Clues and pitfalls in prenatal diagnosis of classic cloacal exstrophy using ultrasonography and magnetic resonance imaging: A case with sequential observation from 17 to 30 weeks' gestation and literature review.

We observed a case of classic cloacal exstrophy (CE) from 17 to 30 weeks' gestation. At 17 weeks, an omphalocele and single umbilical artery (SUA) were diagnosed with a normal female karyotype on amniocentesis. A pelvic cystic adjacent to SUA, considered to be the bladder at 17 weeks, became swollen to form double cysts at 25 weeks. A phallus-like structure along the lower abdomen was additionally detected, leading to the diagnosis of CE. Fetal magnetic resonance imaging (MRI) at 30 weeks confirmed that the phallus-like structure was of intestinal origin. The presence of a non-visualizable bladder together with abdominal wall defect or omphalocele and an elephant trunk-like deformity are key findings in the prenatal diagnosis of classic CE. Fetal MRI was useful in confirming ultrasonographic findings and obtaining additional findings for the diagnosis of CE. We have discussed clues and potential pitfalls in diagnosing CE, with a review of the literature.