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Chapter 12: Ultrasound Detection of Abnormalities Associated with T18
[Author's note: This chapter was composed in 1993-95,
and was an attempt to compile as complete as list as possible (to my meagre
resources - this was before the Internet took off!) of fetal abnormalities
that were thought up to that time to be associated with Trisomy 18, and to
do a mini-review of each of them. It is not a list and discussion of all
detectable abnormalities, and specifically not of all those associated with
Downs Syndrome. Opinions of the relevance of each of the abnormalities below
vary from "expert" to "expert" (which is exactly to the
point!) and some authors may have have changed those opinions since they published
articles I quote them in here. While the articles presented here may or may
not have become too outdated for practical relevance, they remain of interest
because they were written during the formative years of our fetal ultrasound
paradigms. For that reason alone some of the abnormalities mentioned may be
in need of as thorough an analysis as I have attempted on Choroid Plexus Cysts.
For those fellow non-experts trying to make sense of our scan findings, and
for parents trying to make sense of the findings on their own baby's scans,
please make allowances for these factors. PL Ramm. March, 2004 ]
In this chapter, the fetal abnormalities that have been
associated with T18 are listed and discussed with frequent quotation of
statistics from the more recent and crucial articles. As it will become evident from reading these discussions, similar
controversies to that of CPC are rife in the sonographic community. I have attempted to give both sides of each
argument, when there is such a controversy.
“Soft” signs remain low risk in isolation but when combined
with other abnormalities, the risk increases dramatically. It is worth remembering that chromosomal
abnormalities are present in only 11% of malformed fetuses. Halliday93 recently reported than
in Victoria in 1991, 50% of T18, 42% of T13, and 9.5% of T21 fetuses were
identified by ultrasound examination in women less than 37 years of age (who
therefore did not have routine amniocentesis.)
Awareness of the following “soft” signs should increase these detection
rates.
Several textbooks and review articles have in the early 1990’s
detailed the common ultrasound findings one could expect with T18, particularly
those by Sanders167, Nicolaides133, Eydoux73,
Claussen51, Hegge99, Callen38 and Nyberg139,
and these have been used extensively in the compilation of this section.
12.1 Abnormal Cephalic Index (CI):
The cephalic index is the ratio of the bi-parietal diameter
(BPD) to the occipito-frontal diameter (OFD) and provides an estimation of head
shape. Down syndrome presents with a phenotypic
brachycephaly or short OFD108.
Theoretically, this would produce an increased cephalic index35. However the range of normal CI overlaps that
seen in most cases of Down syndrome, so as an isolated finding this is not
sensitive. Nicolaides133
found an association of 38%, spread over the common aneuploidies, but in fact
most were seen in fetuses with T18 (19/53 cases).
12.2 Strawberry Shaped Head:
According to Smith’s108, a prominent occiput and
a narrow bi-frontal diameter are seen in 50% or more of T18 infants. Nicolaides133 showed the
sonographic equivalent of this sign on the BPD view in 43/83 of fetuses with
T18 and 1/42 with triploidy, termed it “Strawberry head” and gave an
association with aneuploidy of 82%.
Nyberg136 recognised it in 4/29 T18 fetuses between 14 and 24
weeks. This is not a widely reported
finding and it may need to be highlighted to sonographers. In Nicolaides132 series, 10
euploid fetuses with this sign had other abnormalities and only two were born
alive. Other syndromes, such as
Robert’s syndrome may have this head shape.
12.3 Small / Abnormal Cerebellum:
Although Smith’s108 suggests less than 10% of T18
fetuses have cerebellar hypoplasia, Thurmond186 found all five of
her T18 affected fetuses were smaller than expected on measurement of the
transverse cerebellar diameter; Hill103 found 11/19. There is controversy as to whether IUGR
(also seen in T18) affects cerebellar dimension; Reece158 saying it
does not, Hill104 saying it does.
The question arises: is a small cerebellum intrinsic to T18 or a result
of the associated growth retardation?
Partial agenesis of the vermis may be part of a Dandy-Walker variant,
and as such is associated with T18, T13 and T21139.
