Fetal Aneuploidies

and Marcelo Zugaib4



(1)
São Paulo University, Bauru, Brazil

(2)
Parisian University, Bauru, France

(3)
Member of International Fetal Medicine and Surgery Society, Bauru, Brazil

(4)
Obstetrics, University of São Paulo, Bauru, Brazil

 



The most common prenatally diagnosed aneuploidies are the trisomies of chromosome 21 (Down syndrome), 18 (Edwards syndrome), 13 (Patau syndrome), and Turner syndrome. Other aneuploidies also detected by cytogenetic studies include abnormalities in the number of sex chromosomes (besides Turner syndrome), triploidy, deletions, and translocations. The incidence of aneuploidies increases according to maternal age, except in cases of sex chromosome aneuploidies. In general, the prevalence of aneuploidies is stable in relation to maternal and gestational age. The approximate frequencies are 0.5% in women at 35 years, 1.2% at 37 years, 6% at 43 years, and 15% at 45 years.

In many countries, fetal aneuploidy screening programs are applied and invasive procedures are usually offered to pregnant women over 35 years of age (WHO definition of advanced maternal age). Above 35 years, the incidence of abnormal fetal karyotype exceeds the risk of fetal loss inherent to invasive diagnostic procedures.

In the last few years, even after the spread of diagnostic methods, the number of fetuses born with syndromes, especially Down syndrome, has not decreased. This is because 70% of the children with aneuploidies are born from a low-risk pregnancies group (under 35 years).

The ultrasound findings can determine an increased risk for chromosomal abnormalities in a patient who would not have an indication for fetal cytogenetic study based on age only; moreover, women with advanced maternal age who decline to perform invasive tests may have their risk decreased after screening. This helps when they choose not to obtain a certain diagnosis by undergoing an invasive procedure.


17.1 Trisomy 13


Trisomy 13 normally presents with several ultrasound abnormalities (the rare cases of mosaic trisomy 13 are exceptions). The most suggestive findings are: holoprosencephaly, microcephaly, hypotelorism, sloping forehead, cyclopia, cleft lip and palate, structural heart disease, diaphragmatic hernia, omphalocele, growth restriction, dysplastic kidneys (hyperechogenic kidneys with increased volume), hypospadias, cryptorchidism, polydactyly, and a single umbilical artery.

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Fig. 17.1
Transverse section of the fetal head showing a “strawberry”-shaped skull in a case of trisomy 18 (Tri 18)


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Fig. 17.2
Similar fetal head section in another case of trisomy 18 showing the abnormally depressed temporal bones (arrows), which confers the typical “strawberry”-shaped skull. T = thalamus


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Fig. 17.3
Another case of trisomy 18 with “strawberry”-shaped skull at a higher magnification and advanced gestational age (35 weeks and 3 days)


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Fig. 17.4
Fetal face profile from the same case as in Fig. 17.4 with typical trisomy 18 features: prominent forehead, flat nasal bridge, and micrognathia


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Fig. 17.5
Typical fetal face profile of trisomy 18 with an unbalanced facial portion. The forehead portion predominates (caliper 1) over the middle third (caliper 2) and the lower third (caliper 3), which extends from the nasal philtrum to the chin


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Fig. 17.6
Trisomy 18 fetal profile. Predominance of the forehead, also called high or prominent forehead


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Fig. 17.7
Oblique coronal section of the fetal brain showing a bilateral choroid plexus cyst in a case of trisomy 18. Choroid plexus cysts are normal findings until 22 weeks of gestation and, when isolated, are not indications for fetal chromosomal analysis


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Fig. 17.8
Transverse section of the fetal head at the level of the ocular orbits showing bilateral microphthalmia (arrows) in a case of trisomy 18


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Fig. 17.9
Sagittal section of the fetal head at 13 weeks, which shows a prominent forehead (arrows). Increased nuchal translucency can also be noted in this case of trisomy 18 (arrow)


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Fig. 17.10
Transverse section of the fetal head from the same case as in Fig. 17.9, which shows holoprosencephaly, demonstrated by the presence of a single ventricle (arrows)


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Fig. 17.11
Transverse section of the fetal head in a case of trisomy 18 with the presence of holoprosencephaly, characterized by the fusion of the thalami (arrows) and a single ventricle (V)


