Vascular diseases of the liver can result from various conditions involving the hepatic vascular system of the hepatic artery,
portal vein or hepatic veins.
Diagnostic imaging plays an important role for the correct diagnosis in the majority of such cases.
The imaging features of these conditions reflect not only their particular etiology,
but also the specific hepatic parenchymal changes depending on the grade,
level and duration of the hemodynamic changes associated with the different vascular alteration.
We can distinguish hepatic inflow from hepatic outflow diseases.
The hepatic inflow is constituted of the hepatic artery and portal vein located in the center of each hepatic segment,
while the outflow consists of the hepatic veins draining in the inferior vena cava.
The portal vein supplies the 75% of the blood flow to the liver and provides deoxygenated blood that has been drained from the spleen,
pancreas and gastrointestinal tract.
The proper hepatic artery,
a branch of the celiac artery,
supplies the 25% of the blood into the liver and provides oxygenated blood in the liver [1].
In the event of a sudden,
marked reduction in portal vein blood flow,
the arterial blood flow is able to acutely increase,
probably through peribiliary vascular plexus,
to prevent anoxic tissue necrosis.
The hepatic sinusoid and its adjacent microvasculature are sites of complex anastomosis between the high pressure,
low volume hepatic arterial inflow and the low pressure,
high volume portal venous input.
Resistance to flow from portal venous to hepatic venous vessels through hepatic sinusoids is remarkably low [2].
While the blood supply to liver has a dual origin,
all blood leaves the liver through a single venous system: the central veins receive sinusoidal blood and then they unite to form the major hepatic veins.
In the sinusoids,
the blood is processed by hepatocytes,
which can absorb or release nutrients and metabolize toxic chemicals [3].
Deoxygenated blood flow moves out from the lobules through the central veins (located at its center) into the hepatic veins and finally in the vena cava and right atrium.
The study of the functional anatomy of the liver allows the description of a hepatic segmentation based upon the distribution of the portal pedicles and the location of the hepatic veins.
Middle hepatic vein represents the Cantlie line and divides the right from the left liver; right hepatic vein divides right anterior sector and posterior sector.
Utilizing the left hepatic vein,
we identify left lateral and left medial sections. The plane of the portal vein (right and left branches) allows us to divide these different portions of liver into lower segments and upper segments.
We can represent the hepatic vein system as vertical lines and the portal vein as a horizontal one.
We can superimpose on these vessels the eight segments that are described by Couinaud [3].
Third inflow is a normal variant involving an additional venous inflow to the liver,
separate from the usual dual blood supply [2]: this system is composed of aberrant veins that directly enter into the liver independently of the portal venous system.
Pancreaticoduodenal veins can drain into the posterior part of segment IV and usually deliver a higher amount of insulin in comparison to the portal vein.
Therefore,
since insulin promotes the synthesis and deposition of fat in the hepatocytes,
direct drainage of these veins into the liver can cause focal fatty infiltration [4].
The inferior vein of Sappey drains the anterior abdominal wall vessels.
Uncommonly,
pseudolesions can consist of focal steatosis.
A possible explanation is that aberrant drainage of the inferior vein of Sappey may alter local hepatic metabolism and cause fatty infiltration adjacent to the falciform ligament [4].
On the contrary,
gastric and cystic veins contain low concentration of insulin and produce fatty sparing areas,
which are typically located in the posterior part of segments II and IV and adjacent to the gallbladder fossa.
Multiphase helical Computed Tomography (CT) allows the evaluation of the liver during both the later hepatic arterial and the portal venous phases after the injection on contrast agent and therefore has become an important modality for the detection and characterization of perfusion abnormalities.
The dual blood supply system may cause changes in both the volume and the direction of blood flow when a vascular disease occurs [1].
The increasing use of contrast-enhanced,
multiphase helical CT has resulted in more frequent description of the various pathologic conditions involving the hepatic blood vessels.
Radiologists with the knowledge of the pathophysiologic processes that are represented on CT images are often in a position to suggest a specific explanation for the observed hepatic abnormality.
Correlation of imaging features with the clinical report is often essential for an accurate diagnosis,
because some lesion enhancing pattern may mimic mass lesions.
Liver biopsy does not usually contribute to a diagnostically useful information and may be contraindicated in some of these conditions.
In this educational exhibit,
we describe the most common imaging findings of vascular diseases in inflow vessels (portal vein and hepatic artery) and in outflow vessels (hepatic veins) and provide clinical and pathophysiological correlation of the radiological features.