12.4 Cisterna Magna > 9mm / Dandy -Walker Malformation / Syndrome:
Enlargement of the antero-posterior diameter of the cisterna
magna is presumably related to the cerebellar dysgenesis associated with the
Dandy-Walker variant. A posterior fossa
cyst, representing an enlarged fourth ventricle, of the Dandy-Walker
malformation has also been associated with T18. It was noted by Thurmond186 in her five cases (all in
the third trimester.) Russ164
found two cases of T18 in 15 with the syndrome. Estroff71 found Dandy-Walker variant in 17 fetuses,
five being aneuploid, two of which were T18.
Nyberg137 found 9 cases of enlarged cisterna magna in 47
fetuses with T18, although eight of them had gestational age greater than 24
weeks. Nicolaides133
reported a posterior fossa cyst in 21 cases – eight being T18, six were T13,
three were triploidy, and four were unspecified – but it is impossible to tell
if he is referring to the Dandy-Walker malformation or merely to cisternal
enlargement. Cisternal enlargement
certainly appears to be more evident in the third trimester aneuploid fetus.
12.5 Arnold-Chiari Malformation / Spinal Defects:
The absence of the cisterna magna and a deformed cerebellum
(“banana” cerebellum) (Fig 17) are signs of the Arnold-Chiari
Type II malformation which indicates an open defect of the spinal cord as
found in meningomyeloceles134, 139, (Fig 16). Open spinal defects are occasionally associated
with aneuploidy, but they have been reported in several series. Babcook6 found that 9/52 karyotyped
fetuses with myelomeningocele were aneuploid (5 T18, 2 T13, 1 triploid, 1
translocation) and suggested cytogenetic analysis whenever this anomaly is
found . Nyberg136 found
8/47 spinal defects in fetuses with T18.
According to Sanders167, the risk of recurrence of spina
bifida is lower if there has been a chromosomal association.
Fig 16: Sacral spina
bifida cystica
Fig 17: "Banana" cerebellum and absent cisterna
magna.
12.6 Agenesis of Corpus Callosum:
Often associated with other midline facial and cerebral abnormalities,
such as the holoprosencephaly sequence (hence T13 and T18) and the Dandy-Walker
malformation (hence T18), ACC as an isolated finding is unlikely to be detected
earlier than the third trimester according to Vergagni191. Nicolaides136 series showed three
T18 fetuses to have holoprosencephaly, ergo ACC. Two of Nyberg’s 47 T18 fetuses
had ACC but they were both missed by ultrasound. A variety of other abnormal syndromes may be
associated as well although as an isolated finding it may be a normal variant139. Due to the difficulty of early diagnosis of
ACC with ultrasound, exact data are unknown.
12.7 Cystic Hygroma:
Fluid accumulations around the fetal neck have been
associated with chromosomal abnormalities, particularly Turner’s syndrome, when diagnosed in the
second trimester139.
Recently the use of first trimester transvaginal scanning has increased
the range of findings in the fetal neck187,175. Just what the authors mean when they say
“cystic hygroma” is often difficult to ascertain. The classic findings of cystica hygromata colli, in which
relatively small, circumscribed cystic spaces are present antero-laterally in
the neck at the region of the jugular lymphatic plexus, are rarely seen on the
18-20 week ultrasound, but are seen with greater frequency in the first
trimester190.
In second trimester scans, the term is therefore more
frequently used to describe the extensive posteriorly located effects of
lymphangiectasia (lymphatic vessel dysplasia).
This probably represents early hydropic change and it may extend to the
scalp and the posterior thorax. It may
be associated with generalized hydrops, effusions and ascites. The presence of septations in the cystic
posterior cervical swelling is strongly indicative of chromosomal abnormality31. Brohnshtein29 found aneuploidy in
18/25 (72%) of septated posterior lesions as opposed to 6/106 (5.7%) of
non-septated antero-lateral lesions.
Monosomy X, Turner’s syndrome and T21 are the predominant chromosomal
abnormalities. However, 10/47 of
Nyberg’s136 T18 fetuses had “cystic hygroma.” Euploid conditions which involve lymphatic
dysgenesis, such as Noonan’s syndrome, are missed at karyotyping.
