Vascular Disease of the Liver

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Blood is supplied to the liver via both arterial (hepatic artery) and portal venous circulations.
It leaves the liver after passing through the sinusoids by the central and hepatic veins that
enter the inferior vena cava. As each vascular component of the liver may be affected by disease,
there are several distinct clinical and pathological syndromes.

Right-sided heart failure causes passive venous congestion of the liver
Right-sided cardiac failure causes back-pressure in the systemic venous system, which is transmitted
back down the hepatic vein to the central veins, causing mild increase in hepatic size. This
is particularly seen in tricuspid valve incompetence, when the liver is pulsatile. The macroscopic
appearance is described as nutmeg liver, properly called chronic passive venous congestion.
The centrilobular sinusoids are dilated by blood, and the centrilobular hepatocytes are atrophic.
If arterial hypo-tension complicates the right-sided cardiac failure, necrosis of the centrilobular
hepatocytes may occur, with elevation of serum transaminase levels.

Chronic passive venous congestion of the liver causes dark areas where centrilobular zones
are congested by blood, contrasting with pale periportal areas. This appearance is similar to
that of the cut surface of a nutmeg, hence the term 'nutmeg liver'.
The most common causes of portal hypertension are diseases of the liver
Post-sinusoidal portal hypertension is caused by disease of hepatic veins...

PORTAL HYPERTENSION

Portal hypertension is caused by obstruction of blood flow in the portal system
Portal hypertension is a continued elevation in portal venous pressure. This causes back-pressure
in the portal vascular bed, leading to splenomegaly and ascites. New channels open up between the portal
system and systemic venous system, taking the form of varicose venous channels. The main sites
are the lower oesophagus, where oesophageal varices arise and may cause bleeding,
the umbilicus, where the channels are called 'caput medusae'; and the anus, where they
are known as haemorrhoids.
The causes of portal hypertension are best considered on an anatomical basis, according
to the site of obstruction to flow.
Pre-sinusoidal: blockage of vessels before the hepaticsinusoids.
Sinusoidal: blockage in the sinusoids.
Post-sinusoidal: blockage in the central veins, hepatic veins or vena cava.

The three main groups of causes for portal hypertension are:
Presinusoidal
Sinusoidal
Post sinusoidal

Presinusoidal portal hypertension is most often caused by portal vein thrombosis.
Occlusion of the portal venous system at a point before the portal tracts is usually
due to portal vein thrombosis. Predisposing factors are local sepsis, polycythaemia,
and pre-existing sinusoidal portal hypertension due to cirrhosis.
Occlusion of intrahepatic branches causes areas of venous infarction, which are seen
as congested zones with a wedge-shaped pattern.
Such areas are also termed red infarcts or Zahn infarcts.
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