Definition: Trisomy 18 (1/5000 live births) presents with a great phenotypic variability. Intrauterine growth retardation (IUGR) with normal or increased amniotic fluid volume, craniofacial dysmorphism (strawberry-shaped head, micrognathia, choroid plexus cyst), congenital heart disease, omphalocele, large cisterna magna, and abnormal extremities (clenched hands and rocker-bottom feet) are frequently observed anomalies.

At least 30% of affected fetuses have abnormal extremities (unilateral or bilateral), the most frequent one being clenched hand and radial aplasia.

Synopsis

 systemic anomalies

• intra-uterine growth retardation (IUGR)
• low feat activity
• polyhydramnios
• failure to thrive

 placental anomalies

• small placenta
• single umbilcal artery

 cardiovascular anomalies

• ventricular septal defect
• atrial septal defect
• patent ductus arteriosus

 craniofacial anomalies

• short eyelid fissures
• small mouth
• small jaw
• microcephaly
• epicanthal folds
• low set malformed ears
• ceft lip/palate
• eye abnormalites (10%)

 limb anomalies

• clenched hand: clenched fists with the index finger overlapping the 3rd and 4th fingers
• absence of the distal crease on the 5th finger
• low-arch dermal ridge pattern on the fingertips
• nails underdeveloped
• big toe shortened and bent backward (dorsiflexed)
• underdeveloped or absent thumbs
• bilateral club feet
• rocker-bottom feet
• webbed fingers and toes (syndactyly)
• radial aplasia (5-10%)
• arthrogryposis (joint contractures)

 visceral malformations

• diaphragmatic anomalies
• renal malformations
• pulmonary malformations
  • pulmonary lobar anomalies

 redundant skin folds
 cryptorchidism
 spina bifida (6%)
 scoliosis
 omphalocele
 Cantrell pentalogy (#3232702#)

Epidemiology

Prevalence (Since 1961)7 studies: 1/3400 - 1/11000

 1-5000 liveborn
 1-5000 stillborn
 20 - 30% die in the first month
 90% die by age one

Cytogenetics

 trisomy - 95%
 translocation - 2%
 mosaic - 3%