12.8 Nuchal Oedema / Translucency:
Typically identified in the late first trimester, the
presence of a translucent or oedematous region, as distinct from a cystic
loculation, in the subcutaneous tissues at the posterior midline of the neck
and upper thorax of the fetus has been strongly associated with aneuploidy,
particularly T21 and T18, with the incidence of trisomic fetuses ranging from
19% to 88%. In his general series Nicolaides133
found nuchal oedema in 5/83 cases of T18.
In another large study by Nicolaides130 8/33 aneuploid
fetuses with a measurement over 3mm were T18 (total of 88 fetuses). In an elegant autopsy study, Hyett239
demonstrated cardiac defects in 56% of T21 fetuses with nuchal translucency and
suggested that resultant early cardiac failure may be the cause for the finding
rather than lymphatic problems. The
almost universal association of cardiac defects with T18 would point to this as
the cause here also. Pandya149
has suggested a measurement of ³3mm as a suitable cut-off for increased risk for
T21. Nicolaides130 has
suggested a 2.5mm measurement be used as the basis for a first-trimester
screening protocol for T21. Roberts227
however found the sign too insensitive in a low-risk population to be useful
for screening for Downs.
Fig 18: Nuchal translucency in a T21 fetus.
12.9 Hypotelorism:
Hypotelorism (narrow-set eyes) to a variable degree (as far as
cyclopia) is associated with the holoprosencephaly sequence (hence T13 and T18)
and other midline defects. The narrow
bi-frontal diameter in T18 may potentially present as hypotelorism in the
second trimester. Nyberg136
noted it in 3/18 cases of T18, all in the third trimester. We have seen hypotelorism in T21 and T13 in
the second trimester. Hypertelorism
(wide-set eyes) is seen in several abnormal syndromes and in fetuses with
frontal encephaloceles108.
12.10 Facial cleft:
Centrally cleft lip and palate have a high association with
chromosomal abnormalities, particularly T13 and T18166. According to Sanders167, lateral
or bilateral clefts are the more commonly seen, but have less association with
aneuploidy. Most authors are not
specific as to the nature of the cleft (lateral, central, bilateral) which it
makes it difficult to draw an informed conclusion. Benacerraf10 found facial clefts in 5/9 T13
fetuses. Nyberg136 found
clefts in 2/47 with T18. Nicolaides133
found them in 10/83 with T18 and 15/31 with T13 and only 1/69 with T21.
Fig 19: >Unilateral
cleft lip.
12.11 Micrognathia:
Identified on the midline face profile view (Fig.20),
hypoplasia of the mandible is noted in several aneuploidies, particularly T13
and T1810,16, and is generally associated with a poor
prognosis. Bromley27, in a
study of 20 cases of micrognathia, found T18 in 3, T13 in 1 and T9 in 1. Sixteen of these cases died or were
terminated. Nyberg’s136
series of T18 fetuses described only 2/47, while Twining’s188 study
found 5/7. Nicolaides133
found chromosomal abnormalities in 37/56 fetuses with this defect. In his series, 21/83 with T18 had
micrognathia, 3/31 with T13, 9/42 with triploidy and 4 other aneuploidies.
Fig 20: Facial
profile showing moderate degree of micrognathia (receding chin) in a T18 fetus.
12.12 Small Ear:
The normal appearances of fetal ears were first described by
Birnholtz21. He suggested a
possible use of length measurement in predicting aneuploidy, due to the common
association of ear anomalies affecting size, particularly in Down
syndrome. Awwad5 found 3/4
T21 fetuses and 5/6 T18 fetuses to have small ears (below the 20th
centile). Birnoltz21 found
small ears (1.5 SD or more below the mean) in 2/6 T21, 3/3 T13, 3/3 T18 and 1/1
triploidy. Those with T18, T13 and
triploidy showed the greatest deviation from the mean. Lettieri119 found 7/10 T21, 1/1
T18, 1/2 T13, and 1/1 triploidy fetuses
to have small ears. This sign is being
looked at with considerable interest, as it is relatively easy to perform. Gill228 found that while
statistically significant differences from the normal were found in 25
T21fetuses, the results were not clinically useful in individual cases due to
the wide range of normal ear lengths in his study.
