Inseparable thoraco-omphalopagus twins.

Conjoined twins occur at the rate of 1 in 50 to 200,000 live births, and 75% of these share the thorax (thoracopagus) or the thorax and upper abdomen (thoraco-omphalopagus), resulting in cardiac and hepatic sharing. Antenatal diagnosis can delineate the cardiac anatomy and provide parental counseling on whether separation is possible after birth. In the majority of cases, thoracopagus twins have a complex cardiac anatomy and share a common pericardial sac. Separation and survival depend on the extent to which the cardiac chambers and conduction system are fused. When the twins share the atria, ventricles, or both, death is inevitable even if surgical separation is occasionally attempted.