Portal Vein Thrombosis

Excerpt

Portal vein thrombosis (PVT) is a narrowing or blocking of the portal vein by a blood clot. Thrombosis can develop in the main body of the portal vein or its intrahepatic branches and may even extend to the splenic or superior mesenteric veins. PVT frequently occurs with cirrhosis of the liver but may also occur without an associated liver disease like malignancy, abdominal sepsis, or pancreatitis. The extrahepatic portal venous obstruction terminology should be considered a separate entity that refers to developing portal cavernoma or collaterals around chronic portal vein thrombosis.

The portal venous system, originating from the vitelline venous system, close to the umbilical venous system, from the fourth to the twelfth weeks of gestation, drains blood from the gastrointestinal tract (excluding the lower third of the rectum) and biliopancreatic apparatus, including the spleen, pancreas, and gallbladder, to the liver.

The veins that drain the gastrointestinal organs parallel the major arteries that supply the foregut, midgut, and hindgut, including the celiac, superior mesenteric, and inferior mesenteric arteries, respectively. These veins eventually convene at the portal vein, forming a single venous inflow tract into the liver. The celiac vein drains the foregut structures, including the stomach, through the second part of the duodenum. The superior mesenteric vein drains the third part of the duodenum through the initial two-thirds of the transverse colon. The inferior mesenteric vein drains the remaining one-third of the transverse colon through the rectum. These veins comprehensively drain nutrients and toxins from the digestive intake and ultimately provide approximately 75% of the liver's blood supply, with the remaining blood coming from the hepatic artery—eventually draining into the hepatic veins and systemic circulation.

The portal vein forms the confluence of the splenic and superior mesenteric veins, draining the spleen and small intestine, respectively. Portal vein occlusion with thrombosis formation typically occurs in 2 main groups of patients: patients with cirrhosis and patients with prothrombotic disorders. Acute PVT occurs with abrupt thrombotic portal vein occlusion. Portal vein thrombosis can result in complete or partial occlusion of the vein and consequent clot propagation into the mesenteric and splenic tributaries. Features of chronic PVT, such as collateral circulation (eg, cavernous portal transformation) or portal hypertension, have not developed in acute PVT. If the patient's knowledge of when the clot developed is unknown and the patient does not have features of chronic PVT, the PVT can be referred to as being "recent." Managing recent PVT is the same as managing acute PVT.