Fetal anal atresia presenting as transient bowel dilatation at 16 weeks of gestation

Congenital anal atresia is a rare abnormality which in two thirds of the cases is associated with other congenital abnormalities or syndromes. Prenatal diagnosis is usually achieved in cases with coexisting abnormalities. The diagnosis of isolated anal atresia is extremely difficult and can be suspected in the presence of colon dilatation. We present the case of a fetus in which marked dilatation of the colon was diagnosed at 16 weeks of gestation. Four weeks later the sonographic appearance of the bowel was normal and remained normal for the rest of the pregnancy. Anal atresia was diagnosed immediately after birth and corrected surgically. No other abnormalities were present. This case report illustrates that in anal atresia, bowel dilatation may be only transient.