Pylephlebitis (also called pyelophlebitis and infective suppurative thrombosis of the portal vein) is an uncommon thrombophlebitis of the portal vein or any of its branches (i.e. a portal vein thrombosis) that is caused by infection. It is usually a complication of intraabdominal sepsis, most often following diverticulitis, perforated appendicitis, or peritonitis. Considered uniformly lethal in the pre-antibiotic era, it still carries a mortality of 10-30%.

It typically presents with fever, rigors, and right upper quadrant abdominal pain, but sometimes abdominal pain may be absent. Liver function test abnormalities are usually present but frank jaundice is uncommon. In the modern era, it is usually diagnosed by CT scans of the abdomen and pelvis. Bacteriology is often polymicrobial and blood cultures are positive in some cases. A significant fraction of people presenting with this condition have an underlying hypercoagulable state.

Treatment is with a prolonged course of broad-spectrum antibiotics, with the addition of anticoagulants if other clots are present outside the portal vein or if fever persists on antibiotic therapy.

It is a cause of portal hypertension and can cause bowel ischemia sometimes leading to bowel infarction.

Portal vein thrombosis can cause fever, symptoms of indigestion, and gradually worsening abdominal pain. However, it can also develop without causing symptoms, leading to portal hypertension before it is diagnosed. Other symptoms can develop based on the cause. For example, if portal vein thrombosis develops due to liver cirrhosis, bleeding or other signs of liver disease may be present. If portal vein thrombosis develops due to pylephlebitis, signs of infection such as fever, chills, night sweats may be present.

Causes can include pancreatitis, cirrhosis, diverticulitis, and cholangiocarcinoma. It is also a known complication of splenectomy.