Sonographic features of anal atresia at 12 weeks.

Anorectal atresia results from abnormal development of the anorectal septum. Prenatal diagnosis is difficult but the condition may be suspected by the sonographic demonstration of a dilated colon. We present the sonographic features of a fetus with anal atresia and a ventricular septal defect at 12 weeks of gestation. This case illustrates that a dilated colon may be present in association with fetal anal atresia as early as 12 weeks.