Prenatal diagnosis of cloacal dysgenesis sequence: differential diagnosis from other forms of fetal obstructive uropathy.

Cloacal dysgenesis sequence (CDS) is a rare cause of fetal obstructive uropathy (FOU). The prenatal differentiation of CDS from other FOU is important because CDS is not amenable to in utero surgical intervention in the form of vesicoamniotic shunts. We evaluated the prenatal characteristics of 8 fetuses with CDS, including a pair of monozygotic twins concordant for CDS, in order to identify features that would enable differentiation from other forms of FOU. Pathologic examination in each of the 8 fetuses confirmed characteristic features of absent anal, genital, and urinary orifices associated with a smooth perineum and abnormal phallic development. Associated abnormalities included dysplastic kidneys in 6, hydroureters in 5, intraluminal colonic calcifications in 2, and hypoplastic lungs in 5. Five of these fetuses initially presented as posterior urethral valve syndrome. Six fetuses had megacystis, and 4 underwent vesicocenteses to evaluate urinary electrolytes, all of which were in the 'poor-risk' category. Six fetuses were male and 2 female, contradicting earlier claims that CDS occurs only in females. Evaluation of candidates for in utero surgical intervention should include fetal karyotype, and CDS should be suspected in cases of FOU in whom the karyotype reveals a male fetus and sonographic evaluation demonstrates colonic calcifications or abnormal phallic development. Diagnostic microendoscopy may be of benefit in such cases.