Hyrtl's anastomosis, the only connection between the two umbilical arteries. A study in full term placentas from AGA infants with normal umbilical artery blood flow.

Abstract

The aim of this study was to describe the variable anatomy in the anastomosis between the umbilical arteries for better understanding of the physical characteristics of the umbilical flow velocity waveform (FVW). The arterial system of 67 placentas from pregnancies with normal umbilical FVW and resulting in a full-term AGA infant was visualized by angiography. The method allowed study of the anatomy of the anastomosis between the umbilical arteries and calculation of the relative placental area supplied by each umbilical artery. In 60 cases there was one anastomosis between the umbilical arteries, in one case there were two, in four the anastomosis was absent, and another two cases had a single umbilical artery. The anastomosis was represented by a vessel, a fenestration or coalescence of the umbilical arteries. In case the anastomosis diameter was of at least that of the umbilical arteries, they supplied in mean 26% and 74% (+/- 8.2%) of the placental area respectively. When the anastomosis diameter was smaller than that of the umbilical arteries their supply areas were in mean 41% and 59% (+/- 6.0%) respectively. In placentas lacking anastomosis the two umbilical arteries supplied 45% and 55% (+/- 2.6%) respectively, indicating a higher degree of symmetry. By using angiography we were able to demonstrate the variable anatomy of the anastomosis of Hyrtl. We found the occurrence and width of the anastomosis was correlated to the symmetry in size between the supply areas of each umbilical artery.