )

1104 PART IV Obstetric and Fetal Sonography
he sonographic indings observed in fetuses with trisomy
18 vary with gestational age. As expected, anomalies such as
cystic hygromas are seen more frequently in the late irst and
early second trimester, whereas cardiac defects and growth
restriction tend to be later indings. In a review of 47 fetuses
with trisomy 18, Nyberg et al. 183 identiied cardiac defects
in 14% before 24 weeks’ gestation and in 78% scanned ater
24 weeks. Intrauterine growth restriction (IUGR) was seen
in 28% of afected fetuses scanned at less than 24 weeks and
in 89% of those evaluated in the third trimester. IUGR, in
combination with polyhydramnios, is an ominous observation
highly predictive of trisomy 18. 183,185 In addition to
those mentioned earlier, other indings, such as radial ray
defects, rocker-bottom feet, clubfeet, strawberry-shaped skull
(lattening of occiput with pointing of frontal bones), and
abnormal-appearing cerebellum and cisterna magna, have been
reported. 179-190
Choroid Plexus Cysts
Choroid plexus cysts (CPCs) are discrete echolucencies within
the choroid plexus that result from the folding of the neuroepithelium,
trapping secretory products and desquamated cells 191
(Fig. 31.11A). CPCs are seen in 1% to 2% of the normal fetuses
and are most common in the second trimester, usually resolving
by 28 weeks’ gestation. 180-182 About 30% of fetuses with trisomy
18 have CPCs. 182,183 he majority of fetuses with trisomy 18 also
have other structural anomalies to suggest aneuploidy. 180-183
Cyst number, size, and laterality are not useful in distinguishing
afected fetuses from normal fetuses. 192-194 Additionally,
resolution of CPCs does not necessarily relect a normal
karyotype. 195
he predictive value of isolated CPCs for aneuploidy is low
when no other abnormalities are seen. 155,182 herefore ater a
CPC is seen, a detailed ultrasound assessment of the fetus should
be performed. In the setting of an isolated CPC, correlation with
a priori risk of trisomy 18 based on an accepted screening protocol
is recommended. 155,196 Cheng et al. 197 reported on the signiicance
of isolated CPCs in a population previously screened with NT
and found that the likelihood ratio for trisomy 18 was not
increased in those with normal NT measurements. Noninvasive
prenatal screening with cell-free DNA can be considered. Invasive
testing is not warranted in the setting of an isolated
CPC. 185,193,194,198-202
TRISOMY 13 (PATAU SYNDROME)
Trisomy 13 is the third most common autosomal trisomy with
a prevalence of 1.9 in 10,000 total births. 176 With improving
prenatal diagnosis and associated high termination rates, the
live birth prevalence has decreased to 0.03 in 1000. 177 Individuals
with trisomy 13 have numerous structural abnormalities and are
severely intellectually disabled. Anomalies oten seen include
forebrain defects, ocular malformations, facial clets, heart defects,
and abnormal extremities. In fetuses that are not terminated,
there is a 46% intrauterine fetal death rate and 93% early
neonatal mortality rate. 203 Rarely, survival is more long term. 204
Sonographic detection of fetuses with trisomy 13 is 90% to 100%
(Fig. 31.12). 157,158,205-209
Trisomy 13: Common Sonographic Findings
Holoprosencephaly
Microcephaly
Neural tube defects
Facial clefts, ocular anomalies
Cardiac defects
Echogenic intracardiac focus
Congenital diaphragmatic hernia
Omphalocele
Echogenic kidneys
Postaxial polydactyly
Intrauterine growth restriction
Cardiac and central nervous system defects are the most
frequently identiied anomalies. he most common central
nervous system malformations identiied in trisomy 13 are
holoprosencephaly, ventriculomegaly, microcephaly, and
posterior fossa malformations. Alobar holoprosencephaly is
oten associated with severe midline facial defects, including
hypotelorism, microphthalmia, anophthalmia, cyclopia, and
proboscis. In addition, fetuses with trisomy 13 oten have postaxial
polydactyly, abnormal hand coniguration, echogenic kidneys,
atypical calciications, and IUGR. 205-209
TRIPLOIDY
Triploidy is the result of a complete extra set of chromosomes (69
chromosomes) and is not related to maternal age. 210 he extra set
of chromosomes may be paternally derived (diandric), usually
from a double fertilization, or maternally derived (digynic) from
fertilization of a diploid egg. 211 he frequency of the parental origin
has been widely disparate with diandric cases in 20% to 85%. 212
Triploidy occurs in 1% to 3% of conceptions, and most are spontaneously
aborted. 213,214 he prevalence of triploidy at 11 to 14 weeks
is 1 in 6614 and survival of a fetus with triploidy beyond 20 weeks’
gestation is unusual. 48,210 Paternal triploid origin is oten associated
with a large placenta illed with cystic spaces and moderate growth
restriction. Triploidy on the basis of an extra maternal chromosomal
complement is usually associated with a small placenta and asymmetric
IUGR. 211,213 Fetuses with triploidy have a multitude of
structural malformations, most oten involving the central nervous
system, heart, and hands 214,215 (Fig. 31.13).
Triploidy: Common Sonographic Findings
Neural tube defects
Ventriculomegaly
Posterior fossa anomalies
Micrognathia
Cardiac anomalies
Omphalocele
Renal anomalies
Talipes equinovarus
3-4 Syndactyly
Asymmetric growth restriction
Abnormal placenta (hydropic changes or small)
Oligohydramnios