Congenital anomalies of the portal vascular system which result in blood bypassing the hepatic parenchyma lead to the development of hepatic insufficiency. Most commonly seen in young dogs (mean age at onset of clinical signs in one report was 8.4 months), cases of portosystemic shunts are characterized by a wide variety of clinical and pathologic abnormalities.
Boettcher, Tamara and Rigg, Dale L.
"Congenital Portosystemic Shunts in the Canine: A Case Report and Review of the Syndrome, Its Diagnosis and Treatment,"
Iowa State University Veterinarian: Vol. 45
, Article 1.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol45/iss2/1