Sonographically detected fetal and placental abnormalities associated with trisomy 16 confined to the placenta. A case report and review of the literature.

Trisomy 16 is the most frequent autosomal anomaly seen in early spontaneous abortions, accounting for 15 per cent of all chromosomally abnormal early spontaneous abortions. This trisomy is thought to be lethal in the non-mosaic state and incompatible with full fetal development. We report a case of placental trisomy 16 mosaicism detected after chorionic villus sampling (CVS). The patient was referred at 18 weeks of gestation on account of moderate intra-uterine growth restriction (IUGR). Detailed sonography showed a thickened and enlarged placenta with multiple 'cysts', polyhydramnios, a single umbilical artery and a small ventricular septal defect (VSD). CVS, amniocentesis (AC) and fetal blood sampling (FBS) were performed. After direct preparation of chorionic villi only 47,XX,+16 cells were seen. However, chromosomal analysis of cultivated amniotic fluid cells and fetal lymphocytes only showed a normal karyotype 46,XX. After direct preparation of a second CVS at 19 + 4 weeks of gestation the karyotype 47,XX+16 was confirmed in the contralateral part of the placenta and near the insertion of the umbilical cord. A normal female karyotype 46,XX was demonstrated by extensive karyotyping of various sites of the placenta, the neonatal skin fibroblasts and lymphocytes postnatally. In accordance with this observation the multiple 'cysts' of the placenta disappeared in the third trimester. We speculate that the sonographic findings of multiple round placental 'cysts' without a hyperreflective border may be caused by the trisomic cell lineages and therefore may be a sonographic marker of trisomy 16.