Clínica de Diagnóstico por Imagem (CDPI) & Instituto Fernandes Figueira (IFF) – FIOCRUZRio 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:

Craniofacial

• “Strawberry” calvarium
• Low-set, abnormally shaped ears
• Micrognathia
• Cleft lip or palate
• Thickened nuchal fold or translucency

Central Nervous System

• Choroid plexus cysts
• Myelomeningocele
• Enlarged cisterna magna
• Cerebellar hypoplasia
• Absence of the corpus callosum
• Microcephaly
• Dolichocephaly

Cardiovascular System

• Atrial septal defect
• Membranous ventricular septal defect
• Double-outlet right ventricle
• Atrioventricular canal defect
• Coarctation of the aorta
• Dextroposition of the heart
• Calcification of the chordae tendinea
• Two vessel umbilical cord
• Pulsatile flow in umbilical vein
• Abnormal blood flow during contraction

Gastrointestinal System

• Omphalocele
• Diaphragmatic hernia
• Esophageal atresia / tracheoesophageal fistula
• Anorectal atresia

Urogenital System

• Horseshoe kidneys
• Cystic renal dysplasia
• Hydronephrosis
• Unilateral renal agenesis
• Ambiguous genitalia

Skeletal System

• Overlapping fingers
• Limb-reduction abnormalities
• Club feet
• Rocker-bottom feet

Amniotic fluid volume

• Polyhydramnios or oligohydramnios
• Intrauterine growth restriction
• Small placenta

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

Case ReportThese 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 9).  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:

• “Strawberry” calvarium
• cerebellar hypoplasia
• ventricular septal defect and overriding aorta
• liver herniation with normal insertion of the umbilical cord in the abdomen
• superior limb reduction
• left club foot
• intrauterine growth restriction

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.

References

• 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.