Parapagus twins are conjoined twins that lie side-by-side with ventrolateral fusion.
This type of conjoined twins usually shares the umbilicus, abdomen, and pelvis. The conjoined pelvis may have a single symphysis pubis and one or two sacra.
The lower gastrointestinal tract (single colon and rectum), liver, pancreas, gallbladder, and genitourinary tracts are also usually shared.
The hearts may be fused with complex anatomy. When two hearts are present, the right-sided 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-sided twin.
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