12.13 Cardiac Defects / Septal Defects:
Most, if not all T18 babies have a cardiac defect, usually
an atrioventricular or ventricular
septal defect108. However
the ultrasound detection of such defects is not notably successful according to
the literature. Stoll180, in
a large survey performed in Strasburg, found that less than 1.3% of isolated
VSDs were detected, but that this figure rose to 23% when there were other
abnormalities. Equipment quality and
sonographer training have significantly improved since the 1980’s when Stoll’s
survey was carried out. DeVore64
used detailed grey-scale and careful colour Doppler techniques in identifying
aneuploid fetuses in mothers who refuse or are unable to have invasive prenatal
diagnosis with a success of 13/15 (87%) for T21 and 7/7 for T18. Copel57 found 11 (32%) cardiac
defects in 34 aneuploid fetuses.
Conversely, Paladini148 found 15 (48%) aneuploid fetuses in
31 cases of congenital heart disease.
Wladimiroff198 diagnosed cardiac defects (VSD or DORV) in all
23 fetuses with either T13 or T18. All
7 of Twinings188 T18 fetuses had VSDs. Nyberg140 found 14 septal defects (either AV canal
defects or VSDs) in 94 fetuses with T21, although only five (35%) were detected
by ultrasound. In his series of 47 T18
fetuses, 29 had cardiac defects of unspecified nature, 18 (41%) of which were
detected by ultrasound136.
Nicolaides133 showed that 66% of fetuses with heart defect
were aneuploid. About 1/3 of those with
T21 and T18, and one half of those with T13 had cardiac defects
demonstrated.
Careful scanning is required, using techniques which optimize
the image in both grey-scale and colour Doppler. Other cardiac defects noted in T18 are double outlet right
ventricle (DORV) and pulmonary or aortic stenosis. Twining188 reported echogenic foci within the
ventricles in eight of 24 fetuses with choroid plexus cysts. Two of these had
T18, one had T13, and another Turners.
Petrikovsky225 and others have found these foci to be a
normal finding, however Bromley224 noted an increased risk for
T21. We have seen foci in a heart of a
fetus with a VSD and other vascular anomalies, but with normal
chromosomes.
Fig 21: VSD and echogenic
foci in fetal heart. (Normal fetus)
12.14 Renal Anomaly:
A wide of renal anomalies have been associated with
chromosomal abnormalities, from dysplasia and agenesis to mild
pyelectasis. In T18, the commonly
cited anomalies are horseshoe kidney (unlikely to be detected by ultrasound),
cystic and dysplastic kidneys, unilateral agenesis, and a distended and non-visualized
bladder. Nicolaides133 found
renal defects in 25/83 (30%) of cases of T18.
Nyberg136 found renal defects in seven of his 47 cases
(15%). In Nyberg’s series the bladder
was not visualized in two cases (with oligohydramnios in one case, but this may
be related to the concurrence of myelomeningocele) and overly distended in
another. Mild hydronephrosis has been
touted as a fairly strong marker for T21 by Benacerraf15, who uses
it in her and Nadel’s124, 17 scoring system for trisomy. In one series 3.3% of fetuses with
pyelectasis had T21. Corteville58
also found an association, but only 17% of those with T21 had pyelectasis that
they considered too low to warrant its inclusion in a screening test.
Fig 22: Renal
dysplastic change (echogenic, cystic kidney)
12.15 Omphalocele / Exomphalos:
During embryogenesis, a loop of midgut herniates into the
base of the umbilical cord, rotates 90º counter-clockwise, then in the 12th
week (menstrual age), retracts into the abdomen and rotates a further
180º. Omphalocele may be caused by
failure of this retraction, or by failure of the midline ventral wall to close
resulting in a secondary herniation of the gut as well as liver or other organs118. The association with T18 and T13 is high,
particularly early in pregnancy, according to Snijders223. Her extensive literature review demonstrated
chromosomal abnormalities in 149 (31%) of 474 cases. 89 (60%) of the aneuploid cases were T18. In Nicolaides’133 series, 42/116 fetuses
with exomphalos were aneuploid, with 32/83 of the T18 fetuses having this
condition. Gilbert86 found
17 cases of T18 in 35 cases of omphalocele.
