A Case of Thoraco-Omphalopagus Conjoined Twins: Clinical Imaging and Anatomical Classification.

Conjoined twins are a rare phenomenon estimated to occur in a range between 1 in 49,000 births and 1 in 189,000 births. As a product of monochorionic-monoamniotic pregnancies, they are currently believed to result from late, incomplete fission of the bilaminar embryonic disk at 13-15 days gestation. Conjoined twins are typically classified by the point at which their bodies are joined, with 15 recognized types, five of which account for more than 70% of cases. Fusion of the thorax and upper abdomen (thoraco-omphalopagus) accounts for 28% of all cases. Mortality and morbidity rates remain high irrespective of the point of fusion, with 40-60% of cases being lost to miscarriage and stillbirth, and only about 18% of live births surviving more than 24 hours. Given this prognosis, knowledge of underlying anatomy and clinical imaging is paramount to antenatal diagnosis, assessment of viability, and subsequent management of conjoined twins. A case of thoraco-omphalopagus twins with a single heart and single liver discovered on routine ultrasound at 12 weeks gestation is described.