Trisomy 21 presenting with megacystis in the first trimester: a case report

Objective

Fetal megacystis has been reported to occur in 1/1500 pregnancies and defined by a longitudinal bladder diameter of 7mm or more. If the longitudinal bladder diameter is 7-15 mm there is a risk of about 25% that the fetus will have a chromosomal defect. If the bladder diameter is >15 mm, the risk of chromosomal defects is about 10%. We herein present the sonographic and Doppler findings in a fetus with megacystis and trisomy 21.

Case 

A 31-year-old woman, an agricultural engineer, at her first pregnancy has had chemical exposure for 5 years had an operation of patent ductus arteriousus at one and a half year of age and having a sibling with Down Syndrome was referred to antenatal clinics at 13 weeks of gestation due to increased risk of combined test. Nuchal translucency at a crown-rump length(CRL) of 51mm was reported to be 3.3. mm at 11+4 weeks of gestation. Pregnancy associated plasma protein A(PAPP-A) level was 0.35 MOM and free βhCG level was 1.43 MOM Her combined risk was calculated to be under 1/50 at 11th week. Sonographic examination revealed longutidinal bladder diameter of 16 mm with echogenic and enlarged kidneys, absent nasal bone, abnormal ductus venosusu flow, echogenic cardiac focus and tricuspid regurgitation. Chorion villus sampling was performed and karyotype analysis revealed trisomy 21. Patient and her husband were counselled and pregnancy termination with vaginal misoprostol was performed at 14 weeks.

Results

The fetal urinary tract can be visualized ultrasonically from 11 weeks onwards, allowing recognition of megacystis at 11-14 weeks, which warrants comprehensive risk assessment of possible underlying chromosomal aneuploidy. As the evaluations of the nasal bone, ductus venosus, tricuspid valve function, frontomaxillary facial angle, hyperechogenic bowel, intracardiac echogenic focus, and renal pelvis fullness can become part of the 11- to 13 (+6)-week screening test if the imaging protocols are standardized, these markers and detection of fetal megacystitis prompt us to evaluate fetal karyotyping, by using either invasive techniques or fetal DNA from maternal blood.

Conclusion 

Fetal megacystis with increased NT is a severe condition when diagnosed in early pregnancy for chromosomal abnormality and this finding may be an early sign of Trisomy 21.

Keywords

Megacystitis, Trisomy 21