ABSTRACT
A case of combined pentalogy of Cantrell with sirenomelia in a monozygotictwin is
described. Similar cases from the world literature are reviewed. Current concepts
on the etiology of anterior midline ventral wall defects and sirenomelia are detailed.
It has been proposed that anterior midline ventral wall defects may be caused by either
monozygotic twinning or vascular dysplasia. Likewise, a vascular steal phenomenon
causes sirenomelia. A common etiology for these defects, an alteration in vascular
development, is proposed.
