Portosystemic Shunts made easy!

Congenital portosystemic shunts

Which types of portosystemic shunts (PSS) do we differentiate?

Is there an easy way to memorize the classic types of PSS in the dog?

In the following I will try to explain this complex topic in an understandable fashion.

Normal anatomy of the portal vein

Step 1: Intra- or extrahepatic?

Generally it can be said...

Small breed dogs = extrahepatic

Large breed dogs = intrahepatic

Step 2: Remembering what types of PSS exist and how they are classified.

Below you find a short reminder of the different types and the classification of congenital PSS. The following points have to be considered:

  • Number of shunting vessels
  • Insertion of the shunting vessel
  • Origin of the shunting vessels

Additionally it is helpful to consider which PSSs are common and which are less frequently seen.

Intrahepatic PSS – Classification


  • Single PSS
  • Multiple PSS


Intrahepatic PSS always insert into a hepatic vein and thus essentially into the caudal vena cava.


Origin / Course

Right divisional PSS

  • Origin: right intrahepatic branch of the portal vein
  • Course: Lobus hepatis dexter lateralis and Lobus caudatus

Central divisional PSS

  • Origin: right intrahepatic branch of the portal vein
  • Course: Lobus hepatis dexter medialis and Lobus quadratus

Left divisional PSS

  • Origin: left intraheptic branch = persistent Ductus venosus
  • Course: Lobus hepatis sinister medialis and lateralis



  • Right divisional intrahepatic PSS
  • Left divisional intrahepatic PSS


  • Central divisional intrahepatic PSS
  • Multiple congenital intrahepatic PSS
  • Veno-venous collaterals

Extrahepatic PSS – Classification


Congenital extrahepatic PSS are always single vessels! Multiple extrahepatic PSS are always acquired!




  • Insertion: Caudal vena cava


  • Insertion: Azygos vein


  • Insertion: Hepatic vein or caudal vena cava at the level of the diaphragm 


  • Insertion: Left renal vein  


Splenic vein or left gastric vein (left sided PSS)

  • Can be found in: portocaval, portoazygos, portophrenic PSS (origin in right gastric vein is also possible but uncommon)

Gastroduodenal vein (right sided PSS):

  • Can be found in: porto-caval PSS

Right gastric vein (right sided PSS)

  • Can be found in: porto-phrenic PSS

Cranial mesenteric vein (potentially at the origin of the portal vein)

  • Can be found in: porto-renal PSS



  • Porto-caval PSS with origin in the gastroduodenal or splenic vein
  • Porto-azygos PSS with origin in the splenic vein
  • Porto-phrenic PSS with origin in the splenic vein


  • Porto-renal PSS
  • Any other shunts

Step 3: Mnemonic trick – The thing with the loop

To be able to identify the form of PSS you are dealing with it is helpful to remind yourself of the normal anatomy of the portal vein.


The portal vein is entering the liver slightly to the right side. Looking at its intrahepatic branching, a short right branch is coming off the portal vein immediately after entering the liver. It is supplying the right lateral hepatic lobe and the caudate process of the caudate lobe. (N.B. depending on the anatomy text you are using, the right medial hepatic lobe is also supplied by the right branch) intrahepatic portal branch. The remaining and therefore largest portion of the liver is supplied by the left intrahepatic branch of the portal vein.

Easy way to remember:

  • The right intrahepatic branch is small and short
  • The left intrahepatic branch is long.


Therefore intrahepatic PSS arising from the

  • RIGHT branch make a SHORT LOOP.
  • LEFT branch make a LONG LOOP.


But how do I differentiate a central divisional intrahepatic PSS from a right divisional intrahepatic PSS. First it is helpful to remember that central divisional PSS is rare. Therefore it is more likely to have right divisional intrahepatic PSS. Additionally: The CENTRAL divisional intrahepatic PSS is very short and resembles more a FORAMEN. Compared to the right intrahepatic shunt no loop is present. 


For the extrahepatic porto-caval PSS the following applies:

The reverse as for the intrahepatic PSS is true.

  • The right extrahepatic PSS is long.
  • The left extrahepatic PSS is short.


Porto-azygos PSSs are the only ones in which you can see a vessel coursing dorsally to the spinal column. Additionally the azygos vein is enlarged and becomes easily visible cranial to the PSS.


Porto-phrenic PSS arise caudal to the liver. It runs in a large curve along the left side of the liver (seldom right side) towards the diaphragm. The insertion is immediately caudal to the diaphragm and appears to lie within the hepatic parenchyma.

Test yourself – Pug “Whisky”, 5 months

The video starts caudally and goes cranially. Left on the screen is right in the patient.

Does “Whisky” have a PSS and if “yes” which type?

Image courtesy Tierärztliche Klinik Ahlen.  Dr. Gereon Viefhues
Image courtesy Tierärztliche Klinik Ahlen. Dr. Gereon Viefhues

No responsiblity is taken for the correctness of this information. 

© Antje Hartmann