Thoracopagus

Thoracopagus is a form of conjoined twins in which the pair are fused at the chest (thorax) and often share portions of the upper abdomen. It is among the more common varieties of conjoined twinning. The twins are typically connected anteriorly at the sternum and upper abdominal wall and may share one or more thoracoabdominal organs, most notably the heart and pericardium; the liver, upper gastrointestinal tract, and even portions of the vascular system may also be involved. The extent of fusion and organ sharing determines the feasibility of surgical separation and the likelihood of survival.

Embryology and anatomy: Thoracopagus results from incomplete splitting of a single embryo in early development, usually around day 4 to 5 after fertilization. The fused tissues then differentiate into two individuals sharing common structures. The specific anatomy can vary widely; some twins have two hearts with shared vessels, while others have a single heart or extensive cardiac fusion, which significantly influences treatment options and outcomes.

Diagnosis and prognosis: Prenatal ultrasound and fetal magnetic resonance imaging delineate the anatomy and inform prognosis. If there are two separate hearts or limited cardiac sharing, separation may be technically possible in specialized centers. When hearts are fused or there are extensive shared cardiovascular connections, separation is often not viable and mortality is high. Postnatal outcomes depend on the degree of organ sharing and the success of any surgical reconstruction.

Management: Care involves a multidisciplinary team including obstetrics, neonatology, pediatric surgery, cardiology, and radiology. Delivery and postnatal planning occur in specialized centers. In cases where separation is pursued, substantial risks remain, and long-term survival varies with anatomy; many thoracopagus twins face significant medical challenges or may not survive infancy.