Nyberg135 found aneuploidy in 8/8 cases without
liver in the herniation and 2/18 with liver in the herniation. Getachew84 also noted that 4/6
fetuses with gut only in the omphalocele were aneuploid compared to 1/16 when
liver was also present. DeVeciana63
noted absence of liver in the defect, small herniation size and the presence of
other abnormalities to be highly suggestive of T18.
Fig 23: Omphalocele
containing gut only. (Triploid fetus)
12.16 Diaphragmatic Hernia:
Most congenital diaphragmatic hernias (CDH) are of the
Bochdalek type (posterior left defect), which causes pulmonary hypoplasia and
is more usually lethal. Anterior
hernias of Morgagni are less frequent.
Structural or chromosomal abnormalities occur in over 50% of cases
according to Nyberg139.
Benacerraf16 found three cases in 15 fetuses with T18. Comstock52 found one case of T18
in eight CDH. In a large review,
Bollman23 found that 6/33 fetuses were aneuploid, especially
T18. In Nyberg’s136 series,
2/47 T18 fetuses had CDH. In
Nicolaides’133 series, 17/41 fetuses with CDH were aneuploid, with
10/83 of the T18 fetuses having CDH.
Image Unavailable
Fig 24: Diaphragmatic
hernia. Note stomach bubble next to
displaced heart in the thorax.
12.17 “Absent” Stomach (Presumed Oesophageal Atresia [OA]):
A non-visualized stomach relates to oesophageal atresia115,
a frequent malformation in T18. Nyberg136
and Bundy33 have noted this finding. More often than not, however, a tracheo-oesophageal fistula is
present, and fluid can enter the stomach, which may be of normal size, or
slightly smaller, particularly in the 2nd trimester. It may be that increased abdominal pressure in the 3rd trimester
does not allow the filling of the stomach, making this finding more frequent in
later pregnancy, where it is more likely to be related to hydramnios139
(Fig
25). A pouch of distended
oesophagus may be seen in the upper thorax (Fig 26). 17/23 cases of
OA were found to have T18 in Nicolaides’133 series.
Fig 25: Absent (small) stomach with polyhydramnios,
suggestive of OA .
Fig 26: Distended pouch
in upper oesophagus in fetus with OA
12.18 Abnormal Extremities: Introduction
Abnormal extremities, with cardiac defects, are the most
common structural anomalies in T18, yet they are the most poorly identified
with ultrasound. In Nicolaides’133 series, 43% with abnormal
extremities were aneuploid, including 71/83 T18 fetuses. Nyberg136 detected only 50% of
extremity abnormalities. Careful and
methodical scanning is required to assess the extremities. Sonographers should familiarize themselves
extensively with normal anatomy in order to better recognize deviations from
the normal and improve detection in these areas.
12.19 Radial Aplasia / Radial Ray Syndrome (Absent Thumb):
Dramatically shortened or absent
radius with or without shortened or absent thumb (radial ray syndrome) is seen
in 10 - 50% of T18 cases. In Nyberg’s136
series four cases of radial aplasia or radial ray syndrome were missed by
ultrasound. Sepulveda170
detected three cases with T18.
Benacerraf10 noted two radial ray anomalies on 26 fetuses
with T18. Twining188 saw
this in one of his seven cases of T18.
The hand is severely turned towards the radial side of the forearm (Fig
27). This is also seen in a
variety of syndromes such as Robert’s Syndrome or Holt-Oram Syndrome.
Fig 27: Radial
deviation of the hand in a fetus with Holt-Oram Syndrome
12.20 Overlapping Fingers / Clenched Fist (Camptodactyly) / Polydactyly:
Anomalies of the hands are
particularly common in T18. Jones108
states that over 50% have fixed clenched hands and a tendency for overlapping
fingers with the index finger over the third finger and the fifth over the
fourth being the usual configuration.
In T18 these fingers are firmly clenched (camptodactyly) and cannot be
extended. Extension movement of the
fingers therefore excludes this sign.
About 10% of cases may have extra fingers (polydactyly). In Nyberg’s136 T18 series 20/47
had clenched hands. In Benacerraf’s T18
series, 10/ 26 had fisted or clubbed hands.
In Twining’s188 series of seven T18 cases, five had
overlapping fingers, though two only were detected with ultrasound. Polydactyly is a very rare pick-up, but it
is also seen in T13 fetuses. Carlson43
found hand postural deformities, hydramnios and other abnormalities to be
indicative of aneuploidy.
Fig 28: Overlapping fingers in a fetus with
unbalanced translocation T14.
12.21 Talipes / Rockerbottom Feet / Short Hallux:
The most frequent form of talipes is equinovarus, with
plantar flexion and inversion of the foot.
The toes are visible in a row on the same view which shows the long axis
of the tibia, as in Fig:24. Rockerbottom
foot is a posterior subluxation form of talipes (convex pes valgus, or vertical
talus). Viewed from posteriorly, the
heel is prominent as shown in Fig:25. This may be present in 10 -50% of T18 fetuses108. Nyberg136 detected only 1/5 cases
with talipes in his series. 10/26 in
Benacerraf’s T18 series had talipes. In
Twining’s188 series of seven T18 cases, three had rockerbottom feet
or prominent heels. Jones108
described a short, dorsi-flexed big toe in >50% of cases of T18. Sturla Eik-Nes showed such a case at ASUM in
1995† .
Fig 29: Talipes equinovarus (normal fetus)
Fig 30: Prominent heel in rockerbottom
foot anomaly (triploid fetus)
12.22 Hydramnios:
Amniotic fluid (AF) disorders have been reported in many
cases of T18. Oligohydramnios has been
reported, but usually in association with renal dysplasia136. More commonly there is polyhydramnios. Damato61 found chromosomal
abnormalities in seven out of 105 cases (6.7%) of increased AF, one each of
T18, T13, a 4p deletion, and four cases of T21. Brady25 found four chromosomal abnormalities in 125
cases (3.2%) of idiopathic hydramnios: two were T18 (with IUGR) and two were
T21. The paradoxical combination of
IUGR and increased liquor has been noted by Nyberg136 (10/47),
Eydoux73 (7/33) and Claussen51 (2/25). Carlson43, as mentioned, noted
that the combination of hydramnios, hand posturing abnormality and any another
anomalous finding was consistent in 6 trisomic fetuses (27%) of 49 cases of
hydramnios; three with T18, two with T21 and one with T13.
12.23 Intra-Uterine Growth Retardation (IUGR):
A high association of growth retardation with T18 has been
noted; in particular, an association with symmetrical IUGR has been
proposed. 27% of fetuses were “growth
retarded” or small for expected gestational age in the surveyed literature,
although in some individual reports the frequency is 50% or greater (Nicolaides133
48/83, Thorpe-Beeston185 14/17).
This effect is particularly noticeable in those cases which were
diagnosed in the 3rd trimester, although Nyberg136 found a smaller
than expected fetus in eight of 29 cases scanned at 21 weeks or less. IUGR with increased or normal liquor is also
an unexpected and common finding in all chromosomal abnormalities. Absent or reversed end-diastolic flow in the
umbilical artery has a very high correlation with IUGR. Rizzo160 evaluated the karyotype
of 192 fetuses with absent end-diastolic flow on umbilical artery Doppler,
known to be associated with placental failure, severe growth restriction and
poor fetal outcome. 16 (8.3%) of these
fetuses were aneuploid; nine T18, four T21 and one 14p deletion. The supposed association of symmetrical
growth retardation was not evident in Rizzo’s study, nor in Snijders176,
where HC/AC ratios were also increased without any significant difference from
the HC/AC ratios in their chromosomally normal but growth retarded
fetuses. Snijders176 found
no increase in Doppler abnormalities to explain her findings however.
12.24 Two Vessel Cord (Single Umbilical Artery, SUA):
Parilla229 studied 50 cases of isolated SUA and
found none with chromosomal abnormality.
