Thoracopagus

THORACOPAGUS, sternopagus, synthorax, a developmental defect in twins consisting of their bodies being joined in the region of the sternum. In some cases, this connection extends along the entire length of the sternum (sternopagus), while in others it is limited to the xiphoid process (xiphopagus). The extension of the fusion in the cranial or caudal direction results in adjacent types of defects (prosopothoracopagus, cephalothoracopagus, face-to-face fusion, head-to-head fusion—see Janus; parasiticus; omphalopagus—fusion at the umbilical regions). Thoracopagi sometimes have a common heart, sometimes a common pericardium, as well as a liver, descending duodenum, and sometimes the common bile duct. In xiphopagi, the organs of the thoracic cavity and intestines are usually properly divided. T. is the most frequent type of conjoined twins. They may be born alive and subsequently remain viable, as demonstrated by the case of the Siamese twins who lived to 63 years of age while joined and each had nine children. When the bridge connecting the twins is minimal, surgical intervention, i.e., separation of the fetuses, may be possible. Often, however, one or both of them die in the process. Cases where, due to underdevelopment of the second twin, only certain parts of the second twin, sometimes formless, are attached to the chest of the first, well-developed twin, are designated as T. parasiticus.