Trisomy 18

2006-02-20-14 Heron Werner, MD, Pedro Daltro, MD Clínica de Diagnóstico por Imagem (CDPI) & Instituto Fernandes Figueira (IFF) – FIOCRUZ – Rio de Janeiro – Brazil

Trisomy 18 is a chromosomal abnormality due to an extra copy of chromosome 18. The prognosis is extremely poor. It was first described by Edwards in 1960. The incidence is approximately 1:3000 to 1:7000 in live births. A variety of sonographic and MRI abnormalities are seen in fetuses with trisomy 18 including:


Central Nervous System:

Cardiovascular System:

Gastrointestinal System:

Urogenital System:

Skeletal System:

Amniotic fluid volume

The differential diagnosis of trisomy 18 includes Pena-Shokeir I syndrome, pseudo trisomy 18, arthrogryposis multiplex congenita, trisomy 9.

Case Report

These are two cases of trisomy 18. The first one is a 40-year-old patient, G2P0, referred to our service at 18 weeks. The ultrasound showed an association of Arnold-Chiari II and valve of posterior urethra (Figures 1 to 8). An amniocentesis was performed and confirmed the karyotype (47,XY+18). The parents decided to interrupt the pregnancy.

Note the dilatation of the bladder and proximal urethra.
Same view with 3D.
Axial view of the cranium showing the "lemon" sign (left image) and the "banana sign" (right image) at 18 weeks.
Left image: Note the meningocele (red arrow) and the dilatation of the bladder (blue arrow). Right image: Note the dilatation of the bladder (red arrow).

Case 2

This is a 31-year-old, G1P0, with a fetus in the first ultrasound examination with multiple malformations. These are the ultrasound images at 12, 18, 21 and 25 weeks. At 21 weeks, a MRI was performed.

3D view showing the abdominal defect. In the 2D image, note the view at the level of the orbits and the herniated liver (red arrow).
The abdominal defect at 21 weeks.
Doppler showing the herniated liver. Note the normal umbilical cord insertion.
The fetal profile, the liver herniation and the umbilical cord cyst at 25 weeks.
Note the small placenta and the normal cord insertion.
Left image: 3D view of the herniated liver. Right image: Axial T1 view showing the herniated liver with a high intensity of signal.
Left image: Axial T2 view of the cephalic pole showing normal lateral ventricles. Right image: T2-weighted view of the small placenta (blue arrow) and liver herniation (red arrow).
Axial T2 view of the cephalic pole at the level of the orbits. Note the mesencephalon (arrow) and the normal brain parenchyma.
Axial T2 of the liver and the normal bladder.
Coronal T2 of the liver herniation. Note on the right image the small abdomen, normal kidneys (blue arrow) and vermis hypoplasia (red arrow).
Sagittal T2 image of the liver herniation. Note the normal umbilical cord insertion and the polyhydramnios.
Sagittal T2 showing the liver herniation. Note the enlarged cisterna magna.
Coronal T2 showing the small abdomen. The brains development looks normal.
View of the small placenta (arrow).
Ultrasound and sagittal T2 images of the superior limb reduction.

The malformations observed were:

The placenta was very small and the polyhydramnios was observed after the 21th week. The chorionic villi sampling was performed at 12 weeks and confirmed the karyotype (47,XX +18). The patient decided to continue the pregnancy but the fetus died intra utero at 26 weeks. The anatomopathology was not authorized by the parents.


Nicolaides KH, Salvesen DR, Snijders RJM, Gosden CM. Strawberry-shaped skull in fetal trisomy 18. Fetal Diagn Ther 7: 132-137, 1992.

Nyberg DA, Kramer D, Resta RG. Prenatal sonographic findings in trisomy 18: review of 47 cases. J Ultrasound Med 2: 103-113, 1993.

Sepulveda W, Treadwell MC, Fisk NM. Prenatal detection of preaxial upper limb reduction in trisomy 18. Obstet Gynecol 85: 847-850, 1995.

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