Liver agenesis with omphalocele: a report of two human embryos using serial histological sections.

We identified 2 human embryos, with crown-rump lengths (CRLs) of 22 mm and 23 mm and a gestational age of approximately 7 weeks (O'Rahilly's stage 21-22), with liver agenesis and omphalocele. Serial histological sections were prepared of the entire body of one specimen, whereas sections of the neck, including the upper part of the heart, were missed for the other specimen as a result of tissue damage during the abortion. In addition, isolated omphalocele was assessed in another embryo (CRL  =  25 mm) for comparison with atypical omphalocele in the embryos with liver agenesis. The 2 embryos with liver agenesis were characterized by (1) the absence of the anterior part of the diaphragm; (2) abnormality in the venous pole of the heart; (3) a normal stomach in the left upper abdominal cavity; and (4) normal pancreas development with normal midgut rotation. The most likely cause of liver agenesis, when combined with isolated omphalocele, was a defect in the anterior extension or migration of the septum transversum rather than a mechanical separation of the hepatic diverticulum from the septum transversum.