Select the appropriate diagnosis or diagnostic indicator for the sonographic image shown below.
The transverse cut through the bladder shows megacystis (ie, the bladder is markedly enlarged) and the distal portion of the urethra can be visualized up to the point of urinary blockage. The blocked urethra acts as a dam that causes the bladder to fill up, then the ureters, and finally the kidneys (hydronephrosis). There is oligohydramnios noted in this picture because by 16 weeks—the gestational age at which this picture was taken— the vast majority of amniotic fluid comes from fetal urine. These pregnancies are usually associated with fetal death due to pulmonary hypoplasia, because the early oligohydramnios does not allow for proper lung development.
The sonographic was performed at approximately 8 weeks after the last menstrual period and shows a placenta but no fetal pole—the classic blighted ovum. Traditionally, 50% of first-trimester spontaneous abortions are said to be chromosomally abnormal. However, more recent evidence suggests that, particularly with advancing age of the mother (ie, in women who are likely to have early ultrasonography for potential CVS), the risk of fetal chromosomal abnormalities is in fact much higher, in many cases approaching even 90% of first-trimester spontaneous abortions.
The cross-section through the fetal head shows a classic lemon sign; that is, there is a frontal bossing of the forehead such that the sides of the forehead are actually pulled in. This is because of the pull on the cisterna magna from spina bifida that is distorting the intracranial contents. This so-called lemon sign has a very high degree of sensitivity, although it is not perfect. The lemon sign disappears in the third trimester and is therefore not useful late in pregnancy.
The longitudinal sonographic image shows the double bubble sign indicating duodenal atresia. The two bubbles are the stomach and the jejunum. This finding is classic for trisomy 21. Approximately onethird of fetuses who have this finding will be found to have trisomy 21, and in this situation, prenatal diagnosis should be offered to document the chromosomes regardless of any other indication the patient may have.
The ultrasound demonstrates dilation of the lateral ventricles consistent with hydrocephalous.