Congenital liver cyst presenting as congenital diaphragmatic hernia.

A 5-day-old infant was found to have an unusual presentation of a congenital liver cyst. The cyst arose from the left lobe of the liver and herniated into the left thoracic cavity through a congenital defect at the central tendinous portion of the diaphragm. The association between a congenital liver cyst and the location of the diaphragmatic hernia suggests that the abnormality occurred during very early embryonic development when the liver rapidly expands and extends into the septum transversum at the base of the heart. A small amount of liver tissue might well have perforated through the thinnest central portion of the septum transversum and underwent cystic degeneration due to incarceration.