Nyberg136 however found it in 9/47 T18 fetuses. Saller165 found six SUA in 53
aneuploid fetuses; two were T18, two were T13, and the other two were unusual
translocations. In another study Nyberg138
found that 12/30 fetuses with SUA had other major abnormalities and six of
these were aneuploid. Hence the
presence of other abnormalities is crucial in determining the significance of
this finding (similar to CPC). There is
an association with IUGR and post-natal renal reflux noted by Sepulveda169. Detection is quite difficult in obese
patients, and Jones109 suggests that only 65% are detected
overall. Using colour flow to assess blood-flow
in the umbilical arteries around both sides of the bladder is probably the best
diagnostic technique when clear images of the cord in the amniotic fluid cannot
be obtained. Jeanty107 noted
that the lower abdominal aorta at the bifurcation curves way from the side on
which the artery is absent, and that the iliac artery is smaller.
Fig 31: Single umbilical
artery (otherwise normal fetus).
12.25 Allantoic / Cord Cysts:
Nyberg136 saw 2 cases of allantoic cysts (remnants
of the funicular diverticulum of the urogenital sinus) in his T18 series,
but these were associated with omphaloceles, which corresponds with the earlier
findings of Fink76. It
may be that their association is with omphalocele rather than with chromosomal
abnormality independently. Jauniaux230
reported on two cases of “pseudocysts” in the cords of T18 fetuses.
Hegge99 described multiple cord cysts in a case of T18.
12.26 Signs of Other Chromosomal Abnormalities:
The abnormalities discussed above while not specific to T18
are commonly associated with it. The
following abnormalities have also been detected on ultrasound in association
with chromosomal abnormalities, particularly T21. They are referenced to the bibliography, but not discussed in
detail.
Shortened Fronto-thalamic Distance.7
Thickened Nuchal Fold (>6mm at 18 weeks) 9, 11, 151
Ventriculomegaly. 17,18,124,133,140,167,
Holoprosencephaly. 167,10,16,38
Open Mouth, Protruding Tongue. 99,133
Renal Dilatation. 58,15,17,18,124,220
Duodenal Atresia. 99,38,133,140,
Echogenic Bowel. 140,220,124,168,28
Ascites / Hydrops. 133,140
Lengthened Iliac Wing Distance. 1
Shortened Humerus. 162,32,19,161
Hitchhiker’s Thumb. 43,
Hypoplasia 5th finger, Middle Phalanx. 13,20
Shortened 5th finger. 13,20
Inward Curving 5th Finger (Clinodactyly). 99
Shortened Femur. 220,17,18,
Wide-spaced 1st and 2nd toes (Sandal Gap). 167
These soft signs complete the list devised for the
Chromosomal Pro-Forma discussed in
Chapter 15.
12.27 Conclusion:
The search for other abnormalities is the crucial part of an
ultrasound examination of a fetus with CPC.
While all areas should be examined in detail, looking for the markers
discussed above, it is by the careful evaluation of the cranial shape and
contents, and the face, correct scanning of the heart and detailed assessment
of the extremities that the subtle yet common findings in T18 will be
uncovered. Some findings are more
easily detected or more prominent in the third trimester. Examples of such findings are IUGR, agenesis
of the corpus callosum, amniotic fluid disorders, cisterna magna enlargement
and cardiac defects. Attention to
technique and a use of good machine can only allow the anatomy to be displayed
on the screen. In order for this to be
of any use, the sonographer must firstly recognize abnormalities. It must be stressed that detailed scanning
of normal fetuses during the 18 - 20 weeks scan is strongly recommended,
within the constraints of available time and image quality, so that
sonographers become extremely familiar with fetal structures in their normal
anatomical configurations. Only when
knowledge, experience and scanning skill are united in the well-trained
sonographer will most abnormalities be recognized, and a presumptive diagnosis
of chromosomal abnormality suggested, guiding the management of these at-risk
pregnancies.
When abnormal findings are seen to place the fetus in this
at-risk category, genetic counseling and analysis of risk may indicate the need
for amniocentesis. These matters are
discussed fully in the following chapters.