UNUSUAL CONGENITAL PORTOSYSTEMIC COMMUNICATION RESULTING FROM PERSISTENCE OF THE EXTRAHEPATIC UMBILICAL VEIN

An unusual congenital portosystemic shunt was identified in one dog an d two cats with clinical signs and laboratory evidence of hepatic dysf unction. In all the animals, the abnormal vessel arose from the portal system between the left medial and quadrate liver lobes and travelled within the falciform fat, exiting the abdomen through the caudal vent ral left diaphragm. The intrathoracic course of these vessels was not established. The anatomical location of this anomalous vessel may have hindered attempts at ultrasonographic identification since it was not visualised before surgery in any of the animals. In addition, while t he anatomical location of the vessel may facilitate rapid identificati on and surgical attenuation, it could predispose the vessel to trauma during the coeliotomy approach. It is hypothesised that this form of p ortosystemic communication results from failure of a portion of the le ft umbilical vein to degenerate during embryogenesis. This is in contr ast to other forms of congenital extrahepatic portosystemic shunt that are presumed to be developmental errors resulting in an abnormal comm unication between the embryonic vitelline and cardinal venous systems. The prognosis for animals with the vascular anomaly reported here is probably similar to that for animals with other forms of congenital po rtosystemic shunt.