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Fig. 17.12
Transverse section of the fetal head, which shows an enlargement of the posterior fossa (FP) and agenesis of the cerebellar vermis (white arrow), separating completely the cerebellar hemispheres (HC). These findings are characteristic of Dandy–Walker malformation, which is an indication of karyotype due to the frequent association with trisomy 18 and less frequently with trisomy 13


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Fig. 17.13
Another case of trisomy 18 showing an enlargement of the posterior fossa (calipers)


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Fig. 17.14
Even though it is not a typical finding, encephalocele can be present in cases of trisomy 18 (arrows)


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Fig. 17.15
Transverse section of the fetal thorax showing the four-chamber view and a large ventricular septal defect (arrow) in a case of trisomy 18


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Fig. 17.16
Transverse section of the fetal thorax showing the four-chamber view and a 4-mm ventricular septal defect (arrow and calipers) in a trisomy 18 case. VD = right ventricle, VE = left ventricle


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Fig. 17.17
Large ventricular septal defect (arrow) in a case of trisomy 18


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Fig. 17.18
Section of an unbalanced four-chamber view in a case of trisomy 18 with a complex heart defect


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Fig. 17.19
Left paramedian sagittal section showing an interrupted diaphragm (arrows) and the presence of the stomach (EST) inside the fetal thorax next to the heart (COR), characterizing a left diaphragmatic hernia in a case of trisomy 18


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Fig. 17.20
Transverse section of the fetal thorax showing intrathoracic stomach (ESR) next to the heart (COR), characterizing a diaphragmatic hernia in a case of trisomy 18


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Fig. 17.21
Longitudinal section of a fetus at 13 weeks showing an omphalocele (ONFAL and arrows). The karyotype obtained with chorionic villous sampling showed a trisomy 18 result. MMII = lower limbs, COL = spine, COC = fetal coccyx


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Fig. 17.22
Transverse section of the fetal abdomen showing a small omphalocele (arrows) in a case of trisomy 18. Note the presence of polyhydramnios (P)


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Fig. 17.23
Oblique transverse section of the fetal abdomen showing a small omphalocele (arrows) in a case of trisomy 18. C = spine, VV = umbilical vein, F = intra-abdominal fetal liver


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Fig. 17.24
Transverse section of the fetal abdomen showing a bulky omphalocele (arrows) in a case of trisomy 18. A = fetal abdomen, O = omphalocele


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Fig. 17.25
Longitudinal section of a fetus showing a bulky omphalocele (arrows) in a case of trisomy 18. J = fetal knee and C = fetal head


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Fig. 17.26
Coronal section of a fetus showing hyperechogenic (dysplastic) and enlarged kidneys (arrows) in a case of trisomy 18. B = fetal bladder


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Fig. 17.27
Transverse section of the fetal abdomen on the level of the right kidney (arrows) which is hyperechogenic with a dysplastic aspect and located at a lower position in a case of trisomy 18


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Fig. 17.28
Transverse section (on the left) of the fetal lower back (lumbar spine) showing open spina bifida with a myelomeningocele (arrow) and a median longitudinal section of the fetal spine (on the right) showing a myelomeningocele sac (arrows) in a case of trisomy 18. Isolated neural tube defects are not markers of aneuploidies


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Fig. 17.29
Longitudinal section of the fetal upper limb showing abnormal hands. Malpositioning of limbs is found in cases of trisomy 18. P = wrists, M = hands


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Fig. 17.30
Longitudinal section of the fetal lower limb showing a malpositioned foot (arrow) in a case of trisomy 18. F = fibula


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Fig. 17.31
Evidence for malpositioned hands in the midst of polyhydramnios. M = hand, R = radius, H = polyhydramnios


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Fig. 17.32
Malpositioned foot (arrows) in the midst of polyhydramnios (H)


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Fig. 17.33
Longitudinal section of the fetal hand showing ultrasound appearance of clenched hands. Clichê McAubry. 2 = index finger, 5 = little finger, 3 = middle finger, 4 = ring finger


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Fig. 17.34
Post mortem photograph showing the typical clenched hand observed in Trisomy 18, Edward’s Syndrome. Little finger overlaps ring finger as well index overlaps middle finger. Thumb abduction is also present


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Fig. 17.35
Sequence of images of the same case of trisomy 18. Upper left picture: presence of Dandy Walker malformation (arrow). Lower left picture: presence of dilated cerebral ventricles (arrows). Upper and lower right pictures, presence of heart defect with dilated right chambers (arrows)

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Dec 28, 2017 | Posted by in GYNECOLOGY | Comments Off on Fetal Aneuploidies
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