Acardiac amorphous twin with prune belly sequence in the co-twin

We describe a twin with acardia acephalus or "Twin Reversed Arterial Perfusion Sequence" and prune belly sequence in the co-twin. In a former quite similar case a prune belly appearance of the co-twin of an acardiac fetus was found to be secondary to the ascites caused by cardiac failure. In the present case, we are dealing with the prune belly sequence as a separate condition, given the fact there were no signs of ascites or cardiac failure. We also found associated anomalies: agenesis of the left ureter and kidney, dysplastic right kidney and anal atresia. Urinary tract obstruction has never been described in the co-twin of an acardiac amorphous fetus.