Fetal megacystis: differential diagnosis.

The purpose of our retrospective observational series was to determine whether the sonographic characteristics of fetal megacystic bladders can be used to reliably establish the most likely diagnosis in fetuses with this condition. The sonographic records of pregnant patients referred to our institutions over a 10-year period who were found on initial 2-dimensional sonography to be carrying fetuses with megacystis were examined for evidence of a keyhole sign, bladder thickness, amniotic fluid index, and fetal sex. When available, 3-/4-dimensional sonography, Doppler angiography, tomographic ultrasound imaging, virtual organ computer-aided analysis, and automatic volume calculation were used as part of the detailed fetal anatomic survey. Twenty fetuses with megacystis were identified. Seventeen were male; 2 were female; and 1 had ambiguous genitalia. All male fetuses with megacystis originally had a diagnosis of prune belly syndrome. The diagnosis for 10 male fetuses with a keyhole sign was changed to megacystis secondary to posterior urethral valves. The fetus with ambiguous genitalia had prune belly syndrome. One of the female fetuses had a diagnosis of urethral atresia, and the diagnosis for the other female fetus was megacystis-microcolon-intestinal hypoperistalsis syndrome. In conclusion, in fetuses with megacystic bladders, it is possible to distinguish between cases with prune belly syndrome, posterior urethral valves, urethral atresia, and megacystis-microcolon-intestinal hypoperistalsis syndrome by a detailed anatomic survey using 2- and 3-/4-dimensioinal sonographic techniques.