Caudal regression versus sirenomelia: sonographic clues

Seven cases with the pathologic/autopsy diagnosis of caudal regression or sirenomelia in which antenatal sonography had been performed were reviewed. The three patients with caudal regression had similar findings on antenatal sonogram, including normal or increased amniotic fluid, mild dilation or normal urinary systems, nonfused extremities, and sacral agenesis. In the four patients with sirenomelia, common sonographic findings included marked oligohydramnios, suspected renal agenesis, and sacral agenesis. A history of maternal diabetes was elicited in all patients with caudal regression and in none of the patients with sirenomelia. Findings confirm recent articles in pediatric pathology suggesting that caudal regression is a separate entity, distinct from sirenomelia.