Portal venous pneumatosis (PVG).
Also known as intrahepatic portal venous gas (hepaticportalvenousgas, HPVG), it refers to the presence of gas in the portal vein and its intrahepatic branches and vessels at all levels of the gastrointestinal geniculate branches, often transient and not an independent disease but usually a sign that accompanies gastrointestinal disease, most commonly in intestinal ischemia and necrosis. The sign can also occur in non-digestive pathologies such as sepsis and abdominal infections, and in about 15% of cases PVG is idiopathic.
The synergistic effect of one or more factors can lead to PVG:
(i) destructive changes in the mucosa of the intestinal wall.
(ii) Increased pressure in the alimentary canal.
(iii) Infection with gas-producing bacteria.
Pathogenesis.
It is generally believed that there are two pathways.
1, increased pressure in the intestinal canal, edema and necrosis of the intestinal mucosa layer, destruction of the mucosal barrier, gas in the intestinal lumen entering the small veins of the intestinal wall through the broken mucosa, and reflux to the portal vein through the mesenteric vessels
2.Infection of gas-producing bacteria in the intestine and abdominal cavity spreads to the intestinal mucosa or small vein, and direct infection of gas-producing bacteria in the vein causes pneumatosis in the portal vein.
Ultrasound performance.
(1) The typical manifestation is small dotted strong echogenicity in the lumen of portal vein moving rapidly towards the liver in the direction of blood flow.
(2) With the increase of gas accumulation, the gas will accumulate in the left lobe of the liver to form striated strong echogenicity, and when the gas quantity further increases, it may lead to uneven liver echogenicity.
(3) Intermittent high-intensity burr-like signals are seen in the portal flow spectrum, due to artifacts from Doppler receiver “overload” during processing of these gas-intense echogenic signals.
Differential diagnosis.
The ultrasound presentation of PVG can be differentiated from bile duct pneumatosis in two ways:
(i) the gas of biliary pneumatosis often accumulates in the hilar region, whereas PVG is distributed in the marginal parts of the liver.
(ii) Gas in the portal vein flows rapidly with blood flow, whereas the location of biliary pneumatosis is relatively fixed.
Sometimes the dotted hyperechoic spots in the portal vein may also be aggregated erythrocytes, which can be identified from three aspects:
(i) the echogenic intensity of aggregated red blood cells is lower than that of gas.
(ii) The strong punctate echogenicity of gas tends to appear in the lumen near the anterior wall of the vein because of the low density of bubbles, while aggregated red blood cells do not have this sign.
③The flowing bubble can appear as a characteristic sharp spike burr-like signal during Doppler detection.