omphalopagus

Omphalopagus is a form of conjoined twins in which two individuals are fused at the anterior abdominal wall around the umbilicus. The term derives from Greek omphalos, meaning “navel.” In this configuration, the twins typically have separate heads and upper bodies but share a lower chest and abdomen; the fusion may involve the liver and, less commonly, portions of the gastrointestinal tract. The degree of shared viscera varies; the liver is most commonly involved and may be partially or completely shared between the twins. Hearts are usually separate, and the brains are separate, though some cases have fused abdominal structures that complicate separation. The feasibility of surgical separation depends on the extent of shared organs, particularly whether a viable, well-vascularized liver and intact vascular supply can be divided.

Diagnosis is usually established prenatally by ultrasound, with fetal MRI providing detailed anatomy. Postnatally, CT or MRI helps delineate shared structures and plan management. Treatment is individualized and involves a multidisciplinary team. In selected cases with favorable anatomy (e.g., separate hearts and limited shared hepatic tissue), surgical separation has been performed with survival; in others, major organ sharing or complex vascular connections render separation impractical or unsafe.

Prenatal counseling addresses prognosis and potential outcomes, including the risk of mortality and surgical morbidity. Omphalopagus is one of several recognized forms of conjoined twinning, alongside thoracopagus, pygopagus, and craniopagus, and understanding of anatomy guides management and prognosis.