Dicephalus parapagus conjoined twins
Parapagus twins are conjoined twins that lie side-by-side with ventrolateral fusion. They usually share the umbilicus, abdomen, and pelvis. The conjoined pelvis usually has a single symphysis pubis and one or two sacra. The lower gastrointestinal tract is shared, with a single colon and rectum. The hearts may be fused with complex anatomy. When two hearts are present, the right twin’s heart is usually more severely malformed. Defects of laterality, with absent spleen or situs inversus of the right twin’s organs, often accompany heart abnormalities. If the hearts are not fused, abdominal viscera may be situated normally. There are generally two sets of lungs, which may be underdeveloped or anomalous, especially in the right twin. The liver, pancreas, gallbladder, and genitourinary tracts may be shared.