Trisomy 18 : What are the common association with Trisomy 18 which may be a common or an uncommon association but not impossible: CPSs can be a significant finding because there have been reports in the literature over the years describing the association of CPSc with fetal aneuploidy specifically with trisomy 18 .CPCs appear to be present in approximately one third of trisomy 18 fetuses.
Because of this association there is
much debates to whether fetuses having CPCs
on ultrasound should undergo karyotyping It is clearly recommended that
when fetuses with CPCs have
other sonographic finding invasive testing should be offered. However when
prenatal sonography by experienced personnel reveals that the CPCs are isolated management should be conservative. However some investigators believe that fetuses
having isolated CPCs and no other anomalies may still carry a risk of aneuploidy
high enough to justify
amniocentesis. However the critical
component lies in whether an isolated CPC is in fact truly isolated. This can only be presumed once a detailed fetal survey by experienced examiners has
failed to reveal other structural abnormalities /markers .Therefore it is imperative
that all fetuses with CPCs
undergo a detailed fetal sonographic
anatomic survey by someone who is skilled and expe4rienced
in prenatal diagnosis.
Part
II: Whhat are the abnormalities associated with Trisomy
18
Association with
Trisomy 18:- In trisomy 18 growth is usually restricted . CNS abnormalities associated with Edward syndrome are A) choroid plexus
cyst B) abnormal cisterna magna C) absent corpus callosum D) cerebella hypoplasia E) ventriculomegaly G) strawberry shaped
calvarium and F) neural tube defects.
Quite often, there are few skeletal abnormalities . Skeletal abnormalities include limb reduction defects, overlapping index
finger, clubbed feet,, rocker bottom feet
and polydactyl.
Facial defects are also sometimes seen like cleft lip and palate , micrognathia, low set ears and microphthalmos.
Cardiovascular
abnormalities in Trisomy 21 : May be associated with this syndrome are omphalocele
, diaphragmatic hernia, hydronephrosis
and horseshoe kidney .
Umbilical cord cysts and double vessels umbilical cord may also be observed.
Several meta analyses have been
reported in the literature with regard to fetuses with isolated CPCs .
One report revealed
that had a 0.27 %
incidence of trisomy 18 and five had Down syndrome. Their study suggested a likelihood ratio of 13 .8 for trisomy 18 and 1.87 for Down syndrome contains a summary of reported studies examining the
incidence of aneuploidy in fetuses with isolated CPCs
The majority had no cases of
aneuploidy whereas eight studies found an association of isolated CPCs
with chromosomal anomalies.
Snijders et al found CPCs in 505 of
their fetuses with trisomy 18 and in
1% of chromosomally normal fetuses.
However because the vast majority of affected
fetuses showed other
sonographic anomalies the risk
of isolated CPCs was only marginally increased with a likelihood ratio less than 2 however
the presence of just one other abnormality increased in the risk 20 times. Recently we
examined the prenatal sonographic features
of 38 fetuses with trisomy 18 and found that 50% had CPC
identified but they were always associated
with multiple other
sonographic abnormalities Recently
De vore also found the prevalence of CPCs in trisomy 18
fetuses to be 53% and when
these cysts were isolated they
were not associated with trisomy 18. In anther study by our group
we found that of 98 fetuses with isolated CPCs no one
had aneuploidy whereas of the 13
fetuses with CPCs non had
aneuploidy whereas of he 13 fetuses with CPCs and major anatomic abnormalities 100%
had trisomy 18. Subsequently one
group of investigators found that all 131
fetuses with isolated CPC had normal karyotypes and all fetuses with
aneuploidy had additional abnormalies.
In addition we have shown that
from a cost benefit point of view invasive testing based on the presence of
isolated CPCs is not
justified.
Previously it has also been believed
that large cysts or bilateral cysts increased the risk for aneuploidy some evidence suggests that these larger cysts
further increase the risk for trisomy 18
. However this should still be
regarded within the context of whether
other abnormalities’ are also present or
not . Although CPCs always resolve larger cysts may take longer to undergo this process lending support to
the observation that delayed resolution of CPCs may carry an increased risk for
trisomy 18 .
One
must also remember that it has
been shown that small unilateral
lesions may be seen in chromosomally abnormal fetuses. Whether CPCs are
unilateral or bilateral is probably not
significant although it is probably the case
that larger cysts also tend to be
bilateral . In our study of he 19
trisomy 18 fetuses with
CPCs 79% had bilateral cysts of
these six had a moth eaten
appearance of the choroid plexus. On the other hand four fetuses had unilateral
CPCs of whom three had only a single
cyst.
Unlike for trisomy 18 a possible relationship
between CPC and trisomy 21 is
somewhat controversial Some studies have suggested that CPCs
are associated with Down syndrome
in the second trimester . However
Bromely showed that the incidence
of CPCs in the normal population was the same as the incidence of cysts among fetuses with Down syndrome .
Thus they concluded that the presence
of CPCs did not increase a
patient’s risk for fetal
Down syndrome In a meta
analysis he authors reported that
isolated CPCs were associated with a fetal
Down syndrome risk of 1/880
which is the same as that of the general population.
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