Anatomy of the vitelline vein remnant in human embryos and fetuses.

Abstract

To demonstrate the entire course of the human vitelline vein (VV) in specimens after degeneration of the yolk sac. Sagittal and horizontal histological sections from 8 embryos and 19 fetuses (gestational age approximately 6-12weeks; crown-rump length 11-61mm) were examined. Two types of VV remnants were observed: a long VV on the right superior side of the mesentery of the jejunum (VV1) and a short VV on the left inferior side of the mesentery (VV2). The VV1, observed in 12 specimens, was 20-30 microns in diameter and ran dorsally between the right liver lobe and the jejunum, subsequently merging with an initial superior mesenteric vein on the pancreatic head immediately below the superior portion of the duodenum. The VV2, observed in four specimens, passed dorsally between loops of the ileum on the left side of the mesentery of the ileum and connected to the mesentery. Many of the VVs did not originate from the umbilical cord but suddenly started in the sack of physiological herniation. At 10-12weeks, after herniation, the VVs originated from the umbilicus and were involved by the expanding greater omentum. The right-sided and left-sided VVs seemed to correspond to right and left VV remnants, respectively, and both took an upstream course outside the mesentery of the jejunum and ileum. The right VV upstream portion was likely to disappear later than the left one, but the timing of degeneration varied greatly among individuals, depending on the topographical relationship between the right liver lobe and the jejunum.