Omphalopagus
Omphalopagus twins are joined at the front and at the level of the umbilicus.
Commonly involved structures are lower thorax fusion and liver fusion. Pericardium may be common, but the heart is never shared. Stomach and the proximal small intestines are usually separate but the small intestines may join at the level of the Meckel diverticulum. The colon separates distally, and each twin has a rectum. There are four arms and four legs with no pelvic or urinary tract union.
Omphalopagus is difficult to differentiate from thoracopagus on the gross survey, the main difference being the absence of cardiac sharing. Omphalopagus twins are the ones with the best chance of survival post-separation.
Diagnosis can be established as early as the 8th week of gestation by transvaginal ultrasound. The ideal time for evaluation is between 11 and 12 